Patch "sctp: Prevent soft lockup when sctp_accept() is called during a timeout event" has been added to the 3.14-stable tree

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

sctp: Prevent soft lockup when sctp_accept() is called during a timeout event

to the 3.14-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:
sctp-prevent-soft-lockup-when-sctp_accept-is-called-during-a-timeout-event.patch
and it can be found in the queue-3.14 subdirectory.

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

From: Karl Heiss <[email protected]>
Date: Thu, 24 Sep 2015 12:15:07 -0400
Subject: sctp: Prevent soft lockup when sctp_accept() is called during a timeout event

From: Karl Heiss <[email protected]>

commit 635682a14427d241bab7bbdeebb48a7d7b91638e upstream.

A case can occur when sctp_accept() is called by the user during a heartbeat timeout event after the 4-way handshake. Since sctp_assoc_migrate() changes both assoc->base.sk and assoc->ep, the bh_sock_lock in sctp_generate_heartbeat_event() will be taken with the listening socket but released with the new association socket. The result is a deadlock on any future attempts to take the listening socket lock.

Note that this race can occur with other SCTP timeouts that take the bh_lock_sock() in the event sctp_accept() is called.

 BUG: soft lockup - CPU#9 stuck for 67s! [swapper:0]
 ...
 RIP: 0010:[<ffffffff8152d48e>]  [<ffffffff8152d48e>] _spin_lock+0x1e/0x30
 RSP: 0018:ffff880028323b20  EFLAGS: 00000206
 RAX: 0000000000000002 RBX: ffff880028323b20 RCX: 0000000000000000
 RDX: 0000000000000000 RSI: ffff880028323be0 RDI: ffff8804632c4b48
 RBP: ffffffff8100bb93 R08: 0000000000000000 R09: 0000000000000000
 R10: ffff880610662280 R11: 0000000000000100 R12: ffff880028323aa0
 R13: ffff8804383c3880 R14: ffff880028323a90 R15: ffffffff81534225
 FS:  0000000000000000(0000) GS:ffff880028320000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0018 ES: 0018 CR0: 000000008005003b
 CR2: 00000000006df528 CR3: 0000000001a85000 CR4: 00000000000006e0
 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
 DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
 Process swapper (pid: 0, threadinfo ffff880616b70000, task ffff880616b6cab0)
 Stack:
 ffff880028323c40 ffffffffa01c2582 ffff880614cfb020 0000000000000000
 <d> 0100000000000000 00000014383a6c44 ffff8804383c3880 ffff880614e93c00
 <d> ffff880614e93c00 0000000000000000 ffff8804632c4b00 ffff8804383c38b8
 Call Trace:
 <IRQ>
 [<ffffffffa01c2582>] ? sctp_rcv+0x492/0xa10 [sctp]
 [<ffffffff8148c559>] ? nf_iterate+0x69/0xb0
 [<ffffffff814974a0>] ? ip_local_deliver_finish+0x0/0x2d0
 [<ffffffff8148c716>] ? nf_hook_slow+0x76/0x120
 [<ffffffff814974a0>] ? ip_local_deliver_finish+0x0/0x2d0
 [<ffffffff8149757d>] ? ip_local_deliver_finish+0xdd/0x2d0
 [<ffffffff81497808>] ? ip_local_deliver+0x98/0xa0
 [<ffffffff81496ccd>] ? ip_rcv_finish+0x12d/0x440
 [<ffffffff81497255>] ? ip_rcv+0x275/0x350
 [<ffffffff8145cfeb>] ? __netif_receive_skb+0x4ab/0x750
 ...

With lockdep debugging:

=====================================
[ BUG: bad unlock balance detected! ]
-------------------------------------
CslRx/12087 is trying to release lock (slock-AF_INET) at:

 [<ffffffffa01bcae0>] sctp_generate_timeout_event+0x40/0xe0 [sctp]
 but there are no more locks to release!

other info that might help us debug this:
2 locks held by CslRx/12087:
#0: (&asoc->timers[i]){+.-...}, at: [<ffffffff8108ce1f>] run_timer_softirq+0x16f/0x3e0 #1: (slock-AF_INET){+.-...}, at: [<ffffffffa01bcac3>] sctp_generate_timeout_event+0x23/0xe0 [sctp]

Ensure the socket taken is also the same one that is released by saving a copy of the socket before entering the timeout event critical section.

