Subject: Re: [PATCH v2 2/2] net: openvswitch: Annotate struct mask_array with __counted_by

From: Kees Cook <[email-masked]>
Date: Sat, 14 Oct 2023 19:29:57 -0700

On Sat, Oct 14, 2023 at 08:34:53AM +0200, Christophe JAILLET wrote:
> Prepare for the coming implementation by GCC and Clang of the __counted_by
> attribute. Flexible array members annotated with __counted_by can have
> their accesses bounds-checked at run-time checking via CONFIG_UBSAN_BOUNDS
> (for array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> functions).
> 
> Signed-off-by: Christophe JAILLET <[email-masked]>
> ---
> v2: Fix the subject  [Ilya Maximets]
>     fix the field name used with __counted_by  [Ilya Maximets]
> 
> v1: https://lore.kernel.org/all/f66ddcf1ef[email-masked]/
> 
> 
> This patch is part of a work done in parallel of what is currently worked
> on by Kees Cook.
> 
> My patches are only related to corner cases that do NOT match the
> semantic of his Coccinelle script[1].
> 
> In this case, in tbl_mask_array_alloc(), several things are allocated with
> a single allocation. Then, some pointer arithmetic computes the address of
> the memory after the flex-array.
> 
> [1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci
> ---
>  net/openvswitch/flow_table.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/openvswitch/flow_table.h b/net/openvswitch/flow_table.h
> index 9e659db78c05..f524dc3e4862 100644
> --- a/net/openvswitch/flow_table.h
> +++ b/net/openvswitch/flow_table.h
> @@ -48,7 +48,7 @@ struct mask_array {
>  	int count, max;
>  	struct mask_array_stats __percpu *masks_usage_stats;
>  	u64 *masks_usage_zero_cntr;
> -	struct sw_flow_mask __rcu *masks[];
> +	struct sw_flow_mask __rcu *masks[] __counted_by(max);
>  };

Yup, this looks correct to me. Thanks!

Reviewed-by: Kees Cook <[email-masked]>

-- 
Kees Cook