Patch "net: add pfmemalloc check in sk_add_backlog()" has been added to the 4.2-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    net: add pfmemalloc check in sk_add_backlog()

to the 4.2-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     net-add-pfmemalloc-check-in-sk_add_backlog.patch
and it can be found in the queue-4.2 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


>From foo@baz Thu Oct 22 17:25:24 PDT 2015
From: Eric Dumazet <edumazet@google.com>
Date: Tue, 29 Sep 2015 18:52:25 -0700
Subject: net: add pfmemalloc check in sk_add_backlog()

From: Eric Dumazet <edumazet@google.com>

[ 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>
---
 include/net/sock.h |    8 ++++++++
 1 file changed, 8 insertions(+)

--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -826,6 +826,14 @@ static inline __must_check int sk_add_ba
 	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;


Patches currently in stable-queue which might be from edumazet@google.com are

queue-4.2/inet-fix-races-in-reqsk_queue_hash_req.patch
queue-4.2/net-add-pfmemalloc-check-in-sk_add_backlog.patch
queue-4.2/inet-fix-race-in-reqsk_queue_unlink.patch
queue-4.2/net-unix-fix-logic-about-sk_peek_offset.patch
queue-4.2/act_mirred-clear-sender-cpu-before-sending-to-tx.patch