sd-bus: if we receive an invalid dbus message, ignore and proceeed

dbus-daemon might have a slightly different idea of what a valid msg is
than us (for example regarding valid msg and field sizes). Let's hence
try to proceed if we can and thus drop messages rather than fail the
connection if we fail to validate a message.

Hopefully the differences in what is considered valid are not visible
for real-life usecases, but are specific to exploit attempts only.

(cherry-picked from commit 6d586a13717ae057aa1b4127400c3de61cd5b9e7)

Related: #1678641

diff --git a/src/libsystemd/sd-bus/bus-socket.c b/src/libsystemd/sd-bus/bus-socket.c
index a5513d1ab5f415d9d330953f7af46818771e2bdd..17cfa8e1fd56013ab19c2614b2af38457e7341a0 100644 (file)
--- a/src/libsystemd/sd-bus/bus-socket.c
+++ b/src/libsystemd/sd-bus/bus-socket.c
@@ -1078,7 +1078,7 @@ static int bus_socket_read_message_need(sd_bus *bus, size_t *need) {
 }
 
 static int bus_socket_make_message(sd_bus *bus, size_t size) {
-        sd_bus_message *t;
+        sd_bus_message *t = NULL;
         void *b;
         int r;
 
@@ -1103,7 +1103,9 @@ static int bus_socket_make_message(sd_bus *bus, size_t size) {
                                     bus->fds, bus->n_fds,
                                     NULL,
                                     &t);
-        if (r < 0) {
+        if (r == -EBADMSG)
+                log_debug_errno(r, "Received invalid message from connection %s, dropping.", strna(bus->description));
+        else if (r < 0) {
                 free(b);
                 return r;
         }
@@ -1114,7 +1116,8 @@ static int bus_socket_make_message(sd_bus *bus, size_t size) {
         bus->fds = NULL;
         bus->n_fds = 0;
 
-        bus->rqueue[bus->rqueue_size++] = t;
+        if (t)
+                bus->rqueue[bus->rqueue_size++] = t;
 
         return 1;
 }