linux-kernel - Re: [PATCH] net: sched: Annotate struct tc_pedit with __counted

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Date: Fri, 16 Feb 2024 18:04:14 -0600
From: "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To: Kees Cook <keescook@...omium.org>, Jakub Kicinski <kuba@...nel.org>
Cc: Jamal Hadi Salim <jhs@...atatu.com>, Cong Wang
 <xiyou.wangcong@...il.com>, Jiri Pirko <jiri@...nulli.us>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Paolo Abeni <pabeni@...hat.com>, "Gustavo A. R. Silva"
 <gustavoars@...nel.org>, netdev@...r.kernel.org,
 linux-hardening@...r.kernel.org, Nathan Chancellor <nathan@...nel.org>,
 Nick Desaulniers <ndesaulniers@...gle.com>, Bill Wendling
 <morbo@...gle.com>, Justin Stitt <justinstitt@...gle.com>,
 linux-kernel@...r.kernel.org, llvm@...ts.linux.dev
Subject: Re: [PATCH] net: sched: Annotate struct tc_pedit with __counted_by



On 2/16/24 17:27, 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 checking 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 tc_pedit.
> Additionally, since the element count member must be set before accessing
> the annotated flexible array member, move its initialization earlier.
> 
> Link: https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci [1]
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
> Cc: Jakub Kicinski <kuba@...nel.org>
> Cc: Jamal Hadi Salim <jhs@...atatu.com>
> Cc: Cong Wang <xiyou.wangcong@...il.com>
> Cc: Jiri Pirko <jiri@...nulli.us>
> Cc: "David S. Miller" <davem@...emloft.net>
> 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
> Cc: linux-hardening@...r.kernel.org

`opt->nkeys` updated before `memcpy()`, looks good to me:

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

Thanks!
--
Gustavo

> ---
>   include/uapi/linux/tc_act/tc_pedit.h | 2 +-
>   net/sched/act_pedit.c                | 2 +-
>   2 files changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/include/uapi/linux/tc_act/tc_pedit.h b/include/uapi/linux/tc_act/tc_pedit.h
> index f3e61b04fa01..f5cab7fc96ab 100644
> --- a/include/uapi/linux/tc_act/tc_pedit.h
> +++ b/include/uapi/linux/tc_act/tc_pedit.h
> @@ -62,7 +62,7 @@ struct tc_pedit_sel {
>   	tc_gen;
>   	unsigned char           nkeys;
>   	unsigned char           flags;
> -	struct tc_pedit_key     keys[0];
> +	struct tc_pedit_key     keys[] __counted_by(nkeys);
>   };
>   
>   #define tc_pedit tc_pedit_sel
> diff --git a/net/sched/act_pedit.c b/net/sched/act_pedit.c
> index 2ef22969f274..21e863d2898c 100644
> --- a/net/sched/act_pedit.c
> +++ b/net/sched/act_pedit.c
> @@ -515,11 +515,11 @@ static int tcf_pedit_dump(struct sk_buff *skb, struct tc_action *a,
>   		spin_unlock_bh(&p->tcf_lock);
>   		return -ENOBUFS;
>   	}
> +	opt->nkeys = parms->tcfp_nkeys;
>   
>   	memcpy(opt->keys, parms->tcfp_keys,
>   	       flex_array_size(opt, keys, parms->tcfp_nkeys));
>   	opt->index = p->tcf_index;
> -	opt->nkeys = parms->tcfp_nkeys;
>   	opt->flags = parms->tcfp_flags;
>   	opt->action = p->tcf_action;
>   	opt->refcnt = refcount_read(&p->tcf_refcnt) - ref;