rds: drop incoming messages that cross network namespace boundaries

Overview

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.

Affected

• Linux >= c809195f5523dd4d09403bbb1c9732d548aa0d1e < 742ff6f02545212e991cd8b45011e40d2c2ef25a
• Linux >= c809195f5523dd4d09403bbb1c9732d548aa0d1e < abff41fd928328bbf3dda1140beb2e61fa424ccd
• Linux >= c809195f5523dd4d09403bbb1c9732d548aa0d1e < 03c574112e5d066df0ddce36d7438e850bcf3050
• Linux >= c809195f5523dd4d09403bbb1c9732d548aa0d1e < 1e2e2d9806944fe485824d617c8b7c78116c22db
• Linux >= c809195f5523dd4d09403bbb1c9732d548aa0d1e < cfb3ce07b705e486e022a2f2b1242b48f13981ff
• Linux >= c809195f5523dd4d09403bbb1c9732d548aa0d1e < 9591042533140dfe6608d9344806d567dcd39d02
• Linux >= c809195f5523dd4d09403bbb1c9732d548aa0d1e < 0f8690e3869109cd5803ccb400889d20a0b54e0e
• Linux >= c809195f5523dd4d09403bbb1c9732d548aa0d1e < 5521ae71e32a8069ed4ca6e792179dc57bc43ab2
• Linux c827073c95fde388bc65fe5227f944eaf859b9f0
• Linux >= 4.17.19 < 4.18
• Linux 4.18

Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.