[PATCH nf v3 1/1] netfilter: snmp: Fix one possible panic when snmp_trap_helper fail to register

From: Gao Feng <redacted>

In the commit 93557f53e1fb ("netfilter: nf_conntrack: nf_conntrack snmp
helper"), the snmp_helper is replaced by nf_nat_snmp_hook. So the
snmp_helper is never registered. But it still tries to unregister the
snmp_helper, it could cause the panic.

Now remove the useless snmp_helper and the unregister call in the
error handler.

Fixes: 93557f53e1fb ("netfilter: nf_conntrack: nf_conntrack snmp helper")

Signed-off-by: Gao Feng <redacted>
---
 v3: Remove the angle brackets in description, per Sergei
 v2: Add the SHA1 ID in the description, per Sergei
 v1: Initial version

 net/ipv4/netfilter/nf_nat_snmp_basic.c | 14 +-------------
 1 file changed, 1 insertion(+), 13 deletions(-)

diff --git a/net/ipv4/netfilter/nf_nat_snmp_basic.c b/net/ipv4/netfilter/nf_nat_snmp_basic.c
index c9b52c3..5787364 100644
--- a/net/ipv4/netfilter/nf_nat_snmp_basic.c
+++ b/net/ipv4/netfilter/nf_nat_snmp_basic.c

@@ -1260,16 +1260,6 @@ static int help(struct sk_buff *skb, unsigned int protoff,
 	.timeout	= 180,
 };
 
-static struct nf_conntrack_helper snmp_helper __read_mostly = {
-	.me			= THIS_MODULE,
-	.help			= help,
-	.expect_policy		= &snmp_exp_policy,
-	.name			= "snmp",
-	.tuple.src.l3num	= AF_INET,
-	.tuple.src.u.udp.port	= cpu_to_be16(SNMP_PORT),
-	.tuple.dst.protonum	= IPPROTO_UDP,
-};
-
 static struct nf_conntrack_helper snmp_trap_helper __read_mostly = {
 	.me			= THIS_MODULE,
 	.help			= help,

@@ -1294,10 +1284,8 @@ static int __init nf_nat_snmp_basic_init(void)
 	RCU_INIT_POINTER(nf_nat_snmp_hook, help);
 
 	ret = nf_conntrack_helper_register(&snmp_trap_helper);
-	if (ret < 0) {
-		nf_conntrack_helper_unregister(&snmp_helper);
+	if (ret < 0)
 		return ret;
-	}
 	return ret;
 }
 

-- 
1.9.1

On Tue, Mar 21, 2017 at 08:22:29AM +0800, fgao@ikuai8.com wrote:

From: Gao Feng <redacted>

In the commit 93557f53e1fb ("netfilter: nf_conntrack: nf_conntrack snmp
helper"), the snmp_helper is replaced by nf_nat_snmp_hook. So the
snmp_helper is never registered. But it still tries to unregister the
snmp_helper, it could cause the panic.

This patch looks correct to me.

But probably for some reason I don't manage to trigger, how do you
reproduce this?

On Fri, Mar 24, 2017 at 01:21:30PM +0100, Pablo Neira Ayuso wrote:

On Tue, Mar 21, 2017 at 08:22:29AM +0800, fgao@ikuai8.com wrote:

quoted

From: Gao Feng <redacted>

In the commit 93557f53e1fb ("netfilter: nf_conntrack: nf_conntrack snmp
helper"), the snmp_helper is replaced by nf_nat_snmp_hook. So the
snmp_helper is never registered. But it still tries to unregister the
snmp_helper, it could cause the panic.

This patch looks correct to me.

But probably for some reason I don't manage to trigger, how do you
reproduce this?

I'm refering to the panic.

Hi Pablo,

-----Original Message-----
From: netfilter-devel-owner@vger.kernel.org
[mailto:netfilter-devel-owner@vger.kernel.org] On Behalf Of Pablo Neira

Ayuso

Sent: Friday, March 24, 2017 8:23 PM
To: fgao@ikuai8.com
Cc: davem@davemloft.net; jolsa@redhat.com;

netfilter-devel@vger.kernel.org;

netdev@vger.kernel.org; gfree.wind@gmail.com
Subject: Re: [PATCH nf v3 1/1] netfilter: snmp: Fix one possible panic

when

snmp_trap_helper fail to register

On Fri, Mar 24, 2017 at 01:21:30PM +0100, Pablo Neira Ayuso wrote:

quoted

On Tue, Mar 21, 2017 at 08:22:29AM +0800, fgao@ikuai8.com wrote:

quoted

From: Gao Feng <redacted>

In the commit 93557f53e1fb ("netfilter: nf_conntrack: nf_conntrack
snmp helper"), the snmp_helper is replaced by nf_nat_snmp_hook. So
the snmp_helper is never registered. But it still tries to
unregister the snmp_helper, it could cause the panic.

