Patch "tcp/dccp: fix lockdep splat in inet_csk_route_req()" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

tcp/dccp: fix lockdep splat in inet_csk_route_req()

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
tcp-dccp-fix-lockdep-splat-in-inet_csk_route_req.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Eric Dumazet <[email protected]>
Date: Sun, 22 Oct 2017 12:33:57 -0700
Subject: tcp/dccp: fix lockdep splat in inet_csk_route_req()

From: Eric Dumazet <[email protected]>

[ Upstream commit a6ca7abe53633d08eea1c6756cb49c9b2d4c90bf ]

This patch fixes the following lockdep splat in inet_csk_route_req()

lockdep_rcu_suspicious
inet_csk_route_req
tcp_v4_send_synack
tcp_rtx_synack
inet_rtx_syn_ack
tcp_fastopen_synack_time
tcp_retransmit_timer
tcp_write_timer_handler
tcp_write_timer
call_timer_fn

Thread running inet_csk_route_req() owns a reference on the request socket, so we have the guarantee ireq->ireq_opt wont be changed or freed.

lockdep can enforce this invariant for us.

---
 net/ipv4/inet_connection_sock.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

@@ -410,7 +410,8 @@ struct dst_entry *inet_csk_route_req(con
 	struct ip_options_rcu *opt;
 	struct rtable *rt;
 
-	opt = rcu_dereference(ireq->ireq_opt);
+	opt = rcu_dereference_protected(ireq->ireq_opt,
+					atomic_read(&req->rsk_refcnt) > 0);
 	flowi4_init_output(fl4, ireq->ir_iif, ireq->ir_mark,
 			   RT_CONN_FLAGS(sk), RT_SCOPE_UNIVERSE,
 			   sk->sk_protocol, inet_sk_flowi_flags(sk),

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/net-call-cgroup_sk_alloc-earlier-in-sk_clone_lock.patch queue-4.9/tcp-dccp-fix-ireq-opt-races.patch queue-4.9/tcp-fix-tcp_mtu_probe-vs-highest_sack.patch queue-4.9/ipv6-addrconf-increment-ifp-refcount-before-ipv6_del_addr.patch queue-4.9/ipv6-flowlabel-do-not-leave-opt-tot_len-with-garbage.patch queue-4.9/packet-avoid-panic-in-packet_getsockopt.patch queue-4.9/sctp-add-the-missing-sock_owned_by_user-check-in-sctp_icmp_redirect.patch queue-4.9/net_sched-avoid-matching-qdisc-with-zero-handle.patch queue-4.9/tun-tap-sanitize-tunsetsndbuf-input.patch queue-4.9/tcp-dccp-fix-lockdep-splat-in-inet_csk_route_req.patch queue-4.9/tcp-dccp-fix-other-lockdep-splats-accessing-ireq_opt.patch