In the Linux kernel, the following vulnerability has been resolved:
rds: drop incoming messages that cross network namespace boundaries
rds_find_bound() looks up the destination socket using a global rhashtable keyed solely on (addr, port, scope_id). Network namespaces are not part of the key, so a sender in netns A can deliver an incoming message (inc) to a socket that lives in a different netns B.
When this happens, inc->i_conn points to an rds_connection whose c_net is netns A, but the receiving rs lives in netns B. Once the child process that created netns A exits, cleanup_net() calls rds_loop_exit_net() -> rds_loop_kill_conns() -> rds_conn_destroy(), freeing that connection. If the survivor socket in netns B still holds the inc, any subsequent dereference of inc->i_conn is a use-after-free.
There are two dangerous sites in rds_clear_recv_queue():
- inc->i_conn->c_lcong (offset 88 of freed rds_connection, size 200)
- inc->i_conn->c_trans->inc_free(inc) (function pointer at offset 80)
The bug is reachable from unprivileged user namespaces (CLONE_NEWUSER + CLONE_NEWNET), available since Linux 3.8.
Fix this by rejecting the delivery in rds_recv_incoming() when the socket returned by rds_find_bound() belongs to a different network namespace than the connection that carried the message. Use the existing rds_conn_net() / sock_net() helpers and net_eq() for the comparison.