builtin/gc: fix leaking config values

We're leaking config values in git-gc(1) when those values are tracked
as strings. Introduce a new `gc_config_release()` function that releases
this memory to plug those leaks and release old values before populating
the config fields via `git_config_string()` et al.

Note that there is one small gotcha here with the "--prune" option. Next
to passing a string, this option also accepts the "--no-prune" option
that overrides the default or configured value. We thus need to discern
between the option not having been passed by the user and the negative
variant of it. This is done by using a simple sentinel value that lets
us discern these cases.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: pks-t

builtin/gc.c

@@ -139,9 +139,9 @@ struct gc_config {
 	int gc_auto_threshold;
 	int gc_auto_pack_limit;
 	int detach_auto;
-	const char *gc_log_expire;
-	const char *prune_expire;
-	const char *prune_worktrees_expire;
+	char *gc_log_expire;
+	char *prune_expire;
+	char *prune_worktrees_expire;
 	char *repack_filter;
 	char *repack_filter_to;
 	unsigned long big_pack_threshold;
@@ -157,15 +157,25 @@ struct gc_config {
 	.gc_auto_threshold = 6700, \
 	.gc_auto_pack_limit = 50, \
 	.detach_auto = 1, \
-	.gc_log_expire = "1.day.ago", \
-	.prune_expire = "2.weeks.ago", \
-	.prune_worktrees_expire = "3.months.ago", \
+	.gc_log_expire = xstrdup("1.day.ago"), \
+	.prune_expire = xstrdup("2.weeks.ago"), \
+	.prune_worktrees_expire = xstrdup("3.months.ago"), \
 	.max_delta_cache_size = DEFAULT_DELTA_CACHE_SIZE, \
 }
 
+static void gc_config_release(struct gc_config *cfg)
+{
+	free(cfg->gc_log_expire);
+	free(cfg->prune_expire);
+	free(cfg->prune_worktrees_expire);
+	free(cfg->repack_filter);
+	free(cfg->repack_filter_to);
+}
+
 static void gc_config(struct gc_config *cfg)
 {
 	const char *value;
+	char *owned = NULL;
 
 	if (!git_config_get_value("gc.packrefs", &value)) {
 		if (value && !strcmp(value, "notbare"))
@@ -185,15 +195,34 @@ static void gc_config(struct gc_config *cfg)
 	git_config_get_bool("gc.autodetach", &cfg->detach_auto);
 	git_config_get_bool("gc.cruftpacks", &cfg->cruft_packs);
 	git_config_get_ulong("gc.maxcruftsize", &cfg->max_cruft_size);
-	git_config_get_expiry("gc.pruneexpire", (char **) &cfg->prune_expire);
-	git_config_get_expiry("gc.worktreepruneexpire", (char **) &cfg->prune_worktrees_expire);
-	git_config_get_expiry("gc.logexpiry", (char **) &cfg->gc_log_expire);
+
+	if (!git_config_get_expiry("gc.pruneexpire", &owned)) {
+		free(cfg->prune_expire);
+		cfg->prune_expire = owned;
+	}
+
+	if (!git_config_get_expiry("gc.worktreepruneexpire", &owned)) {
+		free(cfg->prune_worktrees_expire);
+		cfg->prune_worktrees_expire = owned;
+	}
+
+	if (!git_config_get_expiry("gc.logexpiry", &owned)) {
+		free(cfg->gc_log_expire);
+		cfg->gc_log_expire = owned;
+	}
 
 	git_config_get_ulong("gc.bigpackthreshold", &cfg->big_pack_threshold);
 	git_config_get_ulong("pack.deltacachesize", &cfg->max_delta_cache_size);
 
-	git_config_get_string("gc.repackfilter", &cfg->repack_filter);
-	git_config_get_string("gc.repackfilterto", &cfg->repack_filter_to);
+	if (!git_config_get_string("gc.repackfilter", &owned)) {
+		free(cfg->repack_filter);
+		cfg->repack_filter = owned;
+	}
+
+	if (!git_config_get_string("gc.repackfilterto", &owned)) {
+		free(cfg->repack_filter_to);
+		cfg->repack_filter_to = owned;
+	}
 
 	git_config(git_default_config, NULL);
 }
@@ -644,12 +673,15 @@ int cmd_gc(int argc, const char **argv, const char *prefix)
 	struct child_process rerere_cmd = CHILD_PROCESS_INIT;
 	struct maintenance_run_opts opts = {0};
 	struct gc_config cfg = GC_CONFIG_INIT;
+	const char *prune_expire_sentinel = "sentinel";
+	const char *prune_expire_arg = prune_expire_sentinel;
+	int ret;
 
 	struct option builtin_gc_options[] = {
 		OPT__QUIET(&quiet, N_("suppress progress reporting")),
-		{ OPTION_STRING, 0, "prune", &cfg.prune_expire, N_("date"),
+		{ OPTION_STRING, 0, "prune", &prune_expire_arg, N_("date"),
 			N_("prune unreferenced objects"),
-			PARSE_OPT_OPTARG, NULL, (intptr_t)cfg.prune_expire },
+			PARSE_OPT_OPTARG, NULL, (intptr_t)prune_expire_arg },
 		OPT_BOOL(0, "cruft", &cfg.cruft_packs, N_("pack unreferenced objects separately")),
 		OPT_MAGNITUDE(0, "max-cruft-size", &cfg.max_cruft_size,
 			      N_("with --cruft, limit the size of new cruft packs")),
@@ -673,8 +705,8 @@ int cmd_gc(int argc, const char **argv, const char *prefix)
 	strvec_pushl(&prune_worktrees, "worktree", "prune", "--expire", NULL);
 	strvec_pushl(&rerere, "rerere", "gc", NULL);
 
