cgit segfaults

[Robby Workman]

On Wed, 16 Aug 2017 09:36:28 +0100
John Keeping <john at keeping.me.uk> wrote:

> On Wed, Aug 16, 2017 at 01:26:52AM -0500, Robby Workman wrote:
> > We're running cgit-1.1 with git-2.10.4 at
> > https://git.slackbuilds.org and are seeing some reproducible
> > segfaults.
> > 
> > root at git:/var/log# dmesg -T
> > [Wed Aug 16 01:14:23 2017] traps: cgit.cgi[2210] general protection
> > ip:4515bd sp:7ffd787a9470 error:0 in cgit.cgi[400000+103000]
> > 
> > This can be reliably triggered (i.e. every time) with at least one
> > particular link (I'll share it privately with cgit devs, but since
> > I don't know if there's any security impact, I'm not going to put
> > it out on the list as yet).
> > 
> > I've applied 1b4ef6783a71962f8b5da3a23f283 and
> > c699866699411346c5dba4064575 from git master since they appeared to
> > address some segfaults, but apparently they were unrelated to
> > whatever it is that we're seeing. 
> > 
> > Aside from (obviously) sharing the reproducer, any tips on
> > debugging this? We of course have a strong preference for debugging
> > tips that don't impact services on the machine, but if needed,
> > we'll do what we have to do...  
> 
> You can run cgit from the command line with your config and the URL
> using something like:
> 
> 	CGIT_CONFIG=/path/to/cgitrc QUERY_STRING=url=cgit/repo/...
> cgit
> 
> This is what the tests do in tests/setup.sh::cgit_url().
> 
> That should allow you to build a debug binary and reproduce under that
> without a webserver involved, which means you can run under gdb or
> valgrind.


Okay, that's helpful - thanks! I've got something that seems to point
at git's pathspec.c (we're building with (and using on the machine)
git-2.10.4 currently), but I have no idea where to go from here. 
This is the gdb output:

(gdb) run
Starting program: /var/www/cgi-bin/cgit.cgi 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib64/libthread_db.so.1".
Content-Type: text/plain; charset=UTF-8
Content-Disposition: inline; filename="82746b4b48cec68acdbb5b7a5ad841b1a21872af..65131f01e212203fbde61d3074640651a02cb6e0.patch"
Last-Modified: Thu, 24 Aug 2017 06:08:13 GMT
Expires: Thu, 24 Aug 2017 06:13:13 GMT


Program received signal SIGSEGV, Segmentation fault.
0x00000000004515bd in prefix_pathspec (elt=0x6234623634373238 <error: Cannot access memory at address 0x6234623634373238>, prefixlen=0, prefix=0x0, flags=0, 
    raw=0x77a138, p_short_magic=<synthetic pointer>, item=0x77a808) at pathspec.c:149
149		if (elt[0] != ':' || literal_global ||
(gdb) 

-RW
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