Subject: [RFC PATCH] sctp: Fix a race between ICMP protocol unreachable and connect()

From: Vlad Yasevich <[email-masked]>
Date: Fri, 30 Apr 2010 21:22:50 -0400

ICMP protocol unreachable handling completely disregarded
the fact that the user may have locked the socket.  It proceeded
to destroy the association, even though the user may have
held the lock and had a ref on the association.  This resulted
in the following bug:

Attempt to release alive inet socket f6afcc00

=========================
[ BUG: held lock freed! ]
-------------------------
somenu/2672 is freeing memory f6afcc00-f6afcfff, with a lock still held
there!
 (sk_lock-AF_INET){+.+.+.}, at: [<c122098a>] sctp_connect+0x13/0x4c
1 lock held by somenu/2672:
 #0:  (sk_lock-AF_INET){+.+.+.}, at: [<c122098a>] sctp_connect+0x13/0x4c

stack backtrace:
Pid: 2672, comm: somenu Not tainted 2.6.32-telco #55
Call Trace:
 [<c1232266>] ? printk+0xf/0x11
 [<c1038553>] debug_check_no_locks_freed+0xce/0xff
 [<c10620b4>] kmem_cache_free+0x21/0x66
 [<c1185f25>] __sk_free+0x9d/0xab
 [<c1185f9c>] sk_free+0x1c/0x1e
 [<c1216e38>] sctp_association_put+0x32/0x89
 [<c1220865>] __sctp_connect+0x36d/0x3f4
 [<c122098a>] ? sctp_connect+0x13/0x4c
 [<c102d073>] ? autoremove_wake_function+0x0/0x33
 [<c12209a8>] sctp_connect+0x31/0x4c
 [<c11d1e80>] inet_dgram_connect+0x4b/0x55
 [<c11834fa>] sys_connect+0x54/0x71
 [<c103a3a2>] ? lock_release_non_nested+0x88/0x239
 [<c1054026>] ? might_fault+0x42/0x7c
 [<c1054026>] ? might_fault+0x42/0x7c
 [<c11847ab>] sys_socketcall+0x6d/0x178
 [<c10da994>] ? trace_hardirqs_on_thunk+0xc/0x10
 [<c1002959>] syscall_call+0x7/0xb

This was because the sctp_wait_for_connect() would acquire the socket
lock and then proceed to release the last reference count on the
association, thus causing the fully destruction path to finish freeing
the socket.

The simplest solution is to start a very short timer in case the socket
is owned by user.  When the timer expires, we can do some verification
and be able to do the release properly.

Signed-off-by: Vlad Yasevich <[email-masked]>
---
 include/net/sctp/sm.h      |    1 +
 include/net/sctp/structs.h |    3 +++
 net/sctp/input.c           |   23 +++++++++++++++++++----
 net/sctp/sm_sideeffect.c   |   35 +++++++++++++++++++++++++++++++++++
 net/sctp/transport.c       |    2 ++
 5 files changed, 60 insertions(+), 4 deletions(-)

diff --git a/include/net/sctp/sm.h b/include/net/sctp/sm.h
index 851c813..61d73e3 100644
--- a/include/net/sctp/sm.h
+++ b/include/net/sctp/sm.h
@@ -279,6 +279,7 @@ int sctp_do_sm(sctp_event_t event_type, sctp_subtype_t subtype,
 /* 2nd level prototypes */
 void sctp_generate_t3_rtx_event(unsigned long peer);
 void sctp_generate_heartbeat_event(unsigned long peer);
+void sctp_generate_proto_unreach_event(unsigned long peer);

 void sctp_ootb_pkt_free(struct sctp_packet *);

diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
index 597f8e2..219043a 100644
--- a/include/net/sctp/structs.h
+++ b/include/net/sctp/structs.h
@@ -1010,6 +1010,9 @@ struct sctp_transport {
 	/* Heartbeat timer is per destination. */
 	struct timer_list hb_timer;

