Re: [PATCH v1 net 2/2] fou: Don't allow 0 for FOU_ATTR_IPPROTO.

[Jakub Kicinski <kuba@kernel.org>]

On Mon, 12 Jan 2026 20:06:36 +0000 Kuniyuki Iwashima wrote:
> fou_udp_recv() has the same problem mentioned in the previous
> patch.
> 
> If FOU_ATTR_IPPROTO is set to 0, skb is not freed by
> fou_udp_recv() nor "resubmit"-ted in ip_protocol_deliver_rcu().
> 
> Let's forbid 0 for FOU_ATTR_IPPROTO.
> 
> Fixes: 23461551c0062 ("fou: Support for foo-over-udp RX path")
> Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
> ---
>  net/ipv4/fou_nl.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/ipv4/fou_nl.c b/net/ipv4/fou_nl.c
> index 7a99639204b16..0dec9da1bff46 100644
> --- a/net/ipv4/fou_nl.c
> +++ b/net/ipv4/fou_nl.c
> @@ -15,7 +15,7 @@
>  const struct nla_policy fou_nl_policy[FOU_ATTR_IFINDEX + 1] = {
>  	[FOU_ATTR_PORT] = { .type = NLA_BE16, },
>  	[FOU_ATTR_AF] = { .type = NLA_U8, },
> -	[FOU_ATTR_IPPROTO] = { .type = NLA_U8, },
> +	[FOU_ATTR_IPPROTO] = { .type = NLA_U8, .min = 1 },
>  	[FOU_ATTR_TYPE] = { .type = NLA_U8, },
>  	[FOU_ATTR_REMCSUM_NOPARTIAL] = { .type = NLA_FLAG, },
>  	[FOU_ATTR_LOCAL_V4] = { .type = NLA_U32, },

This code is generated, please use :

diff --git a/Documentation/netlink/specs/fou.yaml b/Documentation/netlink/specs/fou.yaml
index 8e7974ec453f..331f1b342b3a 100644
--- a/Documentation/netlink/specs/fou.yaml
+++ b/Documentation/netlink/specs/fou.yaml
@@ -39,6 +39,8 @@ kernel-policy: global
       -
         name: ipproto
         type: u8
+        checks:
+          min: 1
       -
         name: type
         type: u8
diff --git a/net/ipv4/fou_nl.c b/net/ipv4/fou_nl.c
index 7a99639204b1..309d5ba983d0 100644
--- a/net/ipv4/fou_nl.c
+++ b/net/ipv4/fou_nl.c
@@ -15,7 +15,7 @@
 const struct nla_policy fou_nl_policy[FOU_ATTR_IFINDEX + 1] = {
 	[FOU_ATTR_PORT] = { .type = NLA_BE16, },
 	[FOU_ATTR_AF] = { .type = NLA_U8, },
-	[FOU_ATTR_IPPROTO] = { .type = NLA_U8, },
+	[FOU_ATTR_IPPROTO] = NLA_POLICY_MIN(NLA_U8, 1),
 	[FOU_ATTR_TYPE] = { .type = NLA_U8, },
 	[FOU_ATTR_REMCSUM_NOPARTIAL] = { .type = NLA_FLAG, },
 	[FOU_ATTR_LOCAL_V4] = { .type = NLA_U32, },