lkml.org 
[lkml]   [2019]   [Dec]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH AUTOSEL 4.9 03/38] netfilter: ctnetlink: netns exit must wait for callbacks
Date
From: Florian Westphal <fw@strlen.de>

[ Upstream commit 18a110b022a5c02e7dc9f6109d0bd93e58ac6ebb ]

Curtis Taylor and Jon Maxwell reported and debugged a crash on 3.10
based kernel.

Crash occurs in ctnetlink_conntrack_events because net->nfnl socket is
NULL. The nfnl socket was set to NULL by netns destruction running on
another cpu.

The exiting network namespace calls the relevant destructors in the
following order:

1. ctnetlink_net_exit_batch

This nulls out the event callback pointer in struct netns.

2. nfnetlink_net_exit_batch

This nulls net->nfnl socket and frees it.

3. nf_conntrack_cleanup_net_list

This removes all remaining conntrack entries.

This is order is correct. The only explanation for the crash so ar is:

cpu1: conntrack is dying, eviction occurs:
-> nf_ct_delete()
-> nf_conntrack_event_report \
-> nf_conntrack_eventmask_report
-> notify->fcn() (== ctnetlink_conntrack_events).

cpu1: a. fetches rcu protected pointer to obtain ctnetlink event callback.
b. gets interrupted.
cpu2: runs netns exit handlers:
a runs ctnetlink destructor, event cb pointer set to NULL.
b runs nfnetlink destructor, nfnl socket is closed and set to NULL.
cpu1: c. resumes and trips over NULL net->nfnl.

Problem appears to be that ctnetlink_net_exit_batch only prevents future
callers of nf_conntrack_eventmask_report() from obtaining the callback.
It doesn't wait of other cpus that might have already obtained the
callbacks address.

I don't see anything in upstream kernels that would prevent similar
crash: We need to wait for all cpus to have exited the event callback.

Fixes: 9592a5c01e79dbc59eb56fa ("netfilter: ctnetlink: netns support")
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/netfilter/nf_conntrack_netlink.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/net/netfilter/nf_conntrack_netlink.c b/net/netfilter/nf_conntrack_netlink.c
index deea281ab169..5e28702c801f 100644
--- a/net/netfilter/nf_conntrack_netlink.c
+++ b/net/netfilter/nf_conntrack_netlink.c
@@ -3388,6 +3388,9 @@ static void __net_exit ctnetlink_net_exit_batch(struct list_head *net_exit_list)

list_for_each_entry(net, net_exit_list, exit_list)
ctnetlink_net_exit(net);
+
+ /* wait for other cpus until they are done with ctnl_notifiers */
+ synchronize_rcu();
}

static struct pernet_operations ctnetlink_net_ops = {
--
2.20.1
\
 
 \ /
  Last update: 2019-12-27 19:20    [W:0.105 / U:0.924 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site