netdev - Re: [PATCH net v2 2/2] lwtunnel: Fix oops on state free after encap module unload

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Date:   Tue, 24 Jan 2017 16:26:21 +0000
From:   Robert Shearman <rshearma@...cade.com>
To:     David Miller <davem@...emloft.net>
CC:     <netdev@...r.kernel.org>, <tom@...bertland.com>,
        <roopa@...ulusnetworks.com>, <david.lebrun@...ouvain.be>,
        <tgraf@...g.ch>, <dsa@...ulusnetworks.com>
Subject: Re: [PATCH net v2 2/2] lwtunnel: Fix oops on state free after encap
 module unload

On 23/01/17 20:42, David Miller wrote:
> From: Robert Shearman <rshearma@...cade.com>
> Date: Sat, 21 Jan 2017 00:21:26 +0000
>
>> @@ -115,8 +115,12 @@ int lwtunnel_build_state(struct net_device *dev, u16 encap_type,
>>  	ret = -EOPNOTSUPP;
>>  	rcu_read_lock();
>
> Here 'ret' equals -EOPNOTSUPP
>
>>  	ops = rcu_dereference(lwtun_encaps[encap_type]);
>> -	if (likely(ops && ops->build_state))
>> -		ret = ops->build_state(dev, encap, family, cfg, lws);
>> +	if (likely(ops)) {
>> +		if (likely(try_module_get(ops->owner) && ops->build_state))
>> +			ret = ops->build_state(dev, encap, family, cfg, lws);
>> +		if (ret)
>> +			module_put(ops->owner);
>
> If try_module_get() fails, 'ret' will still be -EOPNOTSUPP and we will
> module_put() on a module we did not grab a reference to.
>
> I think you need to adjust the logic here.  You only want to 'put' if
> try_module_get() succeeds and ->build_state() returns an error.

Indeed, good point. Will address in a v3 shortly.

Thanks,
Rob