68 lines
1.9 KiB
Ruby
68 lines
1.9 KiB
Ruby
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#!/usr/bin/ruby
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# This file is part of Metasm, the Ruby assembly manipulation suite
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# Copyright (C) 2008 Yoann GUILLOT
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#
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# Licence is LGPL, see LICENCE in the top-level directory
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#
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# this exemple illustrates the use of the PTrace32 class to hijack a syscall in a running process
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# the next syscall made is patched to run the syscall with the arguments of our choice, then
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# run the original intended syscall
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# Works on linux/x86
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#
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require 'metasm'
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class SyscallHooker < Metasm::PTrace32
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CTX = ['EBX', 'ECX', 'EDX', 'ESI', 'EDI', 'EAX', 'ESP', 'EBP', 'EIP', 'ORIG_EAX']
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def inject(sysnr, *args)
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sysnr = SYSCALLNR[sysnr] || sysnr
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syscall
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puts '[*] waiting syscall'
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Process.waitpid(@pid)
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savedctx = CTX.inject({}) { |ctx, reg| ctx.update reg => peekusr(REGS_I386[reg]) }
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if readmem((savedctx['EIP'] - 2) & 0xffff_ffff, 2) != "\xcd\x80"
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puts 'no int 80h seen, cannot replay orig syscall, aborting'
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elsif args.length > 5
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puts 'too may arguments, unsupported, aborting'
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else
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puts "[*] hooking #{SYSCALLNR.index(savedctx['ORIG_EAX'])}"
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# stack pointer to store buffers to
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esp_ptr = savedctx['ESP']
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args.zip(CTX).map { |arg, reg|
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# set syscall args, put buffers on the stack as needed
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if arg.kind_of? String
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esp_ptr -= arg.length
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esp_ptr &= 0xffff_fff0
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writemem(esp_ptr, arg)
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arg = [esp_ptr].pack('L').unpack('l').first
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end
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pokeusr(REGS_I386[reg], arg)
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}
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# patch syscall number
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pokeusr(REGS_I386['ORIG_EAX'], sysnr)
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# run hooked syscall
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syscall
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Process.waitpid(@pid)
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puts "[*] retval: #{'%X' % peekusr(REGS_I386['EAX'])}"
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# restore eax & eip to run the orig syscall
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savedctx['EIP'] -= 2
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savedctx['EAX'] = savedctx['ORIG_EAX']
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savedctx.each { |reg, val| pokeusr(REGS_I386[reg], val) }
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end
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cont
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end
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end
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if $0 == __FILE__
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SyscallHooker.new(ARGV.shift.to_i).inject('write', 2, "testic\n", 7)
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end
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