Re: bugreport - SEGFAULT on 'git show-branch --current --reflog=3'

From: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Date: Apr 13, 2022, 13:57 UTC
Message-ID: <220413.864k2xgk51.gmgdl@evledraar.gmail.com>
In-Reply-To: <b6113b91-6613-42b5-ca85-1004099b65c4@p1sec.com>

On Wed, Apr 13 2022, Gregory David wrote:

Show 41 quoted lines

> [[PGP Signed Part:Undecided]]
> Hi, this bugreport is about a SEGFAULT on git binary when running in
> this repository (for example, as it also segfault on other private
> repositories): https://framagit.org/groolot-association/osc_looper.git
>
>
> What did you do before the bug happened? (Steps to reproduce your
> issue) I just wanted to list branches, and so playing with 'git
> show-branch --current --reflog=3' in the repository
> https://framagit.org/groolot-association/osc_looper.git
>
> What did you expect to happen? (Expected behavior)
> Not to segfault
>
> What happened instead? (Actual behavior)
> This command fails with a SEGFAULT on version 2.35.1, 2.20.1 and 2.17.1
> It also SEGFAULT on branch 'next' of github git repository.
>
> What's different between what you expected and what actually happened?
> Segfault
>
> Anything else you want to add:
> Segfaut happened when '--current' AND '--reflog=3' are provided together
>
> Please review the rest of the bug report below.
> You can delete any lines you don't wish to share.
>
>
> [System Info]
> git version:
> git version 2.35.1
> cpu: x86_64
> no commit associated with this build
> sizeof-long: 8
> sizeof-size_t: 8
> shell-path: /bin/sh
> uname: Linux 5.16.0-4-amd64 #1 SMP PREEMPT Debian 5.16.12-1 (2022-03-08)
> x86_64
> compiler info: gnuc: 11.2
> libc info: glibc: 2.33
> $SHELL (typically, interactive shell): /usr/bin/zsh

This appears to fix it, but I didn't have time to further validate it, come up with a test etc:

diff --git a/builtin/show-branch.c b/builtin/show-branch.c
index 330b0553b9d..be3890b2dd6 100644
--- a/builtin/show-branch.c
+++ b/builtin/show-branch.c
@@ -881,10 +881,9 @@ int cmd_show_branch(int ac, const char **av, const char *prefix)
 				       get_color_reset_code(), ref_name[i]);
 			}
 
-			if (!reflog) {
+			if (!reflog || !reflog_msg[i])
 				/* header lines never need name */
 				show_one_commit(rev[i], 1);
-			}
 			else
 				puts(reflog_msg[i]);