Re: git-core: try_to_follow_renames(): git killed by SIGSEGV

[Alexandr Miloslavskiy <alexandr.miloslavskiy@syntevo.com>]

Since I like studying crashes and noone else replied, I decided to have 
a look.

The problem is easy to reproduce with this (replace 1.c with any file):
   git log --follow -L 1,1:1.c -- 1.c

It occurs because `opt->pathspec.items` gets cleaned here:
     clear_pathspec
     queue_diffs
         /* must look at the full tree diff to detect renames */
         clear_pathspec(&opt->pathspec);
         DIFF_QUEUE_CLEAR(&diff_queued_diff);
     process_ranges_ordinary_commit
     process_ranges_arbitrary_commit
     line_log_filter
     prepare_revision_walk
     cmd_log_walk
     cmd_log

And on next iteration it crashes in 'try_to_follow_renames' on this line:
     diff_opts.single_follow = opt->pathspec.items[0].match;

I think that bug comes from commit:
     a2bb801f by SZEDER Gábor, 2019-08-21 13:04:24
     line-log: avoid unnecessary full tree diffs

@szeder could you please look into that?

On 27.02.2020 13:56, Ondrej Pohorelsky wrote:
> Hi,
> 
> there is a SIGSEGV appearing in Fedora[0] with Git 2.24.1
> 
> This bug started to appear after update to Git 2.24.1.
> Bug reporter said that Git crashed on him while running VS Code with
> Git Lens extension[1]
> I have tried to reproduce this bug with my own compiled Git with debug
> flags, but sadly SIGSEGV never appeared.
> 
> To me it seems like there is a problem in commit a2bb801f6a[2] which
> changes move_diff_queue() function. This function calls
> diff_tree_oid() that calls try_to_follow_renames(). In the last two
> functions there are no arguments checks.
> 
> Best regards,
> Ondřej Pohořelský
> 
> [0] https://retrace.fedoraproject.org/faf/problems/bthash/?bth=25aa7d7267ab5de548ffca337115cb68f7b65105
> [1] https://bugzilla.redhat.com/show_bug.cgi?id=1791810
> [2] https://git.kernel.org/pub/scm/git/git.git/commit/?id=a2bb801f6a430f6049e5c9729a8f3bf9097d9b34
>