While fixing the binary min-len implementaion, I noticed that
the only user, should AFAICT be using exact-len instead.

In net/ipv4/fou_core.c FOU_ATTR_LOCAL_V6 and FOU_ATTR_PEER_V6
are only used for singular IPv6 addresses, a exact-len policy,
therefore seams like a better fit.

AFAICT this was caused by lacking support for the exact-len check
at the time of the blamed commit, which was later remedied by
c63ad379526 ("tools: ynl-gen: add support for exact-len validation").

This patch therefore changes the local-v6/peer-v6 attributes to
use an exact-len check, instead of a min-len check.

Fixes: 4eb77b4ecd3c ("netlink: add a proto specification for FOU")
Signed-off-by: Asbjørn Sloth Tønnesen <ast@fiberby.net>
---
 Documentation/netlink/specs/fou.yaml | 4 ++--
 net/ipv4/fou_nl.c                    | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/Documentation/netlink/specs/fou.yaml b/Documentation/netlink/specs/fou.yaml
index 57735726262ec..8e7974ec453fc 100644
--- a/Documentation/netlink/specs/fou.yaml
+++ b/Documentation/netlink/specs/fou.yaml
@@ -52,7 +52,7 @@ attribute-sets:
         name: local-v6
         type: binary
         checks:
-          min-len: 16
+          exact-len: 16
       -
         name: peer-v4
         type: u32
@@ -60,7 +60,7 @@ attribute-sets:
         name: peer-v6
         type: binary
         checks:
-          min-len: 16
+          exact-len: 16
       -
         name: peer-port
         type: u16
diff --git a/net/ipv4/fou_nl.c b/net/ipv4/fou_nl.c
index 3d9614609b2d3..506260b4a4dc2 100644
--- a/net/ipv4/fou_nl.c
+++ b/net/ipv4/fou_nl.c
@@ -18,9 +18,9 @@ const struct nla_policy fou_nl_policy[FOU_ATTR_IFINDEX + 1] = {
 	[FOU_ATTR_TYPE] = { .type = NLA_U8, },
 	[FOU_ATTR_REMCSUM_NOPARTIAL] = { .type = NLA_FLAG, },
 	[FOU_ATTR_LOCAL_V4] = { .type = NLA_U32, },
-	[FOU_ATTR_LOCAL_V6] = { .len = 16, },
+	[FOU_ATTR_LOCAL_V6] = NLA_POLICY_EXACT_LEN(16),
 	[FOU_ATTR_PEER_V4] = { .type = NLA_U32, },
-	[FOU_ATTR_PEER_V6] = { .len = 16, },
+	[FOU_ATTR_PEER_V6] = NLA_POLICY_EXACT_LEN(16),
 	[FOU_ATTR_PEER_PORT] = { .type = NLA_BE16, },
 	[FOU_ATTR_IFINDEX] = { .type = NLA_S32, },
 };
-- 
2.50.1

On Mon,  1 Sep 2025 14:50:20 +0000 Asbjørn Sloth Tønnesen wrote:
> While fixing the binary min-