[PATCH 09/15] remote: handle NULL value for remotes.<group>

["Thomas Bachem via GitGitGadget" <gitgitgadget@gmail.com>]

From: Thomas Bachem <mail@thomasbachem.com>

A remotes.<group> without a value makes "git fetch <group>" and
"git push <group>" segfault: get_remote_group() dereferences the NULL
value as it splits the list of remotes.

Reject a missing value with config_error_nonbool(), and keep the
whole key for its message by skipping the "remotes." prefix into a
separate variable.

Assisted-by: Claude Opus 5.5
Signed-off-by: Thomas Bachem <mail@thomasbachem.com>
---
 remote.c                 | 5 ++++-
 t/t5506-remote-groups.sh | 5 +++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/remote.c b/remote.c
index 024cfc547d..4bd23ddac9 100644
--- a/remote.c
+++ b/remote.c
@@ -2191,8 +2191,11 @@ int get_remote_group(const char *key, const char *value,
 			    void *priv)
 {
 	struct remote_group_data *g = priv;
+	const char *group;
 
-	if (skip_prefix(key, "remotes.", &key) && !strcmp(key, g->name)) {
+	if (skip_prefix(key, "remotes.", &group) && !strcmp(group, g->name)) {
+		if (!value)
+			return config_error_nonbool(key);
 		/* split list by white space */
 		while (*value) {
 			size_t wordlen = strcspn(value, " \t\n");
diff --git a/t/t5506-remote-groups.sh b/t/t5506-remote-groups.sh
index 16e9a1bc2f..f11eb8511e 100755
--- a/t/t5506-remote-groups.sh
+++ b/t/t5506-remote-groups.sh
@@ -54,6 +54,11 @@ test_expect_success 'nonexistent group produces error' '
 	! repo_fetched two
 '
 
+test_expect_success 'remotes.<group> without a value is rejected' '
+	test_must_fail git -c remotes.valueless fetch valueless 2>err &&
+	test_grep "missing value for .remotes.valueless." err
+'
+
 test_expect_success 'updating group updates all members (remote update)' '
 	mark group-all &&
 	update_repos &&
-- 
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