netdev - Re: [PATCH net-next v4 1/7] ipv6: Check of max HBH or DestOp sysctl is zero and drop if it is

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Message-ID: <30e7ea41-ed0f-4049-b844-b0d0507deedb@gmail.com>
Date: Fri, 23 Jan 2026 22:16:30 +0100
From: Justin Iurman <justin.iurman@...il.com>
To: Tom Herbert <tom@...bertland.com>, davem@...emloft.net, kuba@...nel.org,
 netdev@...r.kernel.org
Subject: Re: [PATCH net-next v4 1/7] ipv6: Check of max HBH or DestOp sysctl
 is zero and drop if it is

On 1/21/26 22:49, Tom Herbert wrote:
> In IPv6 Destination options processing function check if
> net->ipv6.sysctl.max_dst_opts_cnt is zero up front. If it is zero then
> drop the packet since Destination Options processing is disabled.
> 
> Similarly, in IPv6 hop-by-hop options processing function check if
> net->ipv6.sysctl.max_hbh_opts_cnt is zero up front. If it is zero then
> drop the packet since Hop-by-Hop Options processing is disabled.
> 
> Signed-off-by: Tom Herbert <tom@...bertland.com>
> ---
>   net/ipv6/exthdrs.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/net/ipv6/exthdrs.c b/net/ipv6/exthdrs.c
> index 54088fa0c09d..45bbad76f5de 100644
> --- a/net/ipv6/exthdrs.c
> +++ b/net/ipv6/exthdrs.c
> @@ -303,7 +303,8 @@ static int ipv6_destopt_rcv(struct sk_buff *skb)
>   	struct net *net = dev_net(skb->dev);
>   	int extlen;
>   
> -	if (!pskb_may_pull(skb, skb_transport_offset(skb) + 8) ||
> +	if (!net->ipv6.sysctl.max_dst_opts_cnt ||
> +	    !pskb_may_pull(skb, skb_transport_offset(skb) + 8) ||
>   	    !pskb_may_pull(skb, (skb_transport_offset(skb) +
>   				 ((skb_transport_header(skb)[1] + 1) << 3)))) {
>   		__IP6_INC_STATS(dev_net(dst_dev(dst)), idev,

Hi Tom,

You should use READ_ONCE() and store it:

int max_dst_opts_cnt = READ_ONCE(net->ipv6.sysctl.max_dst_opts_cnt);

if (!max_dst_opts_cnt || ...)

[...]

if (ip6_parse_tlv(false, skb, max_dst_opts_cnt)) {

> @@ -1041,7 +1042,8 @@ int ipv6_parse_hopopts(struct sk_buff *skb)
>   	 * sizeof(struct ipv6hdr) by definition of
>   	 * hop-by-hop options.
>   	 */
> -	if (!pskb_may_pull(skb, sizeof(struct ipv6hdr) + 8) ||
> +	if (!net->ipv6.sysctl.max_hbh_opts_cnt ||
> +	    !pskb_may_pull(skb, sizeof(struct ipv6hdr) + 8) ||
>   	    !pskb_may_pull(skb, (sizeof(struct ipv6hdr) +
>   				 ((skb_transport_header(skb)[1] + 1) << 3)))) {
>   fail_and_free:

Same remark for max_hbh_opts_cnt.