diff: fix leak when parsing invalid ignore regex option

When parsing invalid ignore regexes passed via the `-I` option we don't
free already-allocated memory, leading to a memory leak. Fix this.

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

diff.c

@@ -5464,9 +5464,13 @@ static int diff_opt_ignore_regex(const struct option *opt,
 	regex_t *regex;
 
 	BUG_ON_OPT_NEG(unset);
+
 	regex = xmalloc(sizeof(*regex));
-	if (regcomp(regex, arg, REG_EXTENDED | REG_NEWLINE))
+	if (regcomp(regex, arg, REG_EXTENDED | REG_NEWLINE)) {
+		free(regex);
 		return error(_("invalid regex given to -I: '%s'"), arg);
+	}
+
 	ALLOC_GROW(options->ignore_regex, options->ignore_regex_nr + 1,
 		   options->ignore_regex_alloc);
 	options->ignore_regex[options->ignore_regex_nr++] = regex;

t/t4013-diff-various.sh

@@ -8,6 +8,7 @@ test_description='Various diff formatting options'
 GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=master
 export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 
+TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 . "$TEST_DIRECTORY"/lib-diff.sh