commit: fix leaking parents when calling `commit_tree_extended()`

When creating commits via `commit_tree_extended()`, the caller passes in
a string list of parents. This call implicitly transfers ownership of
that list to the function, which is quite surprising to begin with. But
to make matters worse, `commit_tree_extended()` doesn't even bother to
free the list of parents in error cases. The result is a memory leak,
and one that the caller cannot fix by themselves because they do not
know whether parts of the string list have already been released.

Refactor the code such that callers can keep ownership of the list of
parents, which is getting indicated by parameter being a constant
pointer now. Free the lists at the calling site and add a common exit
path to those sites as required.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 5 insertions, 1 deletions

diff --git a/builtin/merge.c b/builtin/merge.c
index daed2d4e1e..50b0c87a95 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -895,7 +895,7 @@ static void prepare_to_commit(struct commit_list *remoteheads)
 static int merge_trivial(struct commit *head, struct commit_list *remoteheads)
 {
 	struct object_id result_tree, result_commit;
-	struct commit_list *parents, **pptr = &parents;
+	struct commit_list *parents = NULL, **pptr = &parents;
 
 	if (repo_refresh_and_write_index(the_repository, REFRESH_QUIET,
 					 SKIP_IF_UNCHANGED, 0, NULL, NULL,
@@ -911,7 +911,9 @@ static int merge_trivial(struct commit *head, struct commit_list *remoteheads)
 			&result_commit, NULL, sign_commit))
 		die(_("failed to write commit object"));
 	finish(head, remoteheads, &result_commit, "In-index merge");
+
 	remove_merge_branch_state(the_repository);
+	free_commit_list(parents);
 	return 0;
 }
 
@@ -937,8 +939,10 @@ static int finish_automerge(struct commit *head,
 		die(_("failed to write commit object"));
 	strbuf_addf(&buf, "Merge made by the '%s' strategy.", wt_strategy);
 	finish(head, remoteheads, &result_commit, buf.buf);
+
 	strbuf_release(&buf);
 	remove_merge_branch_state(the_repository);
+	free_commit_list(parents);
 	return 0;
 }