2023-09-01 07:01:49

by Joao Moreira

Subject: [PATCH 2/2] Ensure num_actions is not a negative

From: Joao Moreira <[email protected]>

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 <[email protected]>
---
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);

flow = nft_flow_rule_alloc(num_actions);
--
2.41.0

2023-09-01 14:28:41

by Pablo Neira Ayuso

Subject: Re: [PATCH 2/2] Ensure num_actions is not a negative

On Thu, Aug 31, 2023 at 06:04:37PM -0700, [email protected] wrote:
> From: Joao Moreira <[email protected]>
>
> 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 <[email protected]>
> ---
> 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
>