@@ -1988,12 +1988,19 @@ void udp_v4_early_demux(struct sk_buff *skb)
skb->sk = sk;
skb->destructor = sock_edemux;
- dst = sk->sk_rx_dst;
+ dst = ACCESS_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)
This is a note to let you know that I have just added a patch titled udp: fix dst races with multicast early demux to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree which can be found at: http://kernel.ubuntu.com/git/ubuntu/linux.git/log/?h=linux-3.16.y-queue This patch is scheduled to be released in version 3.16.7-ckt17. If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.16.y-ckt tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Luis ------ From fd6a8a150559a8f643990b1b9eca8eb266407369 Mon Sep 17 00:00:00 2001 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 commit 10e2eb878f3ca07ac2f05fa5ca5e6c4c9174a27a upstream. 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> [ luis: backported to 3.16: used davem's backport to 3.14 ] Signed-off-by: Luis Henriques <luis.henriques@canonical.com> --- net/ipv4/udp.c | 13 ++++++++++--- 1 file changed, 10 insertions(+), 3 deletions(-)