[PATCH 1/1] netfilter: Fix kernel panic in nfulnl_rcv_nl_event

[PATCH 1/1] netfilter: Fix kernel panic in nfulnl_rcv_nl_event

[Francesco Ruggeri]

nfnetlink_log_init registers netlink callback nfulnl_rcv_nl_event before
registering the pernet_subsys, but the callback relies on data structures
allocated by pernet init functions.
When nfnetlink_log is loaded, if a netlink message is received after
the netlink callback is registered but before the pernet_subsys is
registered, the kernel will panic in the sequence

nfulnl_rcv_nl_event
  nfnl_log_pernet
    net_generic
      BUG_ON(id == 0)  where id is nfnl_log_net_id.

The panic can be easily reproduced in 4.0.3 by:

while true ;do modprobe nfnetlink_log ; rmmod nfnetlink_log ; done &
while true ;do ip netns add dummy ; ip netns del dummy ; done &

This patch moves register_pernet_subsys to earlier in nfnetlink_log_init.

Notice that the BUG_ON hit in 4.0.3 was recently removed in 2591ffd308
["netns: remove BUG_ONs from net_generic()"].

Signed-off-by: Francesco Ruggeri <fruggeri@arista.com>
---
 net/netfilter/nfnetlink_log.c | 17 +++++++++--------
 1 file changed, 9 insertions(+), 8 deletions(-)

diff --git a/net/netfilter/nfnetlink_log.c b/net/netfilter/nfnetlink_log.c
index 3ad9126..536ced5 100644
--- a/net/netfilter/nfnetlink_log.c
+++ b/net/netfilter/nfnetlink_log.c
@@ -1075,6 +1075,12 @@ static int __init nfnetlink_log_init(void)
 {
 	int status = -ENOMEM;
 
+	status = register_pernet_subsys(&nfnl_log_net_ops);
+	if (status < 0) {
+		pr_err("failed to register pernet ops\n");
+		goto out;
+	}
+
 	netlink_register_notifier(&nfulnl_rtnl_notifier);
 	status = nfnetlink_subsys_register(&nfulnl_subsys);
 	if (status < 0) {
@@ -1088,28 +1094,23 @@ static int __init nfnetlink_log_init(void)
 		goto cleanup_subsys;
 	}
 
-	status = register_pernet_subsys(&nfnl_log_net_ops);
-	if (status < 0) {
-		pr_err("failed to register pernet ops\n");
-		goto cleanup_logger;
-	}
 	return status;
 
-cleanup_logger:
-	nf_log_unregister(&nfulnl_logger);
 cleanup_subsys:
 	nfnetlink_subsys_unregister(&nfulnl_subsys);
 cleanup_netlink_notifier:
 	netlink_unregister_notifier(&nfulnl_rtnl_notifier);
+	unregister_pernet_subsys(&nfnl_log_net_ops);
+out:
 	return status;
 }
 
 static void __exit nfnetlink_log_fini(void)
 {
-	unregister_pernet_subsys(&nfnl_log_net_ops);
 	nf_log_unregister(&nfulnl_logger);
 	nfnetlink_subsys_unregister(&nfulnl_subsys);
 	netlink_unregister_notifier(&nfulnl_rtnl_notifier);
+	unregister_pernet_subsys(&nfnl_log_net_ops);
 }
 
 MODULE_DESCRIPTION("netfilter userspace logging");
-- 
1.8.1.4

Re: [PATCH 1/1] netfilter: Fix kernel panic in nfulnl_rcv_nl_event

[Pablo Neira Ayuso]

On Sun, May 17, 2015 at 02:30:31PM -0700, Francesco Ruggeri wrote:
> nfnetlink_log_init registers netlink callback nfulnl_rcv_nl_event before
> registering the pernet_subsys, but the callback relies on data structures
> allocated by pernet init functions.
> When nfnetlink_log is loaded, if a netlink message is received after
> the netlink callback is registered but before the pernet_subsys is
> registered, the kernel will panic in the sequence
> 
> nfulnl_rcv_nl_event
>   nfnl_log_pernet
>     net_generic
>       BUG_ON(id == 0)  where id is nfnl_log_net_id.
> 
> The panic can be easily reproduced in 4.0.3 by:
> 
> while true ;do modprobe nfnetlink_log ; rmmod nfnetlink_log ; done &
> while true ;do ip netns add dummy ; ip netns del dummy ; done &
> 
> This patch moves register_pernet_subsys to earlier in nfnetlink_log_init.
> 
> Notice that the BUG_ON hit in 4.0.3 was recently removed in 2591ffd308
> ["netns: remove BUG_ONs from net_generic()"].

I'm going to send a v2 of this patch with two changes:

* We have the same problem in nfnetlink_queue.
* Remove status = -ENOMEM as it is scratched soon thereafter.

Please, have a look at the patch I'll send after this and confirm this
looks good to you.