[PATCH net] sctp: sctp_epaddr_lookup_transport should be protected by rcu_read_lock

[Xin Long]

Since commit 7fda702f9315 ("sctp: use new rhlist interface on sctp transport
rhashtable"), sctp has changed to use rhlist_lookup to look up transport, but
rhlist_lookup doesn't call rcu_read_lock inside, unlike rhashtable_lookup_fast.

It is called in sctp_epaddr_lookup_transport and sctp_addrs_lookup_transport.
sctp_addrs_lookup_transport is always in the protection of rcu_read_lock(),
as __sctp_lookup_association is called in rx path or sctp_lookup_association
which are in the protection of rcu_read_lock() already.

But sctp_epaddr_lookup_transport is called by sctp_endpoint_lookup_assoc, it
doesn't call rcu_read_lock, which may cause "suspicious rcu_dereference_check
usage' in __rhashtable_lookup.

This patch is to fix it by adding rcu_read_lock in sctp_endpoint_lookup_assoc
before calling sctp_epaddr_lookup_transport.

Fixes: 7fda702f9315 ("sctp: use new rhlist interface on sctp transport 
rhashtable")
Reported-by: Dmitry Vyukov <dvyu...@google.com>
Signed-off-by: Xin Long <lucien....@gmail.com>
---
 net/sctp/endpointola.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/sctp/endpointola.c b/net/sctp/endpointola.c
index 1f03065..410ddc1 100644
--- a/net/sctp/endpointola.c
+++ b/net/sctp/endpointola.c
@@ -331,7 +331,9 @@ struct sctp_association *sctp_endpoint_lookup_assoc(
         * on this endpoint.
         */
        if (!ep->base.bind_addr.port)
-               goto out;
+               return NULL;
+
+       rcu_read_lock();
        t = sctp_epaddr_lookup_transport(ep, paddr);
        if (!t)
                goto out;
@@ -339,6 +341,7 @@ struct sctp_association *sctp_endpoint_lookup_assoc(
        *transport = t;
        asoc = t->asoc;
 out:
+       rcu_read_unlock();
        return asoc;
 }
 
-- 
2.1.0