Re: [PATCH] net: sched: Annotate struct tc_pedit with __counted_by

[Gustavo A. R. Silva]

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@xxxxxxxxxxxx>
> ---
> Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
> Cc: Jamal Hadi Salim <jhs@xxxxxxxxxxxx>
> Cc: Cong Wang <xiyou.wangcong@xxxxxxxxx>
> Cc: Jiri Pirko <jiri@xxxxxxxxxxx>
> Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
> Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
> Cc: Paolo Abeni <pabeni@xxxxxxxxxx>
> Cc: "Gustavo A. R. Silva" <gustavoars@xxxxxxxxxx>
> Cc: netdev@xxxxxxxxxxxxxxx
> Cc: linux-hardening@xxxxxxxxxxxxxxx

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

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

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;