[3.16.y-ckt stable] Patch "netlink: Don't reorder loads/stores before marking mmap netlink frame as available" has been added to staging queue

[Luis Henriques]

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

    netlink: Don't reorder loads/stores before marking mmap netlink frame as available

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?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt5.

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 e5048768a193913ccc17774ca58d333510497770 Mon Sep 17 00:00:00 2001
From: Thomas Graf <tgraf at suug.ch>
Date: Thu, 18 Dec 2014 10:30:26 +0000
Subject: netlink: Don't reorder loads/stores before marking mmap netlink frame
 as available

commit a18e6a186f53af06937a2c268c72443336f4ab56 upstream.

Each mmap Netlink frame contains a status field which indicates
whether the frame is unused, reserved, contains data or needs to
be skipped. Both loads and stores may not be reordeded and must
complete before the status field is changed and another CPU might
pick up the frame for use. Use an smp_mb() to cover needs of both
types of callers to netlink_set_status(), callers which have been
reading data frame from the frame, and callers which have been
filling or releasing and thus writing to the frame.

- Example code path requiring a smp_rmb():
  memcpy(skb->data, (void *)hdr + NL_MMAP_HDRLEN, hdr->nm_len);
  netlink_set_status(hdr, NL_MMAP_STATUS_UNUSED);

- Example code path requiring a smp_wmb():
  hdr->nm_uid	= from_kuid(sk_user_ns(sk), NETLINK_CB(skb).creds.uid);
  hdr->nm_gid	= from_kgid(sk_user_ns(sk), NETLINK_CB(skb).creds.gid);
  netlink_frame_flush_dcache(hdr);
  netlink_set_status(hdr, NL_MMAP_STATUS_VALID);

Fixes: f9c228 ("netlink: implement memory mapped recvmsg()")
Reported-by: Eric Dumazet <eric.dumazet at gmail.com>
Signed-off-by: Thomas Graf <tgraf at suug.ch>
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 | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 625593d866ac..256ce8b84456 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -535,9 +535,9 @@ static enum nl_mmap_status netlink_get_status(const struct nl_mmap_hdr *hdr)
 static void netlink_set_status(struct nl_mmap_hdr *hdr,
 			       enum nl_mmap_status status)
 {
+	smp_mb();
 	hdr->nm_status = status;
 	flush_dcache_page(pgvec_to_page(hdr));
-	smp_wmb();
 }

 static struct nl_mmap_hdr *
--
2.1.4