[Bug 1931391] [NEW] [SRU] git bisect start crashed with SIGSEGV in buffer_slab_peek()

[Launchpad Bug Tracker]

You have been subscribed to a public bug by Sudip Mukherjee (sudipmuk):

[ Impact ]

"git bisect--helper --bisect-start <paths>" is a valid command to start the git bisect.
And if any user uses the command to bisect then it will result in a segfault and is unusable for the user.

But git bisect--helper is not completely unusable, it can still be used
if the bad commit SHA and good commit SHA is mentioned with the command.

[ Test Plan ]

 * clone any git repo
 * Use the command "git bisect--helper --bisect-start <file>" where <file> is any file in that git repo.

[ Where problems could occur ]

 This is an upstream patch which has been backported. The upstream patch
is fixing the way it treats invalid oid. The upstream patch was applied
in 2020 and considering the number of users using 'git' and considering
that there has been no reported regression for this patch so I will
assume the chances of regression for us is very less.

 The only problem I could find was that one user was confused as there was no message after starting the bisect, and that has been fixed via https://github.com/git/git/commit/0cf1defa5a6764b8a0fd956ff4d114cb014cb8a4. But I feel this patch is an improvement and is not a fix suitable for a stable release.
 
[ Other Info ]

 * The problem has been fixed by upstream in v2.29.0 so as a result only
Focal is affected. Jammy, Lunar, Mantic and Noble are not affected.

[ Original Bug Description ]

`git bisect start <filename>` always exits with a Segmentation fault.

ProblemType: Crash
DistroRelease: Ubuntu 20.04
Package: git 1:2.25.1-1ubuntu3.1
ProcVersionSignature: Ubuntu 5.4.0-65.73-generic 5.4.78
Uname: Linux 5.4.0-65-generic x86_64
ApportVersion: 2.20.11-0ubuntu27.18
Architecture: amd64
CasperMD5CheckResult: skip
CurrentDesktop: XFCE
Date: Wed Jun  9 11:24:04 2021
ExecutablePath: /usr/bin/git
InstallationDate: Installed on 2016-02-27 (1929 days ago)
InstallationMedia: Xubuntu 15.10 "Wily Werewolf" - Release amd64 (20151021)
ProcCmdline: git bisect--helper --bisect-start synapse/storage/persist_events.py
SegvAnalysis:
 Segfault happened at: 0x55d3ab6b0cde <get_cached_commit_buffer+14>:	mov    0x48(%rsi),%esi
 PC (0x55d3ab6b0cde) ok
 source "0x48(%rsi)" (0x00000048) not located in a known VMA region (needed readable region)!
 destination "%esi" ok
SegvReason: reading NULL VMA
Signal: 11
SourcePackage: git
StacktraceTop:
 buffer_slab_peek (c=0x0, s=<optimized out>) at commit.c:290
 get_cached_commit_buffer (r=r at entry=0x55d3ab8e0680 <the_repo>, commit=commit at entry=0x0, sizep=sizep at entry=0x0) at commit.c:290
 repo_get_commit_buffer (r=r at entry=0x55d3ab8e0680 <the_repo>, commit=commit at entry=0x0, sizep=sizep at entry=0x0) at commit.c:306
 repo_logmsg_reencode (r=r at entry=0x55d3ab8e0680 <the_repo>, commit=commit at entry=0x0, commit_encoding=commit_encoding at entry=0x7ffc63d83518, output_encoding=output_encoding at entry=0x55d3ab80257a "UTF-8") at pretty.c:614
 repo_format_commit_message (r=0x55d3ab8e0680 <the_repo>, commit=commit at entry=0x0, format=format at entry=0x55d3ab815233 "%s", sb=sb at entry=0x7ffc63d83610, pretty_ctx=pretty_ctx at entry=0x7ffc63d83630) at pretty.c:1640
Title: git crashed with SIGSEGV in buffer_slab_peek()
UpgradeStatus: Upgraded to focal on 2021-02-16 (112 days ago)
UserGroups: adm cdrom dialout dip docker input libvirt libvirtd lpadmin plugdev sambashare sbuild sudo wireshark
modified.conffile..etc.apport.crashdb.conf: [modified]
mtime.conffile..etc.apport.crashdb.conf: 2021-06-09T11:10:35.636012
separator:

** Affects: git (Ubuntu)
     Importance: Medium
         Status: Fix Released

** Affects: git (Ubuntu Focal)
     Importance: Undecided
         Status: Confirmed


** Tags: amd64 apport-crash focal
-- 
[SRU] git bisect start crashed with SIGSEGV in buffer_slab_peek()
https://bugs.launchpad.net/bugs/1931391
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