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Code Issues Releases Wiki Activity

PackMachBase<T>::canUnpack() finds overlay_offset for decompression

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modified:   p_mach.cpp
	modified:   p_mach.h
This commit is contained in:
John Reiser 2016-09-20 20:07:42 -07:00
parent 57ba965b93
commit ad6914b938
2 changed files with 75 additions and 1 deletions
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75
src/p_mach.cpp
View File

@ -1827,7 +1827,7 @@ void PackMachBase<T>::unpack(OutputFile *fo)
fi->readx(rawmseg, mhdri.sizeofcmds);
// FIXME forgot space left for LC_CODE_SIGNATURE;
// but PackUnix::canUnpack() sets overlay_offset anyway.
// but canUnpack() sets overlay_offset anyway.
//overlay_offset = sizeof(mhdri) + mhdri.sizeofcmds + sizeof(linfo);
fi->seek(overlay_offset, SEEK_SET);
@ -1934,6 +1934,79 @@ void PackMachBase<T>::unpack(OutputFile *fo)
delete [] mhdr;
}
// The prize is the value of overlay_offset: the offset of compressed data
template <class T>
int PackMachBase<T>::canUnpack()
{
unsigned const lc_seg = lc_segment[sizeof(Addr)>>3];
fi->seek(0, SEEK_SET);
fi->readx(&mhdri, sizeof(mhdri));
if (((unsigned) Mach_header::MH_MAGIC + (sizeof(Addr)>>3)) !=mhdri.magic
|| my_cputype !=mhdri.cputype
|| my_filetype !=mhdri.filetype
)
return false;
rawmseg = (Mach_segment_command *)new char[(unsigned) mhdri.sizeofcmds];
fi->readx(rawmseg, mhdri.sizeofcmds);
unsigned style = 0;
off_t offLINK = 0;
unsigned const ncmds = mhdri.ncmds;
Mach_command const *ptr = (Mach_command const *)rawmseg;
for (unsigned j= 0; j < ncmds;
ptr = (Mach_command const *)(ptr->cmdsize + (char const *)ptr), ++j) {
Mach_segment_command const *const segptr = (Mach_segment_command const *)ptr;
if (lc_seg == ptr->cmd) {
if (!strcmp("__XHDR", segptr->segname)) {
// PackHeader precedes __LINKEDIT (pre-Sierra MacOS 10.12)
style = 391; // UPX 3.91
}
if (!strcmp("UPX_DATA", segptr->segname)) {
// PackHeader follows loader at __LINKEDIT (Sierra MacOS 10.12)
style = 392; // UPX 3.92
}
if (!strcmp("__LINKEDIT", segptr->segname)) {
offLINK = segptr->fileoff;
break;
}
}
}
if (0 == style || 0 == offLINK) {
return false;
}
int const small = 32 + sizeof(overlay_offset);
int bufsize = 4096;
if (391 == style) { // PackHeader precedes __LINKEDIT
fi->seek(offLINK - bufsize, SEEK_SET);
} else
if (392 == style) { // PackHeader follows loader at __LINKEDIT
if (bufsize > (fi->st_size() - offLINK)) {
bufsize = fi->st_size() - offLINK;
}
fi->seek(offLINK, SEEK_SET);
}
MemBuffer buf(bufsize);
fi->readx(buf, bufsize);
int i = bufsize;
while (i > small && 0 == buf[--i]) { }
i -= small;
// allow incompressible extents
if (i < 0 || !getPackHeader(buf + i, bufsize - i, true))
return false;
int l = ph.buf_offset + ph.getPackHeaderSize();
if (l < 0 || l + 4 > bufsize)
throwCantUnpack("file corrupted");
overlay_offset = get_te32(buf + i + l);
if ((off_t)overlay_offset >= file_size)
throwCantUnpack("file corrupted");
return true;
}
template <class T>
bool PackMachBase<T>::canPack()

1
src/p_mach.h
View File

@ -683,6 +683,7 @@ public:
virtual void unpack(OutputFile *fo);
virtual bool canPack();
virtual int canUnpack();
virtual unsigned find_SEGMENT_gap(unsigned const k);
protected: