udp: fix dst races with multicast early demux

[karo-tx-linux.git] / net / ipv4 / udp.c

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 83aa604f9273c332c5a0e5399253d961ef92eb9a..1b8c5ba7d5f732ea2220ada929049c5c7cfd5e83 100644 (file)
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1995,12 +1995,19 @@ void udp_v4_early_demux(struct sk_buff *skb)
 
        skb->sk = sk;
        skb->destructor = sock_efree;
-       dst = sk->sk_rx_dst;
+       dst = READ_ONCE(sk->sk_rx_dst);
 
        if (dst)
                dst = dst_check(dst, 0);
-       if (dst)
-               skb_dst_set_noref(skb, dst);
+       if (dst) {
+               /* DST_NOCACHE can not be used without taking a reference */
+               if (dst->flags & DST_NOCACHE) {
+                       if (likely(atomic_inc_not_zero(&dst->__refcnt)))
+                               skb_dst_set(skb, dst);
+               } else {
+                       skb_dst_set_noref(skb, dst);
+               }
+       }
 }
 
 int udp_rcv(struct sk_buff *skb)