net: add pfmemalloc check in sk_add_backlog()

edumazet · davem330 · commit c7c49b8fde26 · 2015-10-17T05:01:11.000-07:00
Greg reported crashes hitting the following check in __sk_backlog_rcv() BUG_ON(!sock_flag(sk, SOCK_MEMALLOC)); The pfmemalloc bit is currently checked in sk_filter(). This works correctly for TCP, because sk_filter() is ran in tcp_v[46]_rcv() before hitting the prequeue or backlog checks. For UDP or other protocols, this does not work, because the sk_filter() is ran from sock_queue_rcv_skb(), which might be called _after_ backlog queuing if socket is owned by user by the time packet is processed by softirq handler. Fixes: b4b9e35 ("netvm: set PF_MEMALLOC as appropriate during SKB processing") Signed-off-by: Eric Dumazet <edumazet@google.com> Reported-by: Greg Thelen <gthelen@google.com> Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/sock.h b/include/net/sock.h
@@ -828,6 +828,14 @@ static inline __must_check int sk_add_backlog(struct sock *sk, struct sk_buff *s
 	if (sk_rcvqueues_full(sk, limit))
 		return -ENOBUFS;
 
+	/*
+	 * If the skb was allocated from pfmemalloc reserves, only
+	 * allow SOCK_MEMALLOC sockets to use it as this socket is
+	 * helping free memory
+	 */
+	if (skb_pfmemalloc(skb) && !sock_flag(sk, SOCK_MEMALLOC))
+		return -ENOMEM;
+
 	__sk_add_backlog(sk, skb);
 	sk->sk_backlog.len += skb->truesize;
 	return 0;
