[NETLINK]: Fix race with recvmsg().

This bug causes:

assertion (!atomic_read(&sk->sk_rmem_alloc)) failed at net/netlink/af_netlink.c (122)

What's happening is that:

1) The skb is sent to socket 1.
2) Someone does a recvmsg on socket 1 and drops the ref on the skb.
   Note that the rmalloc is not returned at this point since the
   skb is still referenced.
3) The same skb is now sent to socket 2.

This version of the fix resurrects the skb_orphan call that was moved
out, last time we had 'shared-skb troubles'. It is practically a no-op
in the common case, but still prevents the possible race with recvmsg.

Signed-off-by: Tommy S. Christensen <tommy.christensen@tpack.net>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 733bf52cef3e72c663a9f4bc7f90cecab421c706..b40c9a976969e287f26c83ccd00485ff0744a9ad 100644 (file)
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -697,6 +697,7 @@ static __inline__ int netlink_broadcast_deliver(struct sock *sk, struct sk_buff
 
        if (atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf &&
            !test_bit(0, &nlk->state)) {
+               skb_orphan(skb);
                skb_set_owner_r(skb, sk);
                skb_queue_tail(&sk->sk_receive_queue, skb);
                sk->sk_data_ready(sk, skb->len);