This is the mail archive of the
mailing list for the glibc project.
Re: [PATCH] Avoid mapping past end of shared object (BZ #18685)
- From: Siddhesh Poyarekar <siddhesh at redhat dot com>
- To: Florian Weimer <fweimer at redhat dot com>
- Cc: libc-alpha at sourceware dot org, roland at hack dot frob dot com
- Date: Fri, 17 Jul 2015 17:51:43 +0530
- Subject: Re: [PATCH] Avoid mapping past end of shared object (BZ #18685)
- Authentication-results: sourceware.org; auth=none
- References: <1437033625-13561-1-git-send-email-siddhesh at redhat dot com> <55A8928D dot 2090409 at redhat dot com> <20150717061558 dot GD19592 at spoyarek dot pnq dot redhat dot com> <55A8E5D5 dot 606 at redhat dot com>
On Fri, Jul 17, 2015 at 01:24:05PM +0200, Florian Weimer wrote:
> Useful information would be that's a debuginfo file. Showing no output
> or garbage is hardly more helpful than crashing because the user still
> doesn't know what's wrong. They won't even report a bug, so we can't
> help them.
The trouble is, you don't know for sure that it is a debuginfo file.
That's where Carlos talked about the need for a new flag.
> Unfortunately, Fedora coverage for non-i386/x86_64 and proprietary
> legacy applications is quite poor.
The patch has been in rhel-6 for a similar amount of time as well,
i.e. since before I started maintaining the tree.
> In this check,
> + if (__glibc_unlikely (ph->p_offset + ph->p_filesz > st.st_size))
> do p_offset and p_filesz correspond to the program header values in the
> file, or have they already been modified?.
They correspond to the program header values, why do you think they
have been modified?
> Looking at the unmodified program header values (as reported by elfutils
> and the gelf_getphdr function) in a fairly large set of RPMs, I do not
> see production ELF files (as opposed debuginfo files or firmware images)
> where this constraint is violated (for type 1 headers, that is). The
> RPMs are from every minor Red Hat Enterprise Linux release going back to
> version 4 and from recent Fedora releases. It's not a complete set of
> everything shipped by Red Hat or Fedora by a long shot, but it strongly
> suggests that we did not have a recent bug introducing systematic
Yes, ELF files (minus debuginfo) build by our assemblers and linkers
should not have this issue.
> One more question, regarding the new check: Is there already a check
> that the addition does not overflow?
There isn't. I intend to add it but it doesn't seem like there's
agreement on including this patch at all.