net: clear sk_err_soft in sk_clone_lock()

commit e551c32d upstream.

At accept() time, it is possible the parent has a non zero
sk_err_soft, leftover from a prior error.

Make sure we do not leave this value in the child, as it
makes future getsockopt(SO_ERROR) calls quite unreliable.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Willy Tarreau <w@1wt.eu>

net/core/sock.c

@@ -1515,6 +1515,7 @@ struct sock *sk_clone_lock(const struct sock *sk, const gfp_t priority)
 		}
 
 		newsk->sk_err	   = 0;
+		newsk->sk_err_soft = 0;
 		newsk->sk_priority = 0;
 		/*
 		 * Before updating sk_refcnt, we must commit prior changes to memory