receive-pack: verify push options in cert

In commit f6a4e61 ("push: accept push options", 2016-07-14), send-pack
was taught to include push options both within the signed cert (if the
push is a signed push) and outside the signed cert; however,
receive-pack ignores push options within the cert, only handling push
options outside the cert.

Teach receive-pack, in the case that push options are provided for a
signed push, to verify that the push options both within the cert and
outside the cert are consistent.

This sets in stone the requirement that send-pack redundantly send its
push options in 2 places, but I think that this is better than the
alternatives. Sending push options only within the cert is
backwards-incompatible with existing Git servers (which read push
options only from outside the cert), and sending push options only
outside the cert means that the push options are not signed for.

Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 49 insertions, 2 deletions

diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index b618d52139..ed21142349 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -470,7 +470,8 @@ static char *prepare_push_cert_nonce(const char *path, unsigned long stamp)
  * after dropping "_commit" from its name and possibly moving it out
  * of commit.c
  */
-static char *find_header(const char *msg, size_t len, const char *key)
+static char *find_header(const char *msg, size_t len, const char *key,
+			 const char **next_line)
 {
 	int key_len = strlen(key);
 	const char *line = msg;
@@ -483,6 +484,8 @@ static char *find_header(const char *msg, size_t len, const char *key)
 		if (line + key_len < eol &&
 		    !memcmp(line, key, key_len) && line[key_len] == ' ') {
 			int offset = key_len + 1;
+			if (next_line)
+				*next_line = *eol ? eol + 1 : eol;
 			return xmemdupz(line + offset, (eol - line) - offset);
 		}
 		line = *eol ? eol + 1 : NULL;
@@ -492,7 +495,7 @@ static char *find_header(const char *msg, size_t len, const char *key)
 
 static const char *check_nonce(const char *buf, size_t len)
 {
-	char *nonce = find_header(buf, len, "nonce");
+	char *nonce = find_header(buf, len, "nonce", NULL);
 	unsigned long stamp, ostamp;
 	char *bohmac, *expect = NULL;
 	const char *retval = NONCE_BAD;
@@ -572,6 +575,45 @@ leave:
 	return retval;
 }
 
+/*
+ * Return 1 if there is no push_cert or if the push options in push_cert are
+ * the same as those in the argument; 0 otherwise.
+ */
+static int check_cert_push_options(const struct string_list *push_options)
+{
+	const char *buf = push_cert.buf;
+	int len = push_cert.len;
+
+	char *option;
+	const char *next_line;
+	int options_seen = 0;
+
+	int retval = 1;
+
+	if (!len)
+		return 1;
+
+	while ((option = find_header(buf, len, "push-option", &next_line))) {
+		len -= (next_line - buf);
+		buf = next_line;
+		options_seen++;
+		if (options_seen > push_options->nr
+		    || strcmp(option,
+			      push_options->items[options_seen - 1].string)) {
+			retval = 0;
+			goto leave;
+		}
+		free(option);
+	}
+
+	if (options_seen != push_options->nr)
+		retval = 0;
+
+leave:
+	free(option);
+	return retval;
+}
+
 static void prepare_push_cert_sha1(struct child_process *proc)
 {
 	static int already_done;
@@ -1924,6 +1966,11 @@ int cmd_receive_pack(int argc, const char **argv, const char *prefix)
 
 		if (use_push_options)
 			read_push_options(&push_options);
+		if (!check_cert_push_options(&push_options)) {
+			struct command *cmd;
+			for (cmd = commands; cmd; cmd = cmd->next)
+				cmd->error_string = "inconsistent push options";
+		}
 
 		prepare_shallow_info(&si, &shallow);
 		if (!si.nr_ours && !si.nr_theirs)