pack-bitmap: prevent pattern leak on pseudo-merge re-assignment

When "bitmapPseudoMerge.*.pattern" appears more than once for the same
group, `pseudo_merge_config()` frees the old `regex_t *` pointer
but does not call `regfree()` on it first. This leaks whatever internal
state `regcomp()` allocated.

The final cleanup path in `pseudo_merge_group_release()` does call
`regfree()` before `free()`, so only the intermediate replacement is
affected.

Fix this by guarding the replacement with a NULL check and calling
`regfree()` before `free()` when the pointer is non-NULL.

Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: ttaylorr

pseudo-merge.c

@@ -150,7 +150,10 @@ static int pseudo_merge_config(const char *var, const char *value,
 	if (!strcmp(key, "pattern")) {
 		struct strbuf re = STRBUF_INIT;
 
-		free(group->pattern);
+		if (group->pattern) {
+			regfree(group->pattern);
+			free(group->pattern);
+		}
 		if (*value != '^')
 			strbuf_addch(&re, '^');
 		strbuf_addstr(&re, value);

t/t5333-pseudo-merge-bitmaps.sh

@@ -662,4 +662,34 @@ test_expect_success 'sampleRate=0 does not cause division by zero' '
 	)
 '
 
+test_expect_success 'duplicate pseudo-merge pattern does not leak' '
+	git init pseudo-merge-dup-pattern &&
+	test_when_finished "rm -fr pseudo-merge-dup-pattern" &&
+
+	(
+		cd pseudo-merge-dup-pattern &&
+
+		test_commit_bulk 64 &&
+		tag_everything &&
+		git repack -ad &&
+
+		pack=$(ls .git/objects/pack/pack-*.pack) &&
+
+		# Set the same group'\''s pattern twice. The second
+		# assignment should cleanly release the compiled regex
+		# from the first without leaking.
+		git config bitmapPseudoMerge.test.pattern "refs/tags/" &&
+		git config --add bitmapPseudoMerge.test.pattern "refs/tags/" &&
+		git config bitmapPseudoMerge.test.maxMerges 1 &&
+		git config bitmapPseudoMerge.test.threshold now &&
+		git config bitmapPseudoMerge.test.stableThreshold never &&
+
+		git rev-parse HEAD~63 |
+		test-tool bitmap write "$(basename $pack)" &&
+
+		test_pseudo_merges >merges &&
+		test_line_count = 1 merges
+	)
+'
+
 test_done