Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::3:6 as permitted sender) client-ip=2620:137:e000::3:6;
MIME-Version: 1.0
Date:   Thu, 28 Sep 2023 19:53:14 -0700
From:   Joao Moreira <joao@overdrivepizza.com>
To:     Pablo Neira Ayuso <pablo@netfilter.org>
Cc:     netfilter-devel@vger.kernel.org, coreteam@netfilter.org,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        kadlec@netfilter.org, fw@strlen.de, davem@davemloft.net,
        edumazet@google.com, kuba@kernel.org, pabeni@redhat.com,
        rkannoth@marvell.com, wojciech.drewek@intel.com,
        steen.hegenlund@microhip.com, keescook@chromium.org,
        Joao Moreira <joao.moreira@intel.com>
Subject: Re: [PATCH v3 1/2] Make loop indexes unsigned
In-Reply-To: <ZRWCPTVd7b6+a7N5@calendula>
References: <20230927164715.76744-1-joao@overdrivepizza.com>
 <20230927164715.76744-2-joao@overdrivepizza.com>
 <ZRWCPTVd7b6+a7N5@calendula>
Message-ID: <77df92a5627411471f1f374d41ae500c@overdrivepizza.com>
Content-Type: text/plain; charset=US-ASCII;
 format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 2023-09-28 06:40, Pablo Neira Ayuso wrote:
> On Wed, Sep 27, 2023 at 09:47:14AM -0700, joao@overdrivepizza.com 
> wrote:
>> From: Joao Moreira <joao.moreira@intel.com>
>> 
>> Both flow_rule_alloc and offload_action_alloc functions received an
>> unsigned num_actions parameters which are then operated within a loop.
>> The index of this loop is declared as a signed int. If it was possible
>> to pass a large enough num_actions to these functions, it would lead 
>> to
>> an out of bounds write.
>> 
>> After checking with maintainers, it was mentioned that front-end will
>> cap the num_actions value and that it is not possible to reach this
>> function with such a large number. Yet, for correctness, it is still
>> better to fix this.
>> 
>> This issue was observed by the commit author while reviewing a 
>> write-up
>> regarding a CVE within the same subsystem [1].
>> 
>> 1 - https://nickgregory.me/post/2022/03/12/cve-2022-25636/
>> 
>> Signed-off-by: Joao Moreira <joao.moreira@intel.com>
>> ---
>>  net/core/flow_offload.c | 4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>> 
>> diff --git a/net/core/flow_offload.c b/net/core/flow_offload.c
>> index bc5169482710..bc3f53a09d8f 100644
>> --- a/net/core/flow_offload.c
>> +++ b/net/core/flow_offload.c
>> @@ -10,7 +10,7 @@
>>  struct flow_rule *flow_rule_alloc(unsigned int num_actions)
>>  {
>>  	struct flow_rule *rule;
>> -	int i;
>> +	unsigned int i;
> 
> With the 2^8 cap, I don't think this patch is required anymore.

Hm. While I understand that there is not a significant menace haunting 
this... would it be good for (1) type correctness and (2) prevent that 
things blow up if something changes and someone misses this spot?

> 
>> 
>>  	rule = kzalloc(struct_size(rule, action.entries, num_actions),
>>  		       GFP_KERNEL);
>> @@ -31,7 +31,7 @@ EXPORT_SYMBOL(flow_rule_alloc);
>>  struct flow_offload_action *offload_action_alloc(unsigned int 
>> num_actions)
>>  {
>>  	struct flow_offload_action *fl_action;
>> -	int i;
>> +	unsigned int i;
>> 
>>  	fl_action = kzalloc(struct_size(fl_action, action.entries, 
>> num_actions),
>>  			    GFP_KERNEL);
>> --
>> 2.42.0
>>