On Wed, 2014-02-05 at 18:52 +0100, Florian Weimer wrote:
readelf does this:
GElf_Phdr *phdr = gelf_getphdr (ebl->elf, cnt, &mem);
…
if (phdr->p_type == PT_INTERP)
{
/* We can show the user the name of the interpreter. */
size_t maxsize;
char *filedata = elf_rawfile (ebl->elf, &maxsize);
if (filedata != NULL && phdr->p_offset < maxsize)
printf (gettext ("\t[Requesting program interpreter: %s]\n"),
filedata + phdr->p_offset);
}
The check against maxsize is insufficient, it's also required to check
that phdr->p_filesz <= maxsize - phdr->p_offset. Would it make sense to
do both checks inside gelf_getphdr?
I think this case is actually caught now by default by the integrated
robustify patches from last month, specifically:
https://git.fedorahosted.org/cgit/elfutils.git/commit/?id=720383c53b435de...
+ /* First see whether the information in the ELF header is
+ valid and it does not ask for too much. */
+ if (unlikely (ehdr->e_phoff >= elf->maximum_size)
+ || unlikely (elf->maximum_size - ehdr->e_phoff < size))
+ {
+ /* Something is wrong. */
+ __libelf_seterrno (ELF_E_INVALID_PHDR);
+ goto out;
+ }
So that would make the maxsize check in readelf.c redundant.
And the printf call can leak data or crash if filedata +
phdr->p_offset
is not NUL terminated (which obviously needs a crafted ELF file). This
can't be fixed in gelf_getphdr, alas.
Yes, it would probably be good to catch this in eu-readelf.
Did you catch this by code inspection or did you stumble upon a bad ELF
file that made it crash?
Thanks,
Mark