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Subject[PATCH 3.2 83/87] sctp: Prevent soft lockup when sctp_accept() is called during a timeout event
3.2.77-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Karl Heiss <kheiss@gmail.com>

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.

Signed-off-by: Karl Heiss <kheiss@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.2:
- Net namespaces are not used
- Keep using sctp_bh_{,un}lock_sock()
- Adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/net/sctp/sm_sideeffect.c
+++ b/net/sctp/sm_sideeffect.c
@@ -249,11 +249,12 @@ void sctp_generate_t3_rtx_event(unsigned
int error;
struct sctp_transport *transport = (struct sctp_transport *) peer;
struct sctp_association *asoc = transport->asoc;
+ struct sock *sk = asoc->base.sk;

/* Check whether a task is in the sock. */

- sctp_bh_lock_sock(asoc->base.sk);
- if (sock_owned_by_user(asoc->base.sk)) {
+ sctp_bh_lock_sock(sk);
+ if (sock_owned_by_user(sk)) {
SCTP_DEBUG_PRINTK("%s:Sock is busy.\n", __func__);

/* Try again later. */
@@ -276,10 +277,10 @@ void sctp_generate_t3_rtx_event(unsigned
transport, GFP_ATOMIC);

if (error)
- asoc->base.sk->sk_err = -error;
+ sk->sk_err = -error;

out_unlock:
- sctp_bh_unlock_sock(asoc->base.sk);
+ sctp_bh_unlock_sock(sk);
sctp_transport_put(transport);
}

@@ -289,10 +290,11 @@ out_unlock:
static void sctp_generate_timeout_event(struct sctp_association *asoc,
sctp_event_timeout_t timeout_type)
{
+ struct sock *sk = asoc->base.sk;
int error = 0;

- sctp_bh_lock_sock(asoc->base.sk);
- if (sock_owned_by_user(asoc->base.sk)) {
+ sctp_bh_lock_sock(sk);
+ if (sock_owned_by_user(sk)) {
SCTP_DEBUG_PRINTK("%s:Sock is busy: timer %d\n",
__func__,
timeout_type);
@@ -316,10 +318,10 @@ 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:
- sctp_bh_unlock_sock(asoc->base.sk);
+ sctp_bh_unlock_sock(sk);
sctp_association_put(asoc);
}

@@ -369,9 +371,10 @@ void sctp_generate_heartbeat_event(unsig
int error = 0;
struct sctp_transport *transport = (struct sctp_transport *) data;
struct sctp_association *asoc = transport->asoc;
+ struct sock *sk = asoc->base.sk;

- sctp_bh_lock_sock(asoc->base.sk);
- if (sock_owned_by_user(asoc->base.sk)) {
+ sctp_bh_lock_sock(sk);
+ if (sock_owned_by_user(sk)) {
SCTP_DEBUG_PRINTK("%s:Sock is busy.\n", __func__);

/* Try again later. */
@@ -392,10 +395,10 @@ void sctp_generate_heartbeat_event(unsig
transport, GFP_ATOMIC);

if (error)
- asoc->base.sk->sk_err = -error;
+ sk->sk_err = -error;

out_unlock:
- sctp_bh_unlock_sock(asoc->base.sk);
+ sctp_bh_unlock_sock(sk);
sctp_transport_put(transport);
}

@@ -406,9 +409,10 @@ void sctp_generate_proto_unreach_event(u
{
struct sctp_transport *transport = (struct sctp_transport *) data;
struct sctp_association *asoc = transport->asoc;
+ struct sock *sk = asoc->base.sk;

- sctp_bh_lock_sock(asoc->base.sk);
- if (sock_owned_by_user(asoc->base.sk)) {
+ sctp_bh_lock_sock(sk);
+ if (sock_owned_by_user(sk)) {
SCTP_DEBUG_PRINTK("%s:Sock is busy.\n", __func__);

/* Try again later. */
@@ -429,7 +433,7 @@ void sctp_generate_proto_unreach_event(u
asoc->state, asoc->ep, asoc, transport, GFP_ATOMIC);

out_unlock:
- sctp_bh_unlock_sock(asoc->base.sk);
+ sctp_bh_unlock_sock(sk);
sctp_association_put(asoc);
}

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