Re: [PATCH net-next v3] net: ipv6: seg6: report lwtunnel setup errors via extack

[Hangbin Liu <hangbin.liu@linux.dev>]

Hi Gabriel,
On Wed, Sep 23, 2026 at 02:02:04PM +0200, Gabriel Goller wrote:
> seg6_build_state() rejected invalid configurations with a generic -EINVAL,
> so "ip route add ... encap seg6 ..." always reported "Invalid argument".
> 
> Attach an extack message to each of them. The checks themselves and their
> return values are unchanged.
> 
> Signed-off-by: Gabriel Goller <g.goller@proxmox.com>
> ---
> 
> v3 (https://lore.kernel.org/all/20260922090851.38978-1-g.goller@proxmox.com/):
>  * format fix
>  * use NL_SET_ERR_MSG_ATTR
> 
> v2 (https://lore.kernel.org/all/20260918153544.1178884-1-g.goller@proxmox.com/):
>  * dropped tests
> 
>  net/ipv6/seg6_iptunnel.c | 24 +++++++++++++++++++-----
>  1 file changed, 19 insertions(+), 5 deletions(-)
> 
> diff --git a/net/ipv6/seg6_iptunnel.c b/net/ipv6/seg6_iptunnel.c
> index 61c6a27bf202..9f1aecc4f215 100644
> --- a/net/ipv6/seg6_iptunnel.c
> +++ b/net/ipv6/seg6_iptunnel.c
> @@ -756,8 +756,11 @@ static int seg6_build_state(struct net *net, struct nlattr *nla,
>  	struct seg6_lwt *slwt;
>  	int err;
>  
> -	if (family != AF_INET && family != AF_INET6)
> +	if (family != AF_INET && family != AF_INET6) {
> +		NL_SET_ERR_MSG(extack,
> +			       "unsupported address family for SRv6 encapsulation");
>  		return -EINVAL;
> +	}
>  
>  	err = nla_parse_nested_deprecated(tb, SEG6_IPTUNNEL_MAX, nla,
>  					  seg6_iptunnel_policy, extack);
> @@ -765,8 +768,10 @@ static int seg6_build_state(struct net *net, struct nlattr *nla,
>  	if (err < 0)
>  		return err;
>  
> -	if (!tb[SEG6_IPTUNNEL_SRH])
> +	if (!tb[SEG6_IPTUNNEL_SRH]) {
> +		NL_SET_ERR_MSG_ATTR(extack, nla, "missing SRv6 SRH attribute");
>  		return -EINVAL;

My bad. NL_SET_ERR_MSG_ATTR expects the specific attr. In this error path,
there is no tb[SEG6_IPTUNNEL_SRH]. So we can keep using NL_SET_ERR_MSG().

> +	}
>  
>  	tuninfo = nla_data(tb[SEG6_IPTUNNEL_SRH]);
>  	tuninfo_len = nla_len(tb[SEG6_IPTUNNEL_SRH]);
> @@ -776,13 +781,18 @@ static int seg6_build_state(struct net *net, struct nlattr *nla,
>  	 */
>  	min_size = sizeof(*tuninfo) + sizeof(struct ipv6_sr_hdr) +
>  		   sizeof(struct in6_addr);
> -	if (tuninfo_len < min_size)
> +	if (tuninfo_len < min_size) {
> +		NL_SET_ERR_MSG(extack, "truncated SRv6 SRH attribute");

And here I think we can use like

	NL_SET_ERR_MSG_ATTR(extact, tb[SEG6_IPTUNNEL_SRH], "truncated ...")

>  		return -EINVAL;
> +	}
>  
>  	switch (tuninfo->mode) {
>  	case SEG6_IPTUN_MODE_INLINE:
> -		if (family != AF_INET6)
> +		if (family != AF_INET6) {
> +			NL_SET_ERR_MSG(extack,
> +				       "inline mode requires an IPv6 route");

Same here

	NL_SET_ERR_MSG_ATTR(extact, tb[SEG6_IPTUNNEL_SRH], "inline ...")

>  			return -EINVAL;
> +		}
>  
>  		if (tb[SEG6_IPTUNNEL_SRC]) {
>  			NL_SET_ERR_MSG(extack, "incompatible mode for tunsrc");
> @@ -798,12 +808,16 @@ static int seg6_build_state(struct net *net, struct nlattr *nla,
>  	case SEG6_IPTUN_MODE_L2ENCAP_RED:
>  		break;
>  	default:
> +		NL_SET_ERR_MSG(extack, "invalid SRv6 encapsulation mode");

And here.

>  		return -EINVAL;
>  	}
>  
>  	/* verify that SRH is consistent */
> -	if (!seg6_validate_srh(tuninfo->srh, tuninfo_len - sizeof(*tuninfo), false))
> +	if (!seg6_validate_srh(tuninfo->srh, tuninfo_len - sizeof(*tuninfo),
> +			       false)) {
> +		NL_SET_ERR_MSG(extack, "invalid SRv6 segment routing header");
>  		return -EINVAL;
> +	}

Here.

Thanks
Hangbin