builtin/pull: fix leaking "ff" option

The `opt_ff` field gets populated either via `OPT_PASSTHRU` via
`config_get_ff()` or when `--rebase` is passed. So we sometimes end up
overriding the value in `opt_ff` with another value, but we do not free
the old value, causing a memory leak.

Adapt the type of the variable to be `char *` and consistently assign
allocated strings to it such that we can easily free it when it is being
overridden.

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

Author: pks-t

builtin/pull.c

@@ -84,7 +84,7 @@ static const char *opt_squash;
 static const char *opt_commit;
 static const char *opt_edit;
 static const char *cleanup_arg;
-static const char *opt_ff;
+static char *opt_ff;
 static const char *opt_verify_signatures;
 static const char *opt_verify;
 static int opt_autostash = -1;
@@ -1024,8 +1024,10 @@ int cmd_pull(int argc, const char **argv, const char *prefix)
 		 * "--rebase" can override a config setting of
 		 * pull.ff=only.
 		 */
-		if (opt_rebase >= 0 && opt_ff && !strcmp(opt_ff, "--ff-only"))
-			opt_ff = "--ff";
+		if (opt_rebase >= 0 && opt_ff && !strcmp(opt_ff, "--ff-only")) {
+			free(opt_ff);
+			opt_ff = xstrdup("--ff");
+		}
 	}
 
 	if (opt_rebase < 0)
@@ -1135,7 +1137,8 @@ int cmd_pull(int argc, const char **argv, const char *prefix)
 
 		if (can_ff) {
 			/* we can fast-forward this without invoking rebase */
-			opt_ff = "--ff-only";
+			free(opt_ff);
+			opt_ff = xstrdup("--ff-only");
 			ret = run_merge();
 		} else {
 			ret = run_rebase(&newbase, &upstream);

t/t7601-merge-pull-config.sh

@@ -4,6 +4,7 @@ test_description='git merge
 
 Testing pull.* configuration parsing and other things.'
 
+TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 
 test_expect_success 'setup' '