Patch "udp: fix dst races with multicast early demux" has been added to the 4.1-stable tree

[<gregkh@linuxfoundation.org>]

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

    udp: fix dst races with multicast early demux

to the 4.1-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:
     udp-fix-dst-races-with-multicast-early-demux.patch
and it can be found in the queue-4.1 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 Sat Sep 26 11:13:07 PDT 2015
From: Eric Dumazet <edumazet@google.com>
Date: Sat, 1 Aug 2015 12:14:33 +0200
Subject: udp: fix dst races with multicast early demux
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 10e2eb878f3ca07ac2f05fa5ca5e6c4c9174a27a ]

Multicast dst are not cached. They carry DST_NOCACHE.

As mentioned in commit f8864972126899 ("ipv4: fix dst race in
sk_dst_get()"), these dst need special care before caching them
into a socket.

Caching them is allowed only if their refcnt was not 0, ie we
must use atomic_inc_not_zero()

Also, we must use READ_ONCE() to fetch sk->sk_rx_dst, as mentioned
in commit d0c294c53a771 ("tcp: prevent fetching dst twice in early demux
code")

Fixes: 421b3885bf6d ("udp: ipv4: Add udp early demux")
Tested-by: Gregory Hoggarth <Gregory.Hoggarth@alliedtelesis.co.nz>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Gregory Hoggarth <Gregory.Hoggarth@alliedtelesis.co.nz>
Reported-by: Alex Gartrell <agartrell@fb.com>
Cc: Michal Kubeček <mkubecek@suse.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/ipv4/udp.c |   13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1995,12 +1995,19 @@ void udp_v4_early_demux(struct sk_buff *
 
 	skb->sk = sk;
 	skb->destructor = sock_efree;
-	dst = sk->sk_rx_dst;
+	dst = READ_ONCE(sk->sk_rx_dst);
 
 	if (dst)
 		dst = dst_check(dst, 0);
-	if (dst)
-		skb_dst_set_noref(skb, dst);
+	if (dst) {
+		/* DST_NOCACHE can not be used without taking a reference */
+		if (dst->flags & DST_NOCACHE) {
+			if (likely(atomic_inc_not_zero(&dst->__refcnt)))
+				skb_dst_set(skb, dst);
+		} else {
+			skb_dst_set_noref(skb, dst);
+		}
+	}
 }
 
 int udp_rcv(struct sk_buff *skb)


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

queue-4.1/udp-fix-dst-races-with-multicast-early-demux.patch
queue-4.1/fq_codel-fix-a-use-after-free.patch
queue-4.1/inet-fix-possible-request-socket-leak.patch
queue-4.1/ipv6-lock-socket-in-ip6_datagram_connect.patch
queue-4.1/net-fix-skb-csum-races-when-peeking.patch
queue-4.1/inet-fix-races-with-reqsk-timers.patch
queue-4.1/net-graceful-exit-from-netif_alloc_netdev_queues.patch
queue-4.1/bridge-fix-potential-crash-in-__netdev_pick_tx.patch
queue-4.1/inet-frags-fix-defragmented-packet-s-ip-header-for-af_packet.patch