Re: [PATCH 14/14] net: sched: Annotate struct tc_pedit with __counted_by

[Kees Cook]

On Fri, Sep 22, 2023 at 10:28:56AM -0700, 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.
> 
> [1] https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci
> 
> 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: Jakub Kicinski <kuba@xxxxxxxxxx>
> Cc: Paolo Abeni <pabeni@xxxxxxxxxx>
> Cc: netdev@xxxxxxxxxxxxxxx
> Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> ---
>  net/sched/act_pedit.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/sched/act_pedit.c b/net/sched/act_pedit.c
> index 1ef8fcfa9997..77c407eff3b0 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;
> -- 
> 2.34.1
> 

Coccinelle was not happy about the #define ...

struct tc_pedit_sel {
	tc_gen;
	unsigned char           nkeys;
	unsigned char           flags;
	struct tc_pedit_key     keys[0];
};

#define tc_pedit tc_pedit_sel

Also, it's not been converted to a proper flexible array...

-- 
Kees Cook