diff mbox series

[v2,2/2] Make num_actions unsigned

Message ID 20230927020221.85292-3-joao@overdrivepizza.com
State New
Headers
Series Prevent potential write out of bounds |

Commit Message

Joao Moreira Sept. 27, 2023, 2:02 a.m. UTC 
  From: Joao Moreira <joao.moreira@intel.com>

Currently, 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, make it unsigned and
also check if it reaches UINT_MAX when being incremented.

After checking with maintainers, it was mentioned that front-end will
cap the num_actions value and that it is not possible to reach such
condition for an overflow. 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/netfilter/nf_tables_offload.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

Comments

David Laight Sept. 29, 2023, 8:10 a.m. UTC | #1 
From: joao@overdrivepizza.com
> Sent: 27 September 2023 03:02
> 
> From: Joao Moreira <joao.moreira@intel.com>
> 
> Currently, 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, make it unsigned and
> also check if it reaches UINT_MAX when being incremented.
> 
> After checking with maintainers, it was mentioned that front-end will
> cap the num_actions value and that it is not possible to reach such
> condition for an overflow. 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/netfilter/nf_tables_offload.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/net/netfilter/nf_tables_offload.c b/net/netfilter/nf_tables_offload.c
> index 12ab78fa5d84..d25088791a74 100644
> --- a/net/netfilter/nf_tables_offload.c
> +++ b/net/netfilter/nf_tables_offload.c
> @@ -90,7 +90,8 @@ struct nft_flow_rule *nft_flow_rule_create(struct net *net,
>  {
>  	struct nft_offload_ctx *ctx;
>  	struct nft_flow_rule *flow;
> -	int num_actions = 0, err;
> +	unsigned int num_actions = 0;
> +	int err;
>  	struct nft_expr *expr;
> 
>  	expr = nft_expr_first(rule);
> @@ -99,6 +100,9 @@ struct nft_flow_rule *nft_flow_rule_create(struct net *net,
>  		    expr->ops->offload_action(expr))
>  			num_actions++;
> 
> +		if (num_actions == UINT_MAX)
> +			return ERR_PTR(-ENOMEM);
> +
>  		expr = nft_expr_next(expr);

The code is going to 'crash and burn' well before the counter
can possibly overflow.

nft_expr_next() is ((void *)expr) + expr->ops->size;

It is far more likely that has got setup wrong than the
count is too big. 

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
diff mbox series

Patch

diff --git a/net/netfilter/nf_tables_offload.c b/net/netfilter/nf_tables_offload.c
index 12ab78fa5d84..d25088791a74 100644
--- a/net/netfilter/nf_tables_offload.c
+++ b/net/netfilter/nf_tables_offload.c
@@ -90,7 +90,8 @@  struct nft_flow_rule *nft_flow_rule_create(struct net *net,
 {
 	struct nft_offload_ctx *ctx;
 	struct nft_flow_rule *flow;
-	int num_actions = 0, err;
+	unsigned int num_actions = 0;
+	int err;
 	struct nft_expr *expr;
 
 	expr = nft_expr_first(rule);
@@ -99,6 +100,9 @@  struct nft_flow_rule *nft_flow_rule_create(struct net *net,
 		    expr->ops->offload_action(expr))
 			num_actions++;
 
+		if (num_actions == UINT_MAX)
+			return ERR_PTR(-ENOMEM);
+
 		expr = nft_expr_next(expr);
 	}