Patch "netfilter: ctnetlink: fix incorrect nf_ct_put during hash resize" has been added to the 4.9-stable tree

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

netfilter: ctnetlink: fix incorrect nf_ct_put during hash resize

to the 4.9-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:
netfilter-ctnetlink-fix-incorrect-nf_ct_put-during-hash-resize.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Liping Zhang <[email protected]>
Date: Sun, 21 May 2017 07:22:49 +0800
Subject: netfilter: ctnetlink: fix incorrect nf_ct_put during hash resize

From: Liping Zhang <[email protected]>

[ Upstream commit fefa92679dbe0c613e62b6c27235dcfbe9640ad1 ]

If nf_conntrack_htable_size was adjusted by the user during the ct dump operation, we may invoke nf_ct_put twice for the same ct, i.e. the "last" ct. This will cause the ct will be freed but still linked in hash buckets.

It's very easy to reproduce the problem by the following commands:

  # while : ; do
  echo $RANDOM > /proc/sys/net/netfilter/nf_conntrack_buckets
  done
  # while : ; do
  conntrack -L
  done
  # iperf -s 127.0.0.1 &
  # iperf -c 127.0.0.1 -P 60 -t 36000

After a while, the system will hang like this:
NMI watchdog: BUG: soft lockup - CPU#1 stuck for 22s! [bash:20184] NMI watchdog: BUG: soft lockup - CPU#0 stuck for 22s! [iperf:20382]
...

So at last if we find cb->args[1] is equal to "last", this means hash resize happened, then we can set cb->args[1] to 0 to fix the above issue.

---
 net/netfilter/nf_conntrack_netlink.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

@@ -890,8 +890,13 @@ restart:
 	}
 out:
 	local_bh_enable();
-	if (last)
+	if (last) {
+		/* nf ct hash resize happened, now clear the leftover. */
+		if ((struct nf_conn *)cb->args[1] == last)
+			cb->args[1] = 0;
+
 		nf_ct_put(last);
+	}
 
 	while (i) {
 		i--;

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/netfilter-ctnetlink-fix-incorrect-nf_ct_put-during-hash-resize.patch