-	/* default expiry time, overwritten in gc_config */
 	gc_config(&cfg);
+
 	if (parse_expiry_date(cfg.gc_log_expire, &gc_log_expire_time))
 		die(_("failed to parse gc.logExpiry value %s"), cfg.gc_log_expire);
 
@@ -686,6 +718,10 @@ int cmd_gc(int argc, const char **argv, const char *prefix)
 	if (argc > 0)
 		usage_with_options(builtin_gc_usage, builtin_gc_options);
 
+	if (prune_expire_arg != prune_expire_sentinel) {
+		free(cfg.prune_expire);
+		cfg.prune_expire = xstrdup_or_null(prune_expire_arg);
+	}
 	if (cfg.prune_expire && parse_expiry_date(cfg.prune_expire, &dummy))
 		die(_("failed to parse prune expiry value %s"), cfg.prune_expire);
 
@@ -703,8 +739,11 @@ int cmd_gc(int argc, const char **argv, const char *prefix)
 		/*
 		 * Auto-gc should be least intrusive as possible.
 		 */
-		if (!need_to_gc(&cfg))
-			return 0;
+		if (!need_to_gc(&cfg)) {
+			ret = 0;
+			goto out;
+		}
+
 		if (!quiet) {
 			if (cfg.detach_auto)
 				fprintf(stderr, _("Auto packing the repository in background for optimum performance.\n"));
@@ -713,17 +752,22 @@ int cmd_gc(int argc, const char **argv, const char *prefix)
 			fprintf(stderr, _("See \"git help gc\" for manual housekeeping.\n"));
 		}
 		if (cfg.detach_auto) {
-			int ret = report_last_gc_error();
-
-			if (ret == 1)
+			ret = report_last_gc_error();
+			if (ret == 1) {
 				/* Last gc --auto failed. Skip this one. */
-				return 0;
-			else if (ret)
+				ret = 0;
+				goto out;
+
+			} else if (ret) {
 				/* an I/O error occurred, already reported */
-				return ret;
+				goto out;
+			}
+
+			if (lock_repo_for_gc(force, &pid)) {
+				ret = 0;
+				goto out;
+			}
 
-			if (lock_repo_for_gc(force, &pid))
-				return 0;
 			gc_before_repack(&opts, &cfg); /* dies on failure */
 			delete_tempfile(&pidfile);
 
@@ -749,8 +793,11 @@ int cmd_gc(int argc, const char **argv, const char *prefix)
 
 	name = lock_repo_for_gc(force, &pid);
 	if (name) {
-		if (opts.auto_flag)
-			return 0; /* be quiet on --auto */
+		if (opts.auto_flag) {
+			ret = 0;
+			goto out; /* be quiet on --auto */
+		}
+
 		die(_("gc is already running on machine '%s' pid %"PRIuMAX" (use --force if not)"),
 		    name, (uintmax_t)pid);
 	}
@@ -826,6 +873,8 @@ int cmd_gc(int argc, const char **argv, const char *prefix)
 	if (!daemonized)
 		unlink(git_path("gc.log"));
 
+out:
+	gc_config_release(&cfg);
 	return 0;
 }
 
@@ -1511,6 +1560,8 @@ static int maintenance_run(int argc, const char **argv, const char *prefix)
 			PARSE_OPT_NONEG, task_option_parse),
 		OPT_END()
 	};
+	int ret;
+
 	memset(&opts, 0, sizeof(opts));
 
 	opts.quiet = !isatty(2);
@@ -1532,7 +1583,10 @@ static int maintenance_run(int argc, const char **argv, const char *prefix)
 	if (argc != 0)
 		usage_with_options(builtin_maintenance_run_usage,
 				   builtin_maintenance_run_options);
-	return maintenance_run_tasks(&opts, &cfg);
+
+	ret = maintenance_run_tasks(&opts, &cfg);
+	gc_config_release(&cfg);
+	return ret;
 }
 
 static char *get_maintpath(void)

t/t5304-prune.sh

@@ -7,6 +7,7 @@ test_description='prune'
 GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME=main
 export GIT_TEST_DEFAULT_INITIAL_BRANCH_NAME
 
+TEST_PASSES_SANITIZE_LEAK=true
 . ./test-lib.sh
 
 day=$((60*60*24))