Subject: [PATCH v2 1/2] merge-ort: fix small memory leak in detect_and_process_renames()

From: "Elijah Newren via GitGitGadget" <[email-masked]>
Date: Sun, 20 Feb 2022 01:29:50 +0000

From: Elijah Newren <[email-masked]>

detect_and_process_renames() detects renames on both sides of history
and then combines these into a single diff_queue_struct.  The combined
diff_queue_struct needs to be able to hold the renames found on either
side, and since it knows the (maximum) size it needs, it pre-emptively
grows the array to the appropriate size:

	ALLOC_GROW(combined.queue,
		   renames->pairs[1].nr + renames->pairs[2].nr,
		   combined.alloc);

It then collects the items from each side:

	collect_renames(opt, &combined, MERGE_SIDE1, ...)
	collect_renames(opt, &combined, MERGE_SIDE2, ...)

Note, though, that collect_renames() sometimes determines that some
pairs are unnecessary and does not include them in the combined array.
When it is done, detect_and_process_renames() frees this memory:

	if (combined.nr) {
                ...
		free(combined.queue);
        }

The problem is that sometimes even when there are pairs, none of them
are necessary.  Instead of checking combined.nr, just remove the
if-check; free() knows to skip NULL pointers.  This change fixes the
following memory leak, as reported by valgrind:

==PID== 192 bytes in 1 blocks are definitely lost in loss record 107 of 134
==PID==    at 0xADDRESS: malloc
==PID==    by 0xADDRESS: realloc
==PID==    by 0xADDRESS: xrealloc (wrapper.c:126)
==PID==    by 0xADDRESS: detect_and_process_renames (merge-ort.c:3134)
==PID==    by 0xADDRESS: merge_ort_nonrecursive_internal (merge-ort.c:4610)
==PID==    by 0xADDRESS: merge_ort_internal (merge-ort.c:4709)
==PID==    by 0xADDRESS: merge_incore_recursive (merge-ort.c:4760)
==PID==    by 0xADDRESS: merge_ort_recursive (merge-ort-wrappers.c:57)
==PID==    by 0xADDRESS: try_merge_strategy (merge.c:753)
==PID==    by 0xADDRESS: cmd_merge (merge.c:1676)
==PID==    by 0xADDRESS: run_builtin (git.c:461)
==PID==    by 0xADDRESS: handle_builtin (git.c:713)
==PID==    by 0xADDRESS: run_argv (git.c:780)
==PID==    by 0xADDRESS: cmd_main (git.c:911)
==PID==    by 0xADDRESS: main (common-main.c:52)

Reported-by: Ævar Arnfjörð Bjarmason <[email-masked]>
Signed-off-by: Elijah Newren <[email-masked]>
---
 merge-ort.c | 15 +++++----------
 1 file changed, 5 insertions(+), 10 deletions(-)

diff --git a/merge-ort.c b/merge-ort.c
index d85b1cd99e9..3d7f9feb6f7 100644
--- a/merge-ort.c
+++ b/merge-ort.c
@@ -3086,12 +3086,11 @@ static int detect_and_process_renames(struct merge_options *opt,
 				      struct tree *side1,
 				      struct tree *side2)
 {
-	struct diff_queue_struct combined;
+	struct diff_queue_struct combined = { 0 };
 	struct rename_info *renames = &opt->priv->renames;
-	int need_dir_renames, s, clean = 1;
+	int need_dir_renames, s, i, clean = 1;
 	unsigned detection_run = 0;
 
-	memset(&combined, 0, sizeof(combined));
 	if (!possible_renames(renames))
 		goto cleanup;
 
@@ -3175,13 +3174,9 @@ simple_cleanup:
 		free(renames->pairs[s].queue);
 		DIFF_QUEUE_CLEAR(&renames->pairs[s]);
 	}
-	if (combined.nr) {
-		int i;
-		for (i = 0; i < combined.nr; i++)
-			pool_diff_free_filepair(&opt->priv->pool,
-						combined.queue[i]);
-		free(combined.queue);
-	}
+	for (i = 0; i < combined.nr; i++)
+		pool_diff_free_filepair(&opt->priv->pool, combined.queue[i]);
+	free(combined.queue);
 
 	return clean;
 }
-- 
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