fsck: handle NULL value when parsing message config

When parsing fsck.*, receive.fsck.*, or fetch.fsck.*, we don't check for
an implicit bool. So any of:

  [fsck]
  badTree
  [receive "fsck"]
  badTree
  [fetch "fsck"]
  badTree

will cause us to segfault. We can fix it with config_error_nonbool() in
the usual way, but we have to make a few more changes to get good error
messages. The problem is that all three spots do:

  if (skip_prefix(var, "fsck.", &var))

to match and parse the actual message id. But that means that "var" now
just says "badTree" instead of "receive.fsck.badTree", making the
resulting message confusing. We can fix that by storing the parsed
message id in its own separate variable.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 8 insertions, 4 deletions

diff --git a/fetch-pack.c b/fetch-pack.c
index 26999e3b65..31a72d43de 100644
--- a/fetch-pack.c
+++ b/fetch-pack.c
@@ -1862,6 +1862,8 @@ static struct ref *do_fetch_pack_v2(struct fetch_pack_args *args,
 static int fetch_pack_config_cb(const char *var, const char *value,
 				const struct config_context *ctx, void *cb)
 {
+	const char *msg_id;
+
 	if (strcmp(var, "fetch.fsck.skiplist") == 0) {
 		const char *path;
 
@@ -1873,12 +1875,14 @@ static int fetch_pack_config_cb(const char *var, const char *value,
 		return 0;
 	}
 
-	if (skip_prefix(var, "fetch.fsck.", &var)) {
-		if (is_valid_msg_type(var, value))
+	if (skip_prefix(var, "fetch.fsck.", &msg_id)) {
+		if (!value)
+			return config_error_nonbool(var);
+		if (is_valid_msg_type(msg_id, value))
 			strbuf_addf(&fsck_msg_types, "%c%s=%s",
-				fsck_msg_types.len ? ',' : '=', var, value);
+				fsck_msg_types.len ? ',' : '=', msg_id, value);
 		else
-			warning("Skipping unknown msg id '%s'", var);
+			warning("Skipping unknown msg id '%s'", msg_id);
 		return 0;
 	}