[libvirt] conftest segfault

[Gene Czarcinski]

On 03/15/2013 01:26 PM, Eric Blake wrote:
> On 03/15/2013 10:16 AM, Gene Czarcinski wrote:
>> On 03/15/2013 11:38 AM, Eric Blake wrote:
>>> On 03/15/2013 07:48 AM, Gene Czarcinski wrote:
>>>> One of the libvirt tests (conftest) has been segfaulting for some time
>>>> with no indication of a test failure other than a message in syslog.  I
>>>> verified this by building libvirt-1.0.3-1 with mock.
>>> Generally, this is not an issue.  Autoconf tests INTENTIONALLY try to
>>> probe for broken systems, in order to work around brokenness, so a
>>> segfaulting conftest during ./configure just says that things are
>>> probing as expected.  About the only thing that could be done to avoid a
>>> segfault during ./configure is fixing the underlying broken system that
>>> the probe was detecting in the first place, but that's more likely to be
>>> a glibc or kernel fix, not a libvirt fix.
>>>
>> Isn't it a bit strange that it is broken under v1.0.3-maint but not
>> under v1.0.2-maint?  The underlying system is the same.
> It's not broken.  If instead you mean, "Isn't it strange that a
> configure triggers a conftest segfault under v1.0.3-maint but not under
> v1.0.2-maint?", the answer is no, it's not strange - v1.0.3 has more
> probes entered into than v1.0.2, so the new segfault is probably due to
> one of those added probes.
>
> Knowing WHICH configure.ac probe is segfaulting might be nice, for
> diagnosing why it is faulting and where to send a bug report upstream.
> For example, if the bug is in glibc, then fixing glibc to not segfault
> will fix every program that relies on glibc without probing for the bug
> - but it will have no difference to libvirt which is already prepared to
> work around the glibc bug.
>
> Look through the config.log of your 1.0.3 build to see if it you can
> quickly spot a test that failed with a segfault.  There's a wealth of
> information in that file (maybe as simple as finding the string '$? =
> 139' or a message about a SEGV).  But again, a segfault of conftest
> during configure is NORMAL, and nothing to panic about - it means that
> the package is PROPERLY going to avoid tickling that bug later on when
> the package is compiled.
>
> In fact, just in typing that, I though of at least one glibc CVE bug in
> re_compile_pattern, that still has not been fixed as of the glibc
> currently in Fedora 18.  Furthermore, I know that this bug was reported
> only recently, and that the version of gnulib used in v1.0.2 did not
> check for this bug, while the version in v1.0.3 does (see libvirt commit
> d09949e29 for where I updated to newer gnulib, precisely to work around
> that glibc CVE).  So sure enough, I looked through my config.log and found:
>
> configure:31277: checking for working re_compile_pattern
> configure:31456: gcc -std=gnu99 -o conftest -g   conftest.c  >&5
> configure:31456: $? = 0
> configure:31456: ./conftest
> *** glibc detected *** ./conftest: malloc(): memory corruption:
> 0x0000000000b31fc0 ***
> ./configure: line 3528: 15097 Segmentation fault      (core dumped)
> ./conftest$ac_exeext
> configure:31456: $? = 139
> configure: program exited with status 139
>
> Libvirt is immune to that bug, but the CVE still affects other glibc
> clients that use re_compile_pattern without being aware of the problems,
> so you may want to put some pressure on the right people to fix
> https://bugzilla.redhat.com/show_bug.cgi?id=905877.
>
I did a little testing and the problem begins occurring with this commit:

> commit d09949e29386c38443c82a2231240cc1e3954a5d
> Author: Eric Blake <eblake at redhat.com>
> Date:   Sat Jan 26 13:41:31 2013 -0700
>
>     maint: update to latest gnulib
>
>     CVE-2013-0242 in glibc's regex() can cause a DoS in any daemon
>     that runs a regex search on user input while in a multibyte locale.
>     I'm not sure how hard it would be to trigger such a setup for
>     libvirtd, but rather than risk things, we can avoid the issue:
>     gnulib has worked around the problem, and by updating to the latest
>     gnulib, we can avoid the bug even on platforms where glibc has yet
>     to be patched.
>
>     * .gnulib: Update to latest, for various fixes, including regex.
>     * bootstrap: Resync from upstream.

If do a ./autogen with the previous commit, no problem.  Move along to 
this commit and "bang" ... the segfault message in syslog.

So, it appears the this version of gnulib fixes something important but 
also causes a segfault when ./configure is run with the new gnulib.  
What I do not know is if this segfault has any meaning.

Gene