+	/* Timer to handle ICMP proto unreachable envets */
+	struct timer_list proto_unreach_timer;
+
 	/* Since we're using per-destination retransmission timers
 	 * (see above), we're also using per-destination "transmitted"
 	 * queues.  This probably ought to be a private struct
diff --git a/net/sctp/input.c b/net/sctp/input.c
index 2a57018..94b2eb2 100644
--- a/net/sctp/input.c
+++ b/net/sctp/input.c
@@ -440,11 +440,25 @@ void sctp_icmp_proto_unreachable(struct sock *sk,
 {
 	SCTP_DEBUG_PRINTK("%s\n",  __func__);

-	sctp_do_sm(SCTP_EVENT_T_OTHER,
-		   SCTP_ST_OTHER(SCTP_EVENT_ICMP_PROTO_UNREACH),
-		   asoc->state, asoc->ep, asoc, t,
-		   GFP_ATOMIC);
+	if (sock_owned_by_user(sk)) {
+		if (timer_pending(&t->proto_unreach_timer))
+			return;
+		else {
+			if (!mod_timer(&t->proto_unreach_timer,
+						jiffies + (HZ/20)))
+				sctp_association_hold(asoc);
+		}
+			
+	} else {
+		if (timer_pending(&t->proto_unreach_timer) &&
+		    del_timer(&t->proto_unreach_timer))
+			sctp_association_put(asoc);

+		sctp_do_sm(SCTP_EVENT_T_OTHER,
+			   SCTP_ST_OTHER(SCTP_EVENT_ICMP_PROTO_UNREACH),
+			   asoc->state, asoc->ep, asoc, t,
+			   GFP_ATOMIC);
+	}
 }

 /* Common lookup code for icmp/icmpv6 error handler. */
diff --git a/net/sctp/sm_sideeffect.c b/net/sctp/sm_sideeffect.c
index d5ae450..eb1f42f 100644
--- a/net/sctp/sm_sideeffect.c
+++ b/net/sctp/sm_sideeffect.c
@@ -397,6 +397,41 @@ out_unlock:
 	sctp_transport_put(transport);
 }

+/* Handle the timeout of the ICMP protocol unreachable timer.  Trigger
+ * the correct state machine transition that will close the association.
+ */
+void sctp_generate_proto_unreach_event(unsigned long data)
+{
+	struct sctp_transport *transport = (struct sctp_transport *) data;
+	struct sctp_association *asoc = transport->asoc;
+	
+	sctp_bh_lock_sock(asoc->base.sk);
+	if (sock_owned_by_user(asoc->base.sk)) {
+		SCTP_DEBUG_PRINTK("%s:Sock is busy.\n", __func__);
+
+		/* Try again later.  */
+		if (!mod_timer(&transport->proto_unreach_timer,
+				jiffies + (HZ/20)))
+			sctp_association_hold(asoc);
+		goto out_unlock;
+	}
+
+	/* Is this structure just waiting around for us to actually
+	 * get destroyed?
+	 */
+	if (asoc->base.dead)
+		goto out_unlock;
+
+	sctp_do_sm(SCTP_EVENT_T_OTHER,
+		   SCTP_ST_OTHER(SCTP_EVENT_ICMP_PROTO_UNREACH),
+		   asoc->state, asoc->ep, asoc, transport, GFP_ATOMIC);
+
+out_unlock:
+	sctp_bh_unlock_sock(asoc->base.sk);
+	sctp_association_put(asoc);
+}
+
+
 /* Inject a SACK Timeout event into the state machine.  */
 static void sctp_generate_sack_event(unsigned long data)
 {
diff --git a/net/sctp/transport.c b/net/sctp/transport.c
index be4d63d..4a36803 100644
--- a/net/sctp/transport.c
+++ b/net/sctp/transport.c
@@ -108,6 +108,8 @@ static struct sctp_transport *sctp_transport_init(struct
sctp_transport *peer,
 			(unsigned long)peer);
 	setup_timer(&peer->hb_timer, sctp_generate_heartbeat_event,
 			(unsigned long)peer);
+	setup_timer(&peer->proto_unreach_timer,
+		    sctp_generate_proto_unreach_event, (unsigned long)peer);

 	/* Initialize the 64-bit random nonce sent with heartbeat. */
 	get_random_bytes(&peer->hb_nonce, sizeof(peer->hb_nonce));
-- 
1.6.0.4