linux-kernel - Re: [PATCH 2/2] Ensure num

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Date:   Fri, 1 Sep 2023 10:58:39 +0200
From:   Pablo Neira Ayuso <pablo@...filter.org>
To:     joao@...rdrivepizza.com
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 2/2] Ensure num_actions is not a negative

On Thu, Aug 31, 2023 at 06:04:37PM -0700, joao@...rdrivepizza.com wrote:
> From: Joao Moreira <joao.moreira@...el.com>
> 
> In nft_flow_rule_create function, num_actions is a signed integer. Yet,
> it is processed within a loop which increments its value. To prevent an
> overflow from occurring, check if num_actions is not only equal to 0,
> but also not negative.
> 
> After checking with maintainers, it was mentioned that front-end will
> cap the num_actions vlaue and that it is not possible to reach such
> condition for an overflow. Yet, for correctness, it is still better to
> fix this.
> 
> Signed-off-by: Joao Moreira <joao.moreira@...el.com>
> ---
>  net/netfilter/nf_tables_offload.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/netfilter/nf_tables_offload.c b/net/netfilter/nf_tables_offload.c
> index 12ab78fa5d84..20dbc95de895 100644
> --- a/net/netfilter/nf_tables_offload.c
> +++ b/net/netfilter/nf_tables_offload.c
> @@ -102,7 +102,7 @@ struct nft_flow_rule *nft_flow_rule_create(struct net *net,
>  		expr = nft_expr_next(expr);
>  	}
>  
> -	if (num_actions == 0)
> +	if (num_actions <= 0)
>  		return ERR_PTR(-EOPNOTSUPP);

Better turn num_actions into unsigned int I'd suggest.

Next hypothetical problem would be an overflow in the number of
actions, you could check for UINT_MAX if you like here to report
ENOMEM.

Thanks.

>  	flow = nft_flow_rule_alloc(num_actions);
> -- 
> 2.41.0
>