Patch "netem: fix skb_orphan_partial()" has been added to the 4.4-stable tree

[<gregkh@linuxfoundation.org>]

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

    netem: fix skb_orphan_partial()

to the 4.4-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:
     netem-fix-skb_orphan_partial.patch
and it can be found in the queue-4.4 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 f6ba8d33cfbb46df569972e64dbb5bb7e929bfd9 Mon Sep 17 00:00:00 2001
From: Eric Dumazet <edumazet@google.com>
Date: Thu, 11 May 2017 15:24:41 -0700
Subject: netem: fix skb_orphan_partial()

From: Eric Dumazet <edumazet@google.com>

commit f6ba8d33cfbb46df569972e64dbb5bb7e929bfd9 upstream.

I should have known that lowering skb->truesize was dangerous :/

In case packets are not leaving the host via a standard Ethernet device,
but looped back to local sockets, bad things can happen, as reported
by Michael Madsen ( https://bugzilla.kernel.org/show_bug.cgi?id=195713 )

So instead of tweaking skb->truesize, lets change skb->destructor
and keep a reference on the owner socket via its sk_refcnt.

Fixes: f2f872f9272a ("netem: Introduce skb_orphan_partial() helper")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Michael Madsen <mkm@nabto.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
 net/core/sock.c |   12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1690,17 +1690,17 @@ EXPORT_SYMBOL(skb_set_owner_w);
 
 void skb_orphan_partial(struct sk_buff *skb)
 {
-	/* TCP stack sets skb->ooo_okay based on sk_wmem_alloc,
-	 * so we do not completely orphan skb, but transfert all
-	 * accounted bytes but one, to avoid unexpected reorders.
-	 */
 	if (skb->destructor == sock_wfree
 #ifdef CONFIG_INET
 	    || skb->destructor == tcp_wfree
 #endif
 		) {
-		atomic_sub(skb->truesize - 1, &skb->sk->sk_wmem_alloc);
-		skb->truesize = 1;
+		struct sock *sk = skb->sk;
+
+		if (atomic_inc_not_zero(&sk->sk_refcnt)) {
+			atomic_sub(skb->truesize, &sk->sk_wmem_alloc);
+			skb->destructor = sock_efree;
+		}
 	} else {
 		skb_orphan(skb);
 	}


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

queue-4.4/sctp-do-not-inherit-ipv6_-mc-ac-fl-_list-from-parent.patch
queue-4.4/tcp-avoid-fastopen-api-to-be-used-on-af_unspec.patch
queue-4.4/tcp-eliminate-negative-reordering-in-tcp_clean_rtx_queue.patch
queue-4.4/netem-fix-skb_orphan_partial.patch
queue-4.4/dccp-tcp-do-not-inherit-mc_list-from-parent.patch
queue-4.4/tcp-avoid-fragmenting-peculiar-skbs-in-sack.patch
queue-4.4/ipv6-dccp-do-not-inherit-ipv6_mc_list-from-parent.patch
queue-4.4/ipv6-fix-out-of-bound-writes-in-__ip6_append_data.patch
queue-4.4/ipv4-add-reference-counting-to-metrics.patch