[2/2] merge: fix memory leaks in cmd_merge()

Commit Message

Elijah Newren Jan. 20, 2022, 7:47 a.m. UTC

From: Elijah Newren <[e-mail]>

There were two commit_lists created in cmd_merge() that were only
conditionally free()'d.  Add a quick conditional call to
free_commit_list() for each of them at the end of the function.

Testing this commit against t6404 under valgrind shows that this patch
fixes the following two leaks:

    16 bytes in 1 blocks are definitely lost in loss record 16 of 126
       at 0x484086F: malloc (vg_replace_malloc.c:380)
       by 0x69FFEB: do_xmalloc (wrapper.c:41)
       by 0x6A0073: xmalloc (wrapper.c:62)
       by 0x52A72D: commit_list_insert (commit.c:556)
       by 0x47FC93: reduce_parents (merge.c:1114)
       by 0x4801EE: collect_parents (merge.c:1214)
       by 0x480B56: cmd_merge (merge.c:1465)
       by 0x40686E: run_builtin (git.c:464)
       by 0x406C51: handle_builtin (git.c:716)
       by 0x406E96: run_argv (git.c:783)
       by 0x40730A: cmd_main (git.c:914)
       by 0x4E7DFA: main (common-main.c:56)

    8 (16 direct, 32 indirect) bytes in 1 blocks are definitely lost in \
    loss record 61 of 126
       at 0x484086F: malloc (vg_replace_malloc.c:380)
       by 0x69FFEB: do_xmalloc (wrapper.c:41)
       by 0x6A0073: xmalloc (wrapper.c:62)
       by 0x52A72D: commit_list_insert (commit.c:556)
       by 0x52A8F2: commit_list_insert_by_date (commit.c:620)
       by 0x5270AC: get_merge_bases_many_0 (commit-reach.c:413)
       by 0x52716C: repo_get_merge_bases (commit-reach.c:438)
       by 0x480E5A: cmd_merge (merge.c:1520)
       by 0x40686E: run_builtin (git.c:464)
       by 0x406C51: handle_builtin (git.c:716)
       by 0x406E96: run_argv (git.c:783)
       by 0x40730A: cmd_main (git.c:914)

There are still 3 leaks in chdir_notify_register() after this, but
chdir_notify_register() has been brought up on the list before and folks
were not a fan of fixing those, so I'm not touching them.

Signed-off-by: Elijah Newren <[e-mail]>
---
 builtin/merge.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

Comments

Junio C Hamano Jan. 22, 2022, 12:05 a.m. UTC | #1

"Elijah Newren via GitGitGadget" <[e-mail]> writes:

>  done:
> +	if (!automerge_was_ok) {
> +		free_commit_list(common);
> +		free_commit_list(remoteheads);
> +	}

I wondered what happens upon a successful automerge.

We call finish_automerge() and come here, and I do see a call to
free_commit_list(common) in finish_automerge(), but the way
remoteheads is used looked a bit iffy.

In finish_automerge(), we use a temporary variable parents to point
remoteheads at it, and conditionally prepend the current HEAD at the
beginning of the parents list.  This is passed to commit_tree(),
which does pop_commit() to consume all commits on the list.

So after commit_tree() returns, all commit_list instances on
remoteheads list, and possibly the one finish_automerge() prepended
for the current HEAD, are all consumed, and there is no need to
call, and it would be wrong to call, free_commit_list(), at this
point.

So, I agree that this conditional freeing is correct.  It was just
it was a bit hard to see.

Thanks.

Patch

diff --git a/builtin/merge.c b/builtin/merge.c
index 74e53cf20a7..bd8fff9b223 100644
--- a/builtin/merge.c
+++ b/builtin/merge.c
@@ -1273,7 +1273,7 @@  int cmd_merge(int argc, const char **argv, const char *prefix)
 	int best_cnt = -1, merge_was_ok = 0, automerge_was_ok = 0;
 	struct commit_list *common = NULL;
 	const char *best_strategy = NULL, *wt_strategy = NULL;
-	struct commit_list *remoteheads, *p;
+	struct commit_list *remoteheads = NULL, *p;
 	void *branch_to_free;
 	int orig_argc = argc;
 
@@ -1752,6 +1752,10 @@  int cmd_merge(int argc, const char **argv, const char *prefix)
 		ret = suggest_conflicts();
 
 done:
+	if (!automerge_was_ok) {
+		free_commit_list(common);
+		free_commit_list(remoteheads);
+	}
 	strbuf_release(&buf);
 	free(branch_to_free);
 	return ret;