[3.16.y-ckt stable] Patch "netlink: not trim skb for mmaped socket when dump" has been added to the 3.16.y-ckt tree

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    netlink: not trim skb for mmaped socket when dump

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-ckt25.

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

---8<------------------------------------------------------------

>From c501d329b2d8052184cd63b2b7e86088f2f33187 Mon Sep 17 00:00:00 2001
From: Ken-ichirou MATSUZAWA <chamaken at gmail.com>
Date: Fri, 29 Jan 2016 10:45:50 +0900
Subject: netlink: not trim skb for mmaped socket when dump

commit aa3a022094fac7f6e48050e139fa8a5a2e3265ce upstream.

We should not trim skb for mmaped socket since its buf size is fixed
and userspace will read as frame which data equals head. mmaped
socket will not call recvmsg, means max_recvmsg_len is 0,
skb_reserve was not called before commit: db65a3aaf29e.

Fixes: db65a3aaf29e (netlink: Trim skb to alloc size to avoid MSG_TRUNC)
Signed-off-by: Ken-ichirou MATSUZAWA <chamas at h4.dion.ne.jp>
Signed-off-by: David S. Miller <davem at davemloft.net>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 net/netlink/af_netlink.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 7e1ac5b5de0a..46cac8e31a16 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -2740,7 +2740,8 @@ static int netlink_dump(struct sock *sk)
 	 * reasonable static buffer based on the expected largest dump of a
 	 * single netdev. The outcome is MSG_TRUNC error.
 	 */
-	skb_reserve(skb, skb_tailroom(skb) - alloc_size);
+	if (!netlink_rx_is_mmaped(sk))
+		skb_reserve(skb, skb_tailroom(skb) - alloc_size);
 	netlink_skb_set_owner_r(skb, sk);

 	len = cb->dump(skb, cb);