config API: add "string" version of *_value_multi(), fix segfaults

Fix numerous and mostly long-standing segfaults in consumers of
the *_config_*value_multi() API. As discussed in the preceding commit
an empty key in the config syntax yields a "NULL" string, which these
users would give to strcmp() (or similar), resulting in segfaults.

As this change shows, most users users of the *_config_*value_multi()
API didn't really want such an an unsafe and low-level API, let's give
them something with the safety of git_config_get_string() instead.

This fix is similar to what the *_string() functions and others
acquired in[1] and [2]. Namely introducing and using a safer
"*_get_string_multi()" variant of the low-level "_*value_multi()"
function.

This fixes segfaults in code introduced in:

  - d811c8e17c6 (versionsort: support reorder prerelease suffixes, 2015-02-26)
  - c026557a373 (versioncmp: generalize version sort suffix reordering, 2016-12-08)
  - a086f921a72 (submodule: decouple url and submodule interest, 2017-03-17)
  - a6be5e6764a (log: add log.excludeDecoration config option, 2020-04-16)
  - 92156291ca8 (log: add default decoration filter, 2022-08-05)
  - 50a044f1e40 (gc: replace config subprocesses with API calls, 2022-09-27)

There are now two users ofthe low-level API:

- One in "builtin/for-each-repo.c", which we'll convert in a
  subsequent commit.

- The "t/helper/test-config.c" code added in [3].

As seen in the preceding commit we need to give the
"t/helper/test-config.c" caller these "NULL" entries.

We could also alter the underlying git_configset_get_value_multi()
function to be "string safe", but doing so would leave no room for
other variants of "*_get_value_multi()" that coerce to other types.

Such coercion can't be built on the string version, since as we've
established "NULL" is a true value in the boolean context, but if we
coerced it to "" for use in a list of strings it'll be subsequently
coerced to "false" as a boolean.

The callback pattern being used here will make it easy to introduce
e.g. a "multi" variant which coerces its values to "bool", "int",
"path" etc.

1. 40ea4ed9032 (Add config_error_nonbool() helper function,
   2008-02-11)
2. 6c47d0e8f39 (config.c: guard config parser from value=NULL,
   2008-02-11).
3. 4c715ebb96a (test-config: add tests for the config_set API,
   2014-07-28)

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

12 files changed, 105 insertions, 22 deletions

diff --git a/builtin/gc.c b/builtin/gc.c
index 2b3da377d5..9497bdf23e 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -1510,7 +1510,7 @@ static int maintenance_register(int argc, const char **argv, const char *prefix)
 	if (git_config_get("maintenance.strategy"))
 		git_config_set("maintenance.strategy", "incremental");
 
-	if (!git_config_get_value_multi(key, &list)) {
+	if (!git_config_get_string_multi(key, &list)) {
 		for_each_string_list_item(item, list) {
 			if (!strcmp(maintpath, item->string)) {
 				found = 1;
@@ -1578,8 +1578,8 @@ static int maintenance_unregister(int argc, const char **argv, const char *prefi
 		git_configset_add_file(&cs, config_file);
 	}
 	if (!(config_file
-	      ? git_configset_get_value_multi(&cs, key, &list)
-	      : git_config_get_value_multi(key, &list))) {
+	      ? git_configset_get_string_multi(&cs, key, &list)
+	      : git_config_get_string_multi(key, &list))) {
 		for_each_string_list_item(item, list) {
 			if (!strcmp(maintpath, item->string)) {
 				found = 1;
diff --git a/builtin/log.c b/builtin/log.c
index cc9d92f95d..cd17f31171 100644
--- a/builtin/log.c
+++ b/builtin/log.c
@@ -184,8 +184,8 @@ static void set_default_decoration_filter(struct decoration_filter *decoration_f
 	struct string_list *include = decoration_filter->include_ref_pattern;
 	const struct string_list *config_exclude;
 
