From 1eed677933b816978abc4e3e18ecae5f254cb9be Mon Sep 17 00:00:00 2001 From: Xin Long Date: Fri, 22 Jan 2016 01:49:07 +0800 Subject: 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 Signed-off-by: Xin Long Signed-off-by: Marcelo Ricardo Leitner Signed-off-by: David S. Miller --- net/sctp/input.c | 17 +++++++++++------ 1 file changed, 11 insertions(+), 6 deletions(-) (limited to 'net/sctp/input.c') diff --git a/net/sctp/input.c b/net/sctp/input.c index bf61dfb8e09e..49d2cc751386 100644 --- a/net/sctp/input.c +++ b/net/sctp/input.c @@ -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; } -- cgit v1.2.3