[PATCH 3.2 047/106] netfilter: ctnetlink: fix incorrect nf_ct_put during hash resize

From: Ben Hutchings
Date: Sat Sep 09 2017 - 18:44:33 EST

3.2.93-rc1 review patch. If anyone has any objections, please let me know.


From: Liping Zhang <zlpnobody@xxxxxxxxx>

commit fefa92679dbe0c613e62b6c27235dcfbe9640ad1 upstream.

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
# while : ; do
conntrack -L
# iperf -s &
# iperf -c -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

Fixes: d205dc40798d ("[NETFILTER]: ctnetlink: fix deadlock in table dumping")
Signed-off-by: Liping Zhang <zlpnobody@xxxxxxxxx>
Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
[bwh: Backported to 3.2: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
net/netfilter/nf_conntrack_netlink.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

--- a/net/netfilter/nf_conntrack_netlink.c
+++ b/net/netfilter/nf_conntrack_netlink.c
@@ -731,8 +731,13 @@ restart:
- 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;
+ }

return skb->len;