net: add pfmemalloc check in sk_add_backlog()

[ Upstream commit c7c49b8fde26b74277188bdc6c9dca38db6fa35b ]

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: b4b9e35585089 ("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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/include/net/sock.h b/include/net/sock.h
index c0aad07160ef3e3b03be628634ca6ab70aec339c..95dc0c8a9dac078d640bec98170b8eb81b8d7cc5 100644 (file)
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -782,6 +782,14 @@ static inline __must_check int sk_add_backlog(struct sock *sk, struct sk_buff *s
        if (sk_rcvqueues_full(sk, skb, 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;