linux-kernel - Re: [PATCH v3 1/2] Make loop indexes unsigned

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Date:   Thu, 28 Sep 2023 19:53:14 -0700
From:   Joao Moreira <joao@...rdrivepizza.com>
To:     Pablo Neira Ayuso <pablo@...filter.org>
Cc:     netfilter-devel@...r.kernel.org, coreteam@...filter.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        kadlec@...filter.org, fw@...len.de, davem@...emloft.net,
        edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
        rkannoth@...vell.com, wojciech.drewek@...el.com,
        steen.hegenlund@...rohip.com, keescook@...omium.org,
        Joao Moreira <joao.moreira@...el.com>
Subject: Re: [PATCH v3 1/2] Make loop indexes unsigned

On 2023-09-28 06:40, Pablo Neira Ayuso wrote:
> On Wed, Sep 27, 2023 at 09:47:14AM -0700, joao@...rdrivepizza.com 
> wrote:
>> From: Joao Moreira <joao.moreira@...el.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@...el.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
>>