[PATCH 3.12 087/123] net: add pfmemalloc check in sk_add_backlog()

From: Jiri Slaby
Date: Wed Oct 28 2015 - 10:11:42 EST

From: Eric Dumazet <edumazet@xxxxxxxxxx>

3.12-stable review patch. If anyone has any objections, please let me know.


[ 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@xxxxxxxxxx>
Reported-by: Greg Thelen <gthelen@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
include/net/sock.h | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/include/net/sock.h b/include/net/sock.h
index d157f4f56f01..4f355e69e5d2 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -788,6 +788,14 @@ 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;

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