net: fix a race in dst_release()

Orabug: 22623844

[ Upstream commit d69bbf88c8d0b367cf3e3a052f6daadf630ee566 ]

Only cpu seeing dst refcount going to 0 can safely
dereference dst->flags.

Otherwise an other cpu might already have freed the dst.

Fixes: 27b75c95f10d ("net: avoid RCU for NOCACHE dst")
Reported-by: Greg Thelen <gthelen@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit e6fac8c7fff3d816729ad16327837ba3216d48c9)
Signed-off-by: Dan Duval <dan.duval@oracle.com>

diff --git a/net/core/dst.c b/net/core/dst.c
index e956ce6d13782f2da0a229cabafef663665159eb..f8db4032d45a40aef8083550432548e8fa4e4f4f 100644 (file)
--- a/net/core/dst.c
+++ b/net/core/dst.c
@@ -285,7 +285,7 @@ void dst_release(struct dst_entry *dst)
 
                newrefcnt = atomic_dec_return(&dst->__refcnt);
                WARN_ON(newrefcnt < 0);
-               if (unlikely(dst->flags & DST_NOCACHE) && !newrefcnt)
+               if (!newrefcnt && unlikely(dst->flags & DST_NOCACHE))
                        call_rcu(&dst->rcu_head, dst_destroy_rcu);
        }
 }