-	if (!git_config_get_value_multi("log.excludeDecoration",
-					&config_exclude)) {
+	if (!git_config_get_string_multi("log.excludeDecoration",
+					 &config_exclude)) {
 		struct string_list_item *item;
 		for_each_string_list_item(item, config_exclude)
 			string_list_append(decoration_filter->exclude_ref_config_pattern,
diff --git a/config.c b/config.c
index 1f654daf6f..92d9e7e968 100644
--- a/config.c
+++ b/config.c
@@ -2434,6 +2434,25 @@ int git_configset_get_value_multi(struct config_set *cs, const char *key,
 	return 0;
 }
 
+static int check_multi_string(struct string_list_item *item, void *util)
+{
+	return item->string ? 0 : config_error_nonbool(util);
+}
+
+int git_configset_get_string_multi(struct config_set *cs, const char *key,
+				   const struct string_list **dest)
+{
+	int ret;
+
+	if ((ret = git_configset_get_value_multi(cs, key, dest)))
+		return ret;
+	if ((ret = for_each_string_list((struct string_list *)*dest,
+					check_multi_string, (void *)key)))
+		return ret;
+
+	return 0;
+}
+
 int git_configset_get(struct config_set *cs, const char *key)
 {
 	struct config_set_element *e;
@@ -2602,6 +2621,13 @@ int repo_config_get_value_multi(struct repository *repo, const char *key,
 	return git_configset_get_value_multi(repo->config, key, dest);
 }
 
+int repo_config_get_string_multi(struct repository *repo, const char *key,
+				 const struct string_list **dest)
+{
+	git_config_check_init(repo);
+	return git_configset_get_string_multi(repo->config, key, dest);
+}
+
 int repo_config_get_string(struct repository *repo,
 			   const char *key, char **dest)
 {
@@ -2717,6 +2743,12 @@ int git_config_get_value_multi(const char *key, const struct string_list **dest)
 	return repo_config_get_value_multi(the_repository, key, dest);
 }
 
+int git_config_get_string_multi(const char *key,
+				const struct string_list **dest)
+{
+	return repo_config_get_string_multi(the_repository, key, dest);
+}
+
 int git_config_get_string(const char *key, char **dest)
 {
 	return repo_config_get_string(the_repository, key, dest);
diff --git a/config.h b/config.h
index f228fa9d5d..65e569e739 100644
--- a/config.h
+++ b/config.h
@@ -473,6 +473,19 @@ int git_configset_get_value_multi(struct config_set *cs, const char *key,
 				  const struct string_list **dest);
 
 /**
+ * A validation wrapper for git_configset_get_value_multi() which does
+ * for it what git_configset_get_string() does for
+ * git_configset_get_value().
+ *
+ * The configuration syntax allows for "[section] key", which will
+ * give us a NULL entry in the "struct string_list", as opposed to
+ * "[section] key =" which is the empty string. Most users of the API
+ * are not prepared to handle NULL in a "struct string_list".
+ */
+int git_configset_get_string_multi(struct config_set *cs, const char *key,
+				   const struct string_list **dest);
+
+/**
  * Clears `config_set` structure, removes all saved variable-value pairs.
  */
 void git_configset_clear(struct config_set *cs);
@@ -522,6 +535,9 @@ int repo_config_get_value(struct repository *repo,
 RESULT_MUST_BE_USED
 int repo_config_get_value_multi(struct repository *repo, const char *key,
 				const struct string_list **dest);
+RESULT_MUST_BE_USED
+int repo_config_get_string_multi(struct repository *repo, const char *key,
+				 const struct string_list **dest);
 int repo_config_get_string(struct repository *repo,
 			   const char *key, char **dest);
 int repo_config_get_string_tmp(struct repository *repo,
@@ -583,6 +599,9 @@ int git_config_get_value(const char *key, const char **value);
 RESULT_MUST_BE_USED
 int git_config_get_value_multi(const char *key,
 			       const struct string_list **dest);
+RESULT_MUST_BE_USED
+int git_config_get_string_multi(const char *key,
+				const struct string_list **dest);
 
 /**
  * Resets and invalidates the config cache.
diff --git a/pack-bitmap.c b/pack-bitmap.c
index 81f0c0e016..dd05ab03ca 100644
--- a/pack-bitmap.c
+++ b/pack-bitmap.c
@@ -2303,7 +2303,7 @@ const struct string_list *bitmap_preferred_tips(struct repository *r)
 {
 	const struct string_list *dest;
 
