net: sk_clone_lock() should only do get_net() if the parent is not a kernel socket

The newsk returned by sk_clone_lock should hold a get_net() reference if, and only if, the parent is not a kernel socket (making this similar to sk_alloc()).

E.g,. for the SYN_RECV path, tcp_v4_syn_recv_sock->..inet_csk_clone_lock sets up the syn_recv newsk from sk_clone_lock. When the parent (listen) socket is a kernel socket (defined in sk_alloc() as having sk_net_refcnt == 0), then the newsk should also have a 0 sk_net_refcnt and should not hold a get_net() reference.

netns of kernel sockets.")

---
v2: pulled patch #3 out of the RFC patch-set for RDS-TCP netns fixes;
Added Fixes, Acked-by, Cc fields based on mailing list feedback from Eric Dumazet.

 net/core/sock.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

index 08f16db..371d1b7 100644
@@ -1497,7 +1497,8 @@ struct sock *sk_clone_lock(const struct sock *sk, const gfp_t priority)
 		sock_copy(newsk, sk);
 
 		/* SANITY */
-		get_net(sock_net(newsk));
+		if (likely(newsk->sk_net_refcnt))
+			get_net(sock_net(newsk));
 		sk_node_init(&newsk->sk_node);
 		sock_lock_init(newsk);
 		bh_lock_sock(newsk);

1.7.1

From: Sowmini Varadhan <[email protected]>
Date: Thu, 30 Jul 2015 15:50:36 +0200

Applied, thanks everyone.