use-after-free leads to git-blame writing garbage in error message

From: Mike Hommey <mh@glandium.org>
Date: Feb 3, 2015, 09:17 UTC
Message-ID: <20150203091715.GA25445@glandium.org>

Symptoms:
  $ git blame HEAD -- foo
  fatal: no such path foo in <random garbage>

Expected output:
  $ git blame HEAD -- foo
  fatal: no such path foo in HEAD

Bisect says this was introduced in 1da1e07c835e900337714cfad6c32a8dc0b36ac3

valgrind output looks like this: ==4738== Memcheck, a memory error detector ==4738== Copyright (C) 2002-2013, and GNU GPL'd, by Julian Seward et al. ==4738== Using Valgrind-3.10.0 and LibVEX; rerun with -h for copyright info ==4738== Command: ./git-blame HEAD -- foo ==4738== ==4738== Invalid read of size 1 ==4738== at 0x58B6F00: vfprintf (vfprintf.c:1636) ==4738== by 0x58E1298: vsnprintf (vsnprintf.c:119) ==4738== by 0x5107ED: vreportf (usage.c:12) ==4738== by 0x510823: die_builtin (usage.c:36) ==4738== by 0x510A82: die (usage.c:103) ==4738== by 0x41318F: cmd_blame (blame.c:2716) ==4738== by 0x405B52: run_builtin (git.c:351) ==4738== by 0x405B52: handle_builtin (git.c:530) ==4738== by 0x404C69: main (git.c:653) ==4738== Address 0x5f042d0 is 0 bytes inside a block of size 5 free'd ==4738== at 0x4C29E90: free (vg_replace_malloc.c:473) ==4738== by 0x4C1621: object_array_release_entry.isra.0 (object.c:354) ==4738== by 0x4C1F73: object_array_clear (object.c:380) ==4738== by 0x4E8E05: prepare_revision_walk (revision.c:2739) ==4738== by 0x41153E: cmd_blame (blame.c:2705) ==4738== by 0x405B52: run_builtin (git.c:351) ==4738== by 0x405B52: handle_builtin (git.c:530) ==4738== by 0x404C69: main (git.c:653) ==4738== ==4738== Invalid read of size 1 ==4738== at 0x58E50D0: _IO_default_xsputn (genops.c:475) ==4738== by 0x58B6EC1: vfprintf (vfprintf.c:1636) ==4738== by 0x58E1298: vsnprintf (vsnprintf.c:119) ==4738== by 0x5107ED: vreportf (usage.c:12) ==4738== by 0x510823: die_builtin (usage.c:36) ==4738== by 0x510A82: die (usage.c:103) ==4738== by 0x41318F: cmd_blame (blame.c:2716) ==4738== by 0x405B52: run_builtin (git.c:351) ==4738== by 0x405B52: handle_builtin (git.c:530) ==4738== by 0x404C69: main (git.c:653) ==4738== Address 0x5f042d0 is 0 bytes inside a block of size 5 free'd ==4738== at 0x4C29E90: free (vg_replace_malloc.c:473) ==4738== by 0x4C1621: object_array_release_entry.isra.0 (object.c:354) ==4738== by 0x4C1F73: object_array_clear (object.c:380) ==4738== by 0x4E8E05: prepare_revision_walk (revision.c:2739) ==4738== by 0x41153E: cmd_blame (blame.c:2705) ==4738== by 0x405B52: run_builtin (git.c:351) ==4738== by 0x405B52: handle_builtin (git.c:530) ==4738== by 0x404C69: main (git.c:653) ==4738== ==4738== Invalid read of size 1 ==4738== at 0x58E50DE: _IO_default_xsputn (genops.c:474) ==4738== by 0x58B6EC1: vfprintf (vfprintf.c:1636) ==4738== by 0x58E1298: vsnprintf (vsnprintf.c:119) ==4738== by 0x5107ED: vreportf (usage.c:12) ==4738== by 0x510823: die_builtin (usage.c:36) ==4738== by 0x510A82: die (usage.c:103) ==4738== by 0x41318F: cmd_blame (blame.c:2716) ==4738== by 0x405B52: run_builtin (git.c:351) ==4738== by 0x405B52: handle_builtin (git.c:530) ==4738== by 0x404C69: main (git.c:653) ==4738== Address 0x5f042d2 is 2 bytes inside a block of size 5 free'd ==4738== at 0x4C29E90: free (vg_replace_malloc.c:473) ==4738== by 0x4C1621: object_array_release_entry.isra.0 (object.c:354) ==4738== by 0x4C1F73: object_array_clear (object.c:380) ==4738== by 0x4E8E05: prepare_revision_walk (revision.c:2739) ==4738== by 0x41153E: cmd_blame (blame.c:2705) ==4738== by 0x405B52: run_builtin (git.c:351) ==4738== by 0x405B52: handle_builtin (git.c:530) ==4738== by 0x404C69: main (git.c:653) ==4738== fatal: no such path foo in HEAD ==4738== ==4738== HEAP SUMMARY: ==4738== in use at exit: 733,417 bytes in 807 blocks ==4738== total heap usage: 1,505 allocs, 698 frees, 915,428 bytes allocated ==4738== ==4738== LEAK SUMMARY: ==4738== definitely lost: 0 bytes in 0 blocks ==4738== indirectly lost: 0 bytes in 0 blocks ==4738== possibly lost: 0 bytes in 0 blocks ==4738== still reachable: 733,417 bytes in 807 blocks ==4738== suppressed: 0 bytes in 0 blocks ==4738== Rerun with --leak-check=full to see details of leaked memory ==4738== ==4738== For counts of detected and suppressed errors, rerun with: -v ==4738== ERROR SUMMARY: 9 errors from 3 contexts (suppressed: 0 from 0)

Cheers,

Mike