netdev - Re: [PATCH net-next v5 1/7] ipv6: Check of max HBH or DestOp sysctl is zero and drop if it is

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Message-ID: <6ad428fe-bdfb-41a6-baaf-786663e2223d@gmail.com>
Date: Tue, 27 Jan 2026 18:50:26 +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 v5 1/7] ipv6: Check of max HBH or DestOp sysctl
 is zero and drop if it is

On 1/26/26 20:48, 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 | 18 ++++++++++--------
>   1 file changed, 10 insertions(+), 8 deletions(-)
> 
> diff --git a/net/ipv6/exthdrs.c b/net/ipv6/exthdrs.c
> index 54088fa0c09d..b9d186784b96 100644
> --- a/net/ipv6/exthdrs.c
> +++ b/net/ipv6/exthdrs.c
> @@ -301,9 +301,11 @@ static int ipv6_destopt_rcv(struct sk_buff *skb)
>   #endif
>   	struct dst_entry *dst = skb_dst(skb);
>   	struct net *net = dev_net(skb->dev);
> -	int extlen;
> +	int extlen, max_opts_cnt;
>   
> -	if (!pskb_may_pull(skb, skb_transport_offset(skb) + 8) ||
> +	max_opts_cnt = READ_ONCE(net->ipv6.sysctl.max_dst_opts_cnt);
> +	if (!max_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,
> @@ -322,8 +324,7 @@ static int ipv6_destopt_rcv(struct sk_buff *skb)
>   	dstbuf = opt->dst1;
>   #endif
>   
> -	if (ip6_parse_tlv(false, skb,
> -			  READ_ONCE(net->ipv6.sysctl.max_dst_opts_cnt))) {
> +	if (ip6_parse_tlv(false, skb, max_opts_cnt)) {
>   		skb->transport_header += extlen;
>   		opt = IP6CB(skb);
>   #if IS_ENABLED(CONFIG_IPV6_MIP6)
> @@ -1033,7 +1034,7 @@ int ipv6_parse_hopopts(struct sk_buff *skb)
>   {
>   	struct inet6_skb_parm *opt = IP6CB(skb);
>   	struct net *net = dev_net(skb->dev);
> -	int extlen;
> +	int extlen, max_opts_cnt;
>   
>   	/*
>   	 * skb_network_header(skb) is equal to skb->data, and
> @@ -1041,7 +1042,9 @@ 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) ||
> +	max_opts_cnt = READ_ONCE(net->ipv6.sysctl.max_hbh_opts_cnt);
> +	if (!max_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:
> @@ -1054,8 +1057,7 @@ int ipv6_parse_hopopts(struct sk_buff *skb)
>   		goto fail_and_free;
>   
>   	opt->flags |= IP6SKB_HOPBYHOP;
> -	if (ip6_parse_tlv(true, skb,
> -			  READ_ONCE(net->ipv6.sysctl.max_hbh_opts_cnt))) {
> +	if (ip6_parse_tlv(true, skb, max_opts_cnt)) {
>   		skb->transport_header += extlen;
>   		opt = IP6CB(skb);
>   		opt->nhoff = sizeof(struct ipv6hdr);

Reviewed-by: Justin Iurman <justin.iurman@...il.com>