In the Linux kernel, the following vulnerability has been resolved:
xfrm: espintcp: fix UAF during close
ZDI reported and analyzed a race condition during close for espintcp
sockets:
<pre>
espintcp_close() frees emsg->skb via kfree_skb() without holding
any socket lock. Concurrently, the xfrm_trans_reinject work queue
invokes esp_output_tcp_finish() -> espintcp_push_skb() ->
espintcp_push_msgs() -> skb_send_sock_locked(), which reads the
same skb as a data source.
</pre>
Fix this by adding a synchronize_rcu() call after resetting sk_prot,
since esp_output_tcp_finish() runs under RCU and won't use a socket
with sk_prot == &tcp_prot. Simply taking the socket lock in
espintcp_close() could lead to leaks, if esp_output_tcp_finish()
re-adds an skb in the slot we just freed. After this, the existing
barrier() is no longer needed.