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Re: Make gelf_getphdr more robust?
- From: Mark Wielaard <mjw at redhat dot com>
- To: elfutils-devel at lists dot fedorahosted dot org
- Date: Thu, 06 Feb 2014 14:20:22 +0100
- Subject: Re: Make gelf_getphdr more robust?
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:
+ /* 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?