---
 net/sctp/sm_sideeffect.c |   42 +++++++++++++++++++++++-------------------
 1 file changed, 23 insertions(+), 19 deletions(-)

@@ -244,12 +244,13 @@ void sctp_generate_t3_rtx_event(unsigned
 	int error;
 	struct sctp_transport *transport = (struct sctp_transport *) peer;
 	struct sctp_association *asoc = transport->asoc;
-	struct net *net = sock_net(asoc->base.sk);
+	struct sock *sk = asoc->base.sk;
+	struct net *net = sock_net(sk);
 
 	/* Check whether a task is in the sock.  */
 
-	bh_lock_sock(asoc->base.sk);
-	if (sock_owned_by_user(asoc->base.sk)) {
+	bh_lock_sock(sk);
+	if (sock_owned_by_user(sk)) {
 		pr_debug("%s: sock is busy\n", __func__);
 
 		/* Try again later.  */

@@ -272,10 +273,10 @@ void sctp_generate_t3_rtx_event(unsigned
 			   transport, GFP_ATOMIC);
 
 	if (error)
-		asoc->base.sk->sk_err = -error;
+		sk->sk_err = -error;
 
 out_unlock:
-	bh_unlock_sock(asoc->base.sk);
+	bh_unlock_sock(sk);
 	sctp_transport_put(transport);
 }
 

@@ -285,11 +286,12 @@ out_unlock:
 static void sctp_generate_timeout_event(struct sctp_association *asoc,
 					sctp_event_timeout_t timeout_type)
 {
-	struct net *net = sock_net(asoc->base.sk);
+	struct sock *sk = asoc->base.sk;
+	struct net *net = sock_net(sk);
 	int error = 0;
 
-	bh_lock_sock(asoc->base.sk);
-	if (sock_owned_by_user(asoc->base.sk)) {
+	bh_lock_sock(sk);
+	if (sock_owned_by_user(sk)) {
 		pr_debug("%s: sock is busy: timer %d\n", __func__,
 			 timeout_type);
 

@@ -312,10 +314,10 @@ static void sctp_generate_timeout_event(
 			   (void *)timeout_type, GFP_ATOMIC);
 
 	if (error)
-		asoc->base.sk->sk_err = -error;
+		sk->sk_err = -error;
 
 out_unlock:
-	bh_unlock_sock(asoc->base.sk);
+	bh_unlock_sock(sk);
 	sctp_association_put(asoc);
 }
 

@@ -365,10 +367,11 @@ void sctp_generate_heartbeat_event(unsig
 	int error = 0;
 	struct sctp_transport *transport = (struct sctp_transport *) data;
 	struct sctp_association *asoc = transport->asoc;
-	struct net *net = sock_net(asoc->base.sk);
+	struct sock *sk = asoc->base.sk;
+	struct net *net = sock_net(sk);
 
-	bh_lock_sock(asoc->base.sk);
-	if (sock_owned_by_user(asoc->base.sk)) {
+	bh_lock_sock(sk);
+	if (sock_owned_by_user(sk)) {
 		pr_debug("%s: sock is busy\n", __func__);
 
 		/* Try again later.  */

@@ -389,10 +392,10 @@ void sctp_generate_heartbeat_event(unsig
 			   transport, GFP_ATOMIC);
 
 	 if (error)
-		 asoc->base.sk->sk_err = -error;
+		sk->sk_err = -error;
 
 out_unlock:
-	bh_unlock_sock(asoc->base.sk);
+	bh_unlock_sock(sk);
 	sctp_transport_put(transport);
 }
 

@@ -403,10 +406,11 @@ void sctp_generate_proto_unreach_event(u
 {
 	struct sctp_transport *transport = (struct sctp_transport *) data;
 	struct sctp_association *asoc = transport->asoc;
-	struct net *net = sock_net(asoc->base.sk);
+	struct sock *sk = asoc->base.sk;
+	struct net *net = sock_net(sk);
 
-	bh_lock_sock(asoc->base.sk);
-	if (sock_owned_by_user(asoc->base.sk)) {
+	bh_lock_sock(sk);
+	if (sock_owned_by_user(sk)) {
 		pr_debug("%s: sock is busy\n", __func__);
 
 		/* Try again later.  */

@@ -427,7 +431,7 @@ void sctp_generate_proto_unreach_event(u
 		   asoc->state, asoc->ep, asoc, transport, GFP_ATOMIC);
 
 out_unlock:
-	bh_unlock_sock(asoc->base.sk);
+	bh_unlock_sock(sk);
 	sctp_association_put(asoc);
 }
 

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

queue-3.14/sctp-prevent-soft-lockup-when-sctp_accept-is-called-during-a-timeout-event.patch