Commit c7c49b8f authored Sep 29, 2015 by Eric Dumazet Committed by David S. Miller Oct 17, 2015

net: add pfmemalloc check in sk_add_backlog()



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: b4b9e355 ("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>

parent 5f715c09

include/net/sock.h

+8 −0

Original line number	Diff line number	Diff line
		@@ -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;

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