Re: [PATCH net-next v5] net: ipv6: seg6: report lwtunnel setup errors via extack

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

Hi Gabriel,
On Fri, Oct 09, 2026 at 05:20:13PM +0200, Gabriel Goller wrote:
> seg6_build_state() rejected invalid configurations with a generic -EINVAL,
> so "ip route add ... encap seg6 ..." sometimes reported "Invalid argument".
> 
> Add extack messages to the checks that lacked one, and use
> NL_REQ_ATTR_CHECK() for the missing SRH attribute so that userspace can
> tell which attribute is missing. The checks themselves and their return
> values are unchanged.
> 
> Signed-off-by: Gabriel Goller <g.goller@proxmox.com>
> ---
> 
> v5 (https://lore.kernel.org/all/20261005140637.644840-1-g.goller@proxmox.com/):
>  * use NL_REQ_ATTR_CHECK() for the missing SRH attribute (Jakub)
>  * reword the inline mode message to "inline mode requires the IPv6
>    address family", since it also applies to IPv4 nexthop objects
>    (Andrea)
>  * consistently call the header "IPv6 Segment Routing Header" (RFC 8754)
>    in all messages (Andrea)
>  * include the offending mode value in the invalid mode message
>  * reword the commit message to match
> 
> v4 (https://lore.kernel.org/all/20260923120228.172643-1-g.goller@proxmox.com/):
>  * use NL_SET_ERR_MSG when the SRH attr is missing
>  * use NL_SET_ERR_MSG_ATTR when we have an invalid attr
> 
> 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 | 26 +++++++++++++++++++++-----
>  1 file changed, 21 insertions(+), 5 deletions(-)
> 
> diff --git a/net/ipv6/seg6_iptunnel.c b/net/ipv6/seg6_iptunnel.c
> index 69a6ef5c5317..0d39a38a5dd2 100644
> --- a/net/ipv6/seg6_iptunnel.c
> +++ b/net/ipv6/seg6_iptunnel.c
> @@ -762,8 +762,11 @@ 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);
> @@ -771,7 +774,7 @@ static int seg6_build_state(struct net *net, struct nlattr *nla,
>  	if (err < 0)
>  		return err;
>  
> -	if (!tb[SEG6_IPTUNNEL_SRH])
> +	if (NL_REQ_ATTR_CHECK(extack, nla, tb, SEG6_IPTUNNEL_SRH))
>  		return -EINVAL;
>  
>  	tuninfo = nla_data(tb[SEG6_IPTUNNEL_SRH]);
> @@ -782,13 +785,19 @@ 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_ATTR(extack, tb[SEG6_IPTUNNEL_SRH],
> +				    "truncated IPv6 Segment Routing Header attribute");
>  		return -EINVAL;
> +	}
>  
>  	switch (tuninfo->mode) {
>  	case SEG6_IPTUN_MODE_INLINE:
> -		if (family != AF_INET6)
> +		if (family != AF_INET6) {
> +			NL_SET_ERR_MSG_ATTR(extack, tb[SEG6_IPTUNNEL_SRH],
> +					    "inline mode requires the IPv6 address family");
>  			return -EINVAL;
> +		}
>  
>  		if (tb[SEG6_IPTUNNEL_SRC]) {
>  			NL_SET_ERR_MSG(extack, "incompatible mode for tunsrc");
> @@ -804,12 +813,19 @@ static int seg6_build_state(struct net *net, struct nlattr *nla,
>  	case SEG6_IPTUN_MODE_L2ENCAP_RED:
>  		break;
>  	default:
> +		NL_SET_ERR_MSG_ATTR_FMT(extack, tb[SEG6_IPTUNNEL_SRH],
> +					"invalid SRv6 encapsulation mode %d",
> +					tuninfo->mode);
>  		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_ATTR(extack, tb[SEG6_IPTUNNEL_SRH],
> +				    "invalid IPv6 Segment Routing Header");
>  		return -EINVAL;
> +	}
>  
>  	newts = lwtunnel_state_alloc(tuninfo_len + sizeof(*slwt));
>  	if (!newts)
> -- 
> 2.47.3
> 
> 

Thanks for the update.

Reviewed-by: Hangbin Liu <liuhangbin@kylinos.cn>