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():
  1. inc->i_conn->c_lcong (offset 88 of freed rds_connection, size 200)
     read via rds_recv_rcvbuf_delta() -- confirmed by KASAN.
  2. inc->i_conn->c_trans->inc_free(inc) (function pointer at offset 80)
     called via rds_inc_put() when the inc refcount reaches zero -- same
     race window, potential call-through-freed-object primitive.

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.