netdev - Re: [PATCH] net/packet: Annotate struct packet_fanout with __counted

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Date: Wed, 4 Oct 2023 01:34:37 +0200
From: "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To: Kees Cook <keescook@...omium.org>, "David S. Miller" <davem@...emloft.net>
Cc: Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
 Paolo Abeni <pabeni@...hat.com>, Willem de Bruijn <willemb@...gle.com>,
 Anqi Shen <amy.saq@...group.com>, netdev@...r.kernel.org,
 "Gustavo A. R. Silva" <gustavoars@...nel.org>,
 Nathan Chancellor <nathan@...nel.org>,
 Nick Desaulniers <ndesaulniers@...gle.com>, Tom Rix <trix@...hat.com>,
 syzbot <syzkaller@...glegroups.com>, Jianfeng Tan <henry.tjf@...group.com>,
 linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org,
 llvm@...ts.linux.dev
Subject: Re: [PATCH] net/packet: Annotate struct packet_fanout with
 __counted_by

On 10/4/23 01:17, Kees Cook 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 via CONFIG_UBSAN_BOUNDS (for
> array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> functions).
> 
> As found with Coccinelle[1], add __counted_by for struct packet_fanout.
> 
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Eric Dumazet <edumazet@...gle.com>
> Cc: Jakub Kicinski <kuba@...nel.org>
> Cc: Paolo Abeni <pabeni@...hat.com>
> Cc: Willem de Bruijn <willemb@...gle.com>
> Cc: Anqi Shen <amy.saq@...group.com>
> Cc: netdev@...r.kernel.org
> Link: https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci [1]
> Signed-off-by: Kees Cook <keescook@...omium.org>

Reviewed-by: Gustavo A. R. Silva <gustavoars@...nel.org>

Thanks
--
Gustavo

> ---
>   net/packet/internal.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/packet/internal.h b/net/packet/internal.h
> index 63f4865202c1..d29c94c45159 100644
> --- a/net/packet/internal.h
> +++ b/net/packet/internal.h
> @@ -94,7 +94,7 @@ struct packet_fanout {
>   	spinlock_t		lock;
>   	refcount_t		sk_ref;
>   	struct packet_type	prot_hook ____cacheline_aligned_in_smp;
> -	struct sock	__rcu	*arr[];
> +	struct sock	__rcu	*arr[] __counted_by(max_num_members);
>   };
>   
>   struct packet_rollover {