This patch looks correct to me.

But probably for some reason I don't manage to trigger, how do you
reproduce this?

I'm refering to the panic.

[高峰] 
It is got by reviewing the codes.
When nf_conntrack_helper_unregister(&snmp_helper), but snmp_helper didn't
register actually.
And snmp_helper. hnode is not initialized, it would trigger the issue when
hlist_del_rcu in nf_conntrack_helper_unregister.

Best Regards
Feng

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On Tue, Mar 21, 2017 at 08:22:29AM +0800, fgao@ikuai8.com wrote:

You can provide a more simplified version after this is removed, I
think:

@@ -1283,10 +1283,7 @@ static int __init nf_nat_snmp_basic_init(void)
        BUG_ON(nf_nat_snmp_hook != NULL);
        RCU_INIT_POINTER(nf_nat_snmp_hook, help);
 
-       ret = nf_conntrack_helper_register(&snmp_trap_helper);
-       if (ret < 0)
-               return ret;
-       return ret;
+       return nf_conntrack_helper_register(&snmp_trap_helper);
 }

-----Original Message-----
From: Pablo Neira Ayuso [mailto:pablo@netfilter.org]
Sent: Saturday, March 25, 2017 3:02 AM
To: fgao@ikuai8.com
Cc: davem@davemloft.net; jolsa@redhat.com;

netfilter-devel@vger.kernel.org;

netdev@vger.kernel.org; gfree.wind@gmail.com
Subject: Re: [PATCH nf v3 1/1] netfilter: snmp: Fix one possible panic

when

snmp_trap_helper fail to register

On Tue, Mar 21, 2017 at 08:22:29AM +0800, fgao@ikuai8.com wrote:

quoted

From: Gao Feng <redacted>

In the commit 93557f53e1fb ("netfilter: nf_conntrack: nf_conntrack
snmp helper"), the snmp_helper is replaced by nf_nat_snmp_hook. So the
snmp_helper is never registered. But it still tries to unregister the
snmp_helper, it could cause the panic.

Now remove the useless snmp_helper and the unregister call in the
error handler.

Fixes: 93557f53e1fb ("netfilter: nf_conntrack: nf_conntrack snmp
helper")

Signed-off-by: Gao Feng <redacted>
---
 v3: Remove the angle brackets in description, per Sergei
 v2: Add the SHA1 ID in the description, per Sergei
 v1: Initial version

 net/ipv4/netfilter/nf_nat_snmp_basic.c | 14 +-------------
 1 file changed, 1 insertion(+), 13 deletions(-)

diff --git a/net/ipv4/netfilter/nf_nat_snmp_basic.c

b/net/ipv4/netfilter/nf_nat_snmp_basic.c
index c9b52c3..5787364 100644

--- a/net/ipv4/netfilter/nf_nat_snmp_basic.c
+++ b/net/ipv4/netfilter/nf_nat_snmp_basic.c

@@ -1260,16 +1260,6 @@ static int help(struct sk_buff *skb, unsigned int

protoff,

quoted

 	.timeout	= 180,
 };

-static struct nf_conntrack_helper snmp_helper __read_mostly = {
-	.me			= THIS_MODULE,
-	.help			= help,
-	.expect_policy		= &snmp_exp_policy,
-	.name			= "snmp",
-	.tuple.src.l3num	= AF_INET,
-	.tuple.src.u.udp.port	= cpu_to_be16(SNMP_PORT),
-	.tuple.dst.protonum	= IPPROTO_UDP,
-};
-
 static struct nf_conntrack_helper snmp_trap_helper __read_mostly = {
 	.me			= THIS_MODULE,
 	.help			= help,

@@ -1294,10 +1284,8 @@ static int __init nf_nat_snmp_basic_init(void)
 	RCU_INIT_POINTER(nf_nat_snmp_hook, help);

 	ret = nf_conntrack_helper_register(&snmp_trap_helper);
-	if (ret < 0) {
-		nf_conntrack_helper_unregister(&snmp_helper);
+	if (ret < 0)
 		return ret;
-	}
 	return ret;

You can provide a more simplified version after this is removed, I
think:

Ok. I thought it should not change the style for bug fix.
I would sent the update patch.

Best Regards
Feng