-	if (!repo_config_get_value_multi(r, "pack.preferbitmaptips", &dest))
+	if (!repo_config_get_string_multi(r, "pack.preferbitmaptips", &dest))
 		return dest;
 	return NULL;
 }
diff --git a/submodule.c b/submodule.c
index e43c4230ba..0f6cf864ed 100644
--- a/submodule.c
+++ b/submodule.c
@@ -274,7 +274,7 @@ int is_tree_submodule_active(struct repository *repo,
 	free(key);
 
 	/* submodule.active is set */
-	if (!repo_config_get_value_multi(repo, "submodule.active", &sl)) {
+	if (!repo_config_get_string_multi(repo, "submodule.active", &sl)) {
 		struct pathspec ps;
 		struct strvec args = STRVEC_INIT;
 		const struct string_list_item *item;
diff --git a/t/t4202-log.sh b/t/t4202-log.sh
index e4f02d8208..ae73aef922 100755
--- a/t/t4202-log.sh
+++ b/t/t4202-log.sh
@@ -835,7 +835,7 @@ test_expect_success 'log.decorate configuration' '
 
 '
 
-test_expect_failure 'parse log.excludeDecoration with no value' '
+test_expect_success 'parse log.excludeDecoration with no value' '
 	cp .git/config .git/config.orig &&
 	test_when_finished mv .git/config.orig .git/config &&
 
@@ -843,7 +843,11 @@ test_expect_failure 'parse log.excludeDecoration with no value' '
 	[log]
 		excludeDecoration
 	EOF
-	git log --decorate=short
+	cat >expect <<-\EOF &&
+	error: missing value for '\''log.excludeDecoration'\''
+	EOF
+	git log --decorate=short 2>actual &&
+	test_cmp expect actual
 '
 
 test_expect_success 'decorate-refs with glob' '
diff --git a/t/t5310-pack-bitmaps.sh b/t/t5310-pack-bitmaps.sh
index 2e65c8139c..894c750080 100755
--- a/t/t5310-pack-bitmaps.sh
+++ b/t/t5310-pack-bitmaps.sh
@@ -404,7 +404,7 @@ test_bitmap_cases () {
 		)
 	'
 
-	test_expect_failure 'pack.preferBitmapTips' '
+	test_expect_success 'pack.preferBitmapTips' '
 		git init repo &&
 		test_when_finished "rm -rf repo" &&
 		(
@@ -416,7 +416,11 @@ test_bitmap_cases () {
 			[pack]
 				preferBitmapTips
 			EOF
-			git repack -adb
+			cat >expect <<-\EOF &&
+			error: missing value for '\''pack.preferbitmaptips'\''
+			EOF
+			git repack -adb 2>actual &&
+			test_cmp expect actual
 		)
 	'
 
diff --git a/t/t7004-tag.sh b/t/t7004-tag.sh
index f343551a7d..f4a31ada79 100755
--- a/t/t7004-tag.sh
+++ b/t/t7004-tag.sh
@@ -1843,7 +1843,7 @@ test_expect_success 'invalid sort parameter in configuratoin' '
 	test_must_fail git tag -l "foo*"
 '
 
-test_expect_failure 'version sort handles empty value for versionsort.{prereleaseSuffix,suffix}' '
+test_expect_success 'version sort handles empty value for versionsort.{prereleaseSuffix,suffix}' '
 	cp .git/config .git/config.orig &&
 	test_when_finished mv .git/config.orig .git/config &&
 
