Subject: Re: [PATCH v3 1/2] Make loop indexes unsigned

From: Pablo Neira Ayuso <[email-masked]>
Date: Thu, 28 Sep 2023 15:40:13 +0200

On Wed, Sep 27, 2023 at 09:47:14AM -0700, [email-masked] wrote:
> From: Joao Moreira <[email-masked]>
> 
> 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 <[email-masked]>
> ---
>  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.

>  
>  	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
>