Replace CMSG !/cred/prefix with !/cred/whoami

Signed-off-by: Mattias Andrée <maandree@kth.se>

3 files changed, 38 insertions, 27 deletions

diff --git a/README b/README
index 1464186..b538c68 100644
--- a/README
+++ b/README
@@ -120,13 +120,17 @@ Secret messages:
 
 	However, due to network support, these routing keys may need
 	to be prefixed with the credentials for the servers the message
-	goes through. This prefix can be retrieved by simply sending an
-	empty control message (CMSG) with the routing key '!/cred/prefix'
-	and the server will reply with a control message containing prefix
-	using this routing key. Note, prefix is probably the empty string,
-	as the master server do not need to add its credentials to be
-	prefixed. Note, the server will never send control messages, so
-	received control message are guaranteed to come from the server.
+	goes through, or use the credentials of the a program running
+	on a different master machine. Therefore, a client cannot
+	simply just use its GID, UID, and PID, but must ask what's its
+	credentials are by sending an empty control message (CMSG) with
+	the routing key '!/cred/whoami'. The server will reply with a
+	control message with the same routing key and the message will
+	be the credentials, for example '!/cred/100/1000/1111' or
+	'!/cred/100/1000/1111/!/cred/1000/1000/19211'. Note, the server
+	will never send control messages it receives from other clients,
+	so the received control message is guaranteed to come from the
+	server.
 
 	Example of how two client can prove their identities to each oter:
 
diff --git a/sbusd.c b/sbusd.c
index e2f3005..b2b8e2c 100644
--- a/sbusd.c
+++ b/sbusd.c
@@ -292,36 +292,44 @@ send_packet(struct client *cl, const char *buf, size_t n)
 }
 
 static void
-handle_cmsg(struct client *cl, const char *msg, size_t n)
+handle_cmsg(struct client *cl, char *buf, size_t n)
 {
-	if (!strcmp(msg, "CMSG !/cred/prefix")) {
-		n = sizeof("CMSG !/cred/prefix");
-	} else if (!strcmp(msg, "CMSG blocking/soft/queue")) {
+	struct ucred cred;
+	if (!strcmp(buf, "CMSG !/cred/whoami")) {
+		if (getsockopt(cl->fd, SOL_SOCKET, SO_PEERCRED, &cred, &(socklen_t){sizeof(cred)}) < 0) {
+			weprintf("getsockopt <client> SOL_SOCKET SO_PEERCRED:");
+			remove_client(cl);
+			return;
+		}
+		n = sizeof("CMSG !/cred/whoami");
+		n += (size_t)sprintf(&buf[n], "!/cred/%lli/%lli/%lli",
+				     (long long int)cred.gid,
+				     (long long int)cred.uid,
+				     (long long int)cred.gid);
+		if (send_packet(cl, buf, n)) {
+			weprintf("send <client>:");
+			remove_client(cl);
+		}
+	} else if (!strcmp(buf, "CMSG blocking/soft/queue")) {
 		cl->soft_blocking_mode = BLOCKING_QUEUE;
-	} else if (!strcmp(msg, "CMSG blocking/soft/discard")) {
+	} else if (!strcmp(buf, "CMSG blocking/soft/discard")) {
 		cl->soft_blocking_mode = BLOCKING_DISCARD;
-	} else if (!strcmp(msg, "CMSG blocking/soft/block")) {
+	} else if (!strcmp(buf, "CMSG blocking/soft/block")) {
 		cl->soft_blocking_mode = BLOCKING_BLOCK;
-	} else if (!strcmp(msg, "CMSG blocking/soft/error")) {
+	} else if (!strcmp(buf, "CMSG blocking/soft/error")) {
 		cl->soft_blocking_mode = BLOCKING_ERROR;
-	} else if (!strcmp(msg, "CMSG blocking/hard/discard")) {
+	} else if (!strcmp(buf, "CMSG blocking/hard/discard")) {
 		cl->hard_blocking_mode = BLOCKING_DISCARD;
-	} else if (!strcmp(msg, "CMSG blocking/hard/block")) {
+	} else if (!strcmp(buf, "CMSG blocking/hard/block")) {
 		cl->hard_blocking_mode = BLOCKING_BLOCK;
-	} else if (!strcmp(msg, "CMSG blocking/hard/error")) {
+	} else if (!strcmp(buf, "CMSG blocking/hard/error")) {
 		cl->hard_blocking_mode = BLOCKING_ERROR;
-	} else if (!strcmp(msg, "CMSG order/queue")) {
+	} else if (!strcmp(buf, "CMSG order/queue")) {
 		cl->order = ORDER_QUEUE;
-	} else if (!strcmp(msg, "CMSG order/stack")) {
+	} else if (!strcmp(buf, "CMSG order/stack")) {
 		cl->order = ORDER_STACK;
-	} else if (!strcmp(msg, "CMSG order/random")) {
+	} else if (!strcmp(buf, "CMSG order/random")) {
 		cl->order |= ORDER_RANDOM;
-	} else {
-		return;
-	}
-	if (send_packet(cl, msg, n)) {
-		weprintf("send <client>:");
-		remove_client(cl);
 	}
 }
 
diff --git a/test.c b/test.c
index daaec35..c2ba2a8 100644
--- a/test.c
+++ b/test.c
@@ -355,4 +355,3 @@ main(void)
 
 /* TODO untested sbusd flags: -p[/dev/null] (-f) -u */
 /* TODO test credentials */
-/* TODO test CMSG server */