@@ -1852,7 +1852,12 @@ test_expect_failure 'version sort handles empty value for versionsort.{prereleas
 		prereleaseSuffix
 		suffix
 	EOF
-	git tag -l --sort=version:refname
+	cat >expect <<-\EOF &&
+	error: missing value for '\''versionsort.suffix'\''
+	error: missing value for '\''versionsort.prereleasesuffix'\''
+	EOF
+	git tag -l --sort=version:refname 2>actual &&
+	test_cmp expect actual
 '
 
 test_expect_success 'version sort with prerelease reordering' '
diff --git a/t/t7413-submodule-is-active.sh b/t/t7413-submodule-is-active.sh
index bfe27e5073..887d181b72 100755
--- a/t/t7413-submodule-is-active.sh
+++ b/t/t7413-submodule-is-active.sh
@@ -51,7 +51,7 @@ test_expect_success 'is-active works with submodule.<name>.active config' '
 	test-tool -C super submodule is-active sub1
 '
 
-test_expect_failure 'is-active handles submodule.active config missing a value' '
+test_expect_success 'is-active handles submodule.active config missing a value' '
 	cp super/.git/config super/.git/config.orig &&
 	test_when_finished mv super/.git/config.orig super/.git/config &&
 
@@ -60,7 +60,11 @@ test_expect_failure 'is-active handles submodule.active config missing a value'
 		active
 	EOF
 
-	test-tool -C super submodule is-active sub1
+	cat >expect <<-\EOF &&
+	error: missing value for '\''submodule.active'\''
+	EOF
+	test-tool -C super submodule is-active sub1 2>actual &&
+	test_cmp expect actual
 '
 
 test_expect_success 'is-active works with basic submodule.active config' '
diff --git a/t/t7900-maintenance.sh b/t/t7900-maintenance.sh
index d82eac6a47..487e326b3f 100755
--- a/t/t7900-maintenance.sh
+++ b/t/t7900-maintenance.sh
@@ -524,7 +524,7 @@ test_expect_success 'register and unregister' '
 	git maintenance unregister --config-file ./other --force
 '
 
-test_expect_failure 'register with no value for maintenance.repo' '
+test_expect_success 'register with no value for maintenance.repo' '
 	cp .git/config .git/config.orig &&
 	test_when_finished mv .git/config.orig .git/config &&
 
@@ -532,10 +532,15 @@ test_expect_failure 'register with no value for maintenance.repo' '
 	[maintenance]
 		repo
 	EOF
-	git maintenance register
+	cat >expect <<-\EOF &&
+	error: missing value for '\''maintenance.repo'\''
+	EOF
+	git maintenance register 2>actual &&
+	test_cmp expect actual &&
+	git config maintenance.repo
 '
 
-test_expect_failure 'unregister with no value for maintenance.repo' '
+test_expect_success 'unregister with no value for maintenance.repo' '
 	cp .git/config .git/config.orig &&
 	test_when_finished mv .git/config.orig .git/config &&
 
@@ -543,8 +548,18 @@ test_expect_failure 'unregister with no value for maintenance.repo' '
 	[maintenance]
 		repo
 	EOF
-	git maintenance unregister &&
-	git maintenance unregister --force
+	cat >expect <<-\EOF &&
+	error: missing value for '\''maintenance.repo'\''
+	EOF
+	test_expect_code 128 git maintenance unregister 2>actual.raw &&
+	grep ^error actual.raw >actual &&
+	test_cmp expect actual &&
+	git config maintenance.repo &&
+
+	git maintenance unregister --force 2>actual.raw &&
+	grep ^error actual.raw >actual &&
+	test_cmp expect actual &&
+	git config maintenance.repo
 '
 
 test_expect_success !MINGW 'register and unregister with regex metacharacters' '
diff --git a/versioncmp.c b/versioncmp.c
index 60c3a51712..7498da96e0 100644
--- a/versioncmp.c
+++ b/versioncmp.c
@@ -164,8 +164,8 @@ int versioncmp(const char *s1, const char *s2)
 		const char *const oldk = "versionsort.prereleasesuffix";
 		const struct string_list *newl;
 		const struct string_list *oldl;
-		int new = git_config_get_value_multi(newk, &newl);
-		int old = git_config_get_value_multi(oldk, &oldl);
+		int new = git_config_get_string_multi(newk, &newl);
+		int old = git_config_get_string_multi(oldk, &oldl);
 
 		if (!new && !old)
 			warning("ignoring %s because %s is set", oldk, newk);