netdev - Re: [PATCH] ipv4/fib: Replace zero-length array with DECLARE_FLEX

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Date:   Thu, 17 Nov 2022 22:29:36 -0600
From:   "Gustavo A. R. Silva" <gustavoars@...nel.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        David Ahern <dsahern@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] ipv4/fib: Replace zero-length array with
 DECLARE_FLEX_ARRAY() helper

On Thu, Nov 17, 2022 at 08:21:52PM -0800, Kees Cook wrote:
> Zero-length arrays are deprecated[1] and are being replaced with
> flexible array members in support of the ongoing efforts to tighten the
> FORTIFY_SOURCE routines on memcpy(), correctly instrument array indexing
> with UBSAN_BOUNDS, and to globally enable -fstrict-flex-arrays=3.
> 
> Replace zero-length array with flexible-array member in struct key_vector.
> 
> This results in no differences in binary output.
> 
> [1] https://github.com/KSPP/linux/issues/78
> 
> Cc: Jakub Kicinski <kuba@...nel.org>
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>
> Cc: David Ahern <dsahern@...nel.org>
> Cc: Eric Dumazet <edumazet@...gle.com>
> Cc: Paolo Abeni <pabeni@...hat.com>
> Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>
> Cc: netdev@...r.kernel.org
> Signed-off-by: Kees Cook <keescook@...omium.org>

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

Thanks!
--
Gustavo

> ---
>  net/ipv4/fib_trie.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/ipv4/fib_trie.c b/net/ipv4/fib_trie.c
> index 452ff177e4da..c88bf856c443 100644
> --- a/net/ipv4/fib_trie.c
> +++ b/net/ipv4/fib_trie.c
> @@ -126,7 +126,7 @@ struct key_vector {
>  		/* This list pointer if valid if (pos | bits) == 0 (LEAF) */
>  		struct hlist_head leaf;
>  		/* This array is valid if (pos | bits) > 0 (TNODE) */
> -		struct key_vector __rcu *tnode[0];
> +		DECLARE_FLEX_ARRAY(struct key_vector __rcu *, tnode);
>  	};
>  };
>  
> -- 
> 2.34.1
>