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Commit 1eed6779 authored by Xin Long's avatar Xin Long Committed by David S. Miller
Browse files

sctp: fix the transport dead race check by using atomic_add_unless on refcnt 



Now when __sctp_lookup_association is running in BH, it will try to
check if t->dead is set, but meanwhile other CPUs may be freeing this
transport and this assoc and if it happens that
__sctp_lookup_association checked t->dead a bit too early, it may think
that the association is still good while it was already freed.

So we fix this race by using atomic_add_unless in sctp_transport_hold.
After we get one transport from hashtable, we will hold it only when
this transport's refcnt is not 0, so that we can make sure t->asoc
cannot be freed before we hold the asoc again.

Note that sctp association is not freed using RCU so we can't use
atomic_add_unless() with it as it may just be too late for that either.

Fixes: 4f008781 ("sctp: apply rhashtable api to send/recv path")
Reported-by: default avatarVlad Yasevich <vyasevich@gmail.com>
Signed-off-by: default avatarXin Long <lucien.xin@gmail.com>
Signed-off-by: default avatarMarcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 2baaa2d1

include/net/sctp/structs.h

+1 −1
Original line number Diff line number Diff line
@@ -955,7 +955,7 @@ void sctp_transport_route(struct sctp_transport *, union sctp_addr *, 
void sctp_transport_pmtu(struct sctp_transport *, struct sock *sk);

void sctp_transport_free(struct sctp_transport *);

void sctp_transport_reset_timers(struct sctp_transport *);

void sctp_transport_hold(struct sctp_transport *);

int sctp_transport_hold(struct sctp_transport *);

void sctp_transport_put(struct sctp_transport *);

void sctp_transport_update_rto(struct sctp_transport *, __u32);

void sctp_transport_raise_cwnd(struct sctp_transport *, __u32, __u32);

net/sctp/input.c

+11 −6
Original line number Diff line number Diff line
@@ -935,15 +935,22 @@ static struct sctp_association *__sctp_lookup_association( 
					struct sctp_transport **pt)

{

	struct sctp_transport *t;

	struct sctp_association *asoc = NULL;



	rcu_read_lock();

	t = sctp_addrs_lookup_transport(net, local, peer);

	if (!t || t->dead)

		return NULL;

	if (!t || !sctp_transport_hold(t))

		goto out;



	sctp_association_hold(t->asoc);

	asoc = t->asoc;

	sctp_association_hold(asoc);

	*pt = t;



	return t->asoc;

	sctp_transport_put(t);



out:

	rcu_read_unlock();

	return asoc;

}



/* Look up an association. protected by RCU read lock */
@@ -955,9 +962,7 @@ struct sctp_association *sctp_lookup_association(struct net *net, 
{

	struct sctp_association *asoc;



	rcu_read_lock();

	asoc = __sctp_lookup_association(net, laddr, paddr, transportp);

	rcu_read_unlock();



	return asoc;

}

net/sctp/transport.c

+2 −2
Original line number Diff line number Diff line
@@ -296,9 +296,9 @@ void sctp_transport_route(struct sctp_transport *transport, 
}



/* Hold a reference to a transport.  */

void sctp_transport_hold(struct sctp_transport *transport)

int sctp_transport_hold(struct sctp_transport *transport)

{

	atomic_inc(&transport->refcnt);

	return atomic_add_unless(&transport->refcnt, 1, 0);

}



/* Release a reference to a transport and clean up