Re: history: 'reword HEAD' surfaces a memory leak

[Patrick Steinhardt <ps@pks.im>]

On Thu, Sep 03, 2026 at 05:26:44PM +0200, Kristoffer Haugsbakk wrote:
> I get a sanitizer error when I run a simple reword command:
> 
>     $ make SANITIZE=address install
>     $ GIT_EDITOR=true git history reword \
>         --dry-run 3cb9185f65410273787f74333cc027d2ea5daada
>     update HEAD eeb9d4b5c4041739c0a19b4043924513c8aad2d2 3cb9185f65410273787f74333cc027d2ea5daada
> 
>     =================================================================
>     ==116999==ERROR: LeakSanitizer: detected memory leaks
> 
>     Direct leak of 283 byte(s) in 1 object(s) allocated from:
>         #0 0x712d2f6b4887 in __interceptor_malloc ../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:145
>         #1 0x61970a5757b2 in do_xmalloc /home/kristoffer/programming/git-worktree/git-leakcheck/wrapper.c:55
>         #2 0x61970a575ec0 in do_xmallocz /home/kristoffer/programming/git-worktree/git-leakcheck/wrapper.c:89
>         #3 0x61970a575ec0 in do_xmallocz /home/kristoffer/programming/git-worktree/git-leakcheck/wrapper.c:79
>         #4 0x61970a575ec0 in xmallocz_gently /home/kristoffer/programming/git-worktree/git-leakcheck/wrapper.c:102
>         #5 0x61970a309ca0 in unpack_compressed_entry /home/kristoffer/programming/git-worktree/git-leakcheck/packfile.c:1732
>         #6 0x61970a310bf0 in unpack_entry /home/kristoffer/programming/git-worktree/git-leakcheck/packfile.c:1885
>         #7 0x61970a311fbf in cache_or_unpack_entry /home/kristoffer/programming/git-worktree/git-leakcheck/packfile.c:1528
>         #8 0x61970a311fbf in packed_object_info_with_index_pos /home/kristoffer/programming/git-worktree/git-leakcheck/packfile.c:1610
>         #9 0x61970a313097 in packed_object_info /home/kristoffer/programming/git-worktree/git-leakcheck/packfile.c:1720
>         #10 0x61970a313097 in packfile_store_read_object_info /home/kristoffer/programming/git-worktree/git-leakcheck/packfile.c:2214
>         #11 0x61970a2caae8 in odb_source_files_read_object_info odb/source-files.c:58
>         #12 0x61970a2c69a7 in odb_source_read_object_info odb/source.h:326
>         #13 0x61970a2c69a7 in do_oid_object_info_extended /home/kristoffer/programming/git-worktree/git-leakcheck/odb.c:572
>         #14 0x61970a2c69a7 in odb_read_object_info_extended /home/kristoffer/programming/git-worktree/git-leakcheck/odb.c:710
>         #15 0x61970a2c7cbe in odb_read_object /home/kristoffer/programming/git-worktree/git-leakcheck/odb.c:756
>         #16 0x61970a101d5a in repo_get_commit_buffer /home/kristoffer/programming/git-worktree/git-leakcheck/commit.c:399
>         #17 0x61970a101d5a in repo_get_commit_buffer /home/kristoffer/programming/git-worktree/git-leakcheck/commit.c:391
>         #18 0x61970a346bf6 in repo_logmsg_reencode /home/kristoffer/programming/git-worktree/git-leakcheck/pretty.c:716
>         #19 0x619709ebbe64 in commit_tree_ext builtin/history.c:127
>         #20 0x619709ebd17f in commit_tree_with_edited_message builtin/history.c:183
>         #21 0x619709ebd17f in cmd_history_reword builtin/history.c:717
>         #22 0x619709ec186f in cmd_history builtin/history.c:998
>         #23 0x619709d87ca0 in run_builtin /home/kristoffer/programming/git-worktree/git-leakcheck/git.c:506
>         #24 0x619709d87ca0 in handle_builtin /home/kristoffer/programming/git-worktree/git-leakcheck/git.c:782
>         #25 0x619709d8c9a6 in run_argv /home/kristoffer/programming/git-worktree/git-leakcheck/git.c:865
>         #26 0x619709d8c9a6 in cmd_main /home/kristoffer/programming/git-worktree/git-leakcheck/git.c:986
>         #27 0x619709d83f54 in main /home/kristoffer/programming/git-worktree/git-leakcheck/common-main.c:9
>         #28 0x712d2f229d8f in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
> 
>     SUMMARY: AddressSanitizer: 283 byte(s) leaked in 1 allocation(s).

This feels familiar, even though it doesn't reproduce on my machine. Do
you have "i18n.commitencoding" set? In any case, I think the following
patch should fix it:

diff --git a/builtin/history.c b/builtin/history.c
index 000155ad9c..bca95b9d05 100644
--- a/builtin/history.c
+++ b/builtin/history.c
@@ -158,6 +158,7 @@ static int commit_tree_ext(struct repository *repo,
 	*out = lookup_commit_or_die(&rewritten_commit_oid, "rewritten commit");
 
 out:
+	repo_unuse_commit_buffer(repo, commit_with_message, original_message);
 	free_commit_extra_headers(original_extra_headers);
 	strbuf_release(&commit_message);
 	free(original_author);

I know that we've already been discussing this memory leak on the
mailing list at one point in time, and we've already had a patch similar
to the above. So why wasn't this merged...?

Ah, the discussion was in [1]. Cc'ing Kaartic.

Thanks!

Patrick

[1]: https://lore.kernel.org/git/20260614141600.620272-1-kaartic.sivaraam@gmail.com/