Subject: Re: [PATCH net-next] net: make sure we never create ifindex = 0

From: Leon Romanovsky <[email-masked]>
Date: Sun, 30 Jul 2023 16:32:19 +0300

On Fri, Jul 28, 2023 at 06:56:23PM -0700, Jakub Kicinski wrote:
> Instead of allocating from 1 use proper xa_limit, to protect
> ourselves from IDs wrapping back to 0.
> 
> Fixes: 759ab1edb56c ("net: store netdevs in an xarray")
> Reported-by: Stephen Hemminger <[email-masked]>
> Link: https://lore.kernel.org/all/[email-masked]/
> Signed-off-by: Jakub Kicinski <[email-masked]>
> ---
> CC: [email-masked]
> ---
>  net/core/dev.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/net/core/dev.c b/net/core/dev.c
> index b58674774a57..2312ca67b95e 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -9587,7 +9587,8 @@ static int dev_index_reserve(struct net *net, u32 ifindex)
>  
>  	if (!ifindex)
>  		err = xa_alloc_cyclic(&net->dev_by_index, &ifindex, NULL,
> -				      xa_limit_31b, &net->ifindex, GFP_KERNEL);
> +				      XA_LIMIT(1, INT_MAX), &net->ifindex,
> +				      GFP_KERNEL);
>  	else
>  		err = xa_insert(&net->dev_by_index, ifindex, NULL, GFP_KERNEL);
>  	if (err < 0)
> @@ -11271,7 +11272,6 @@ static int __net_init netdev_init(struct net *net)
>  	if (net->dev_index_head == NULL)
>  		goto err_idx;
>  
> -	net->ifindex = 1;
>  	xa_init_flags(&net->dev_by_index, XA_FLAGS_ALLOC);

You don't need to change xa_limit_31b, just change XA_FLAGS_ALLOC to be XA_FLAGS_ALLOC1
and allocations will start from 1.

Thanks

>  
>  	RAW_INIT_NOTIFIER_HEAD(&net->netdev_chain);
> -- 
> 2.41.0
>