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: 4f0087812648 ("sctp: apply rhashtable api to send/recv path")
Reported-by: Vlad Yasevich <vyasevich@gmail.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Signed-off-by: Marcelo Ricardo Leitner <marcelo.leitner@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
index 20e7212..344da04 100644
--- a/include/net/sctp/structs.h
+++ b/include/net/sctp/structs.h
@@ -955,7 +955,7 @@
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);
diff --git a/net/sctp/input.c b/net/sctp/input.c
index bf61dfb..49d2cc7 100644
--- a/net/sctp/input.c
+++ b/net/sctp/input.c
@@ -935,15 +935,22 @@
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 *asoc;
- rcu_read_lock();
asoc = __sctp_lookup_association(net, laddr, paddr, transportp);
- rcu_read_unlock();
return asoc;
}
diff --git a/net/sctp/transport.c b/net/sctp/transport.c
index aab9e3f..69f3799 100644
--- a/net/sctp/transport.c
+++ b/net/sctp/transport.c
@@ -296,9 +296,9 @@
}
/* 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