linux-kernel - Re: [PATCH net-next] netfilter: arptables: use xt_entry_foreach() in copy_entries_to

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Message-ID: <aXERRqh79pmVsuzk@horms.kernel.org>
Date: Wed, 21 Jan 2026 17:47:50 +0000
From: Simon Horman <horms@...nel.org>
To: Kshitiz Bartariya <kshitiz.bartariya@...omail.in>
Cc: Pablo Neira Ayuso <pablo@...filter.org>,
	Florian Westphal <fw@...len.de>, Phil Sutter <phil@....cc>,
	"David S . Miller" <davem@...emloft.net>,
	David Ahern <dsahern@...nel.org>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	netfilter-devel@...r.kernel.org, coreteam@...filter.org,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] netfilter: arptables: use xt_entry_foreach() in
 copy_entries_to_user()

On Mon, Jan 19, 2026 at 12:07:04PM +0530, Kshitiz Bartariya wrote:
> Replace the manual offset-based iteration with xt_entry_foreach(),
> thereby removing FIXME. The byte offset semantics and user ABI
> are preserved.
> 
> Signed-off-by: Kshitiz Bartariya <kshitiz.bartariya@...omail.in>
> ---
>  net/ipv4/netfilter/arp_tables.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/net/ipv4/netfilter/arp_tables.c b/net/ipv4/netfilter/arp_tables.c
> index 1cdd9c28ab2d..9f82ce0fcaa5 100644
> --- a/net/ipv4/netfilter/arp_tables.c
> +++ b/net/ipv4/netfilter/arp_tables.c
> @@ -684,12 +684,11 @@ static int copy_entries_to_user(unsigned int total_size,
>  
>  	loc_cpu_entry = private->entries;
>  
> -	/* FIXME: use iterator macros --RR */
> -	/* ... then go back and fix counters and names */
> -	for (off = 0, num = 0; off < total_size; off += e->next_offset, num++){
> +	num = 0;
> +	xt_entry_foreach(e, loc_cpu_entry, total_size) {
>  		const struct xt_entry_target *t;
>  
> -		e = loc_cpu_entry + off;
> +		off = (unsigned char *)e - (unsigned char *)loc_cpu_entry;

This offset calculation makes me feel queasy.

Can the code start with off = 0 and increment it by e->next_offset
as the loop iterates, as was the case before this patch?
It would be similar to how num is handled.

>  		if (copy_to_user(userptr + off, e, sizeof(*e))) {
>  			ret = -EFAULT;
>  			goto free_counters;
> @@ -707,6 +706,7 @@ static int copy_entries_to_user(unsigned int total_size,
>  			ret = -EFAULT;
>  			goto free_counters;
>  		}
> +		num++;
>  	}
>  
>   free_counters:
> -- 
> 2.50.1 (Apple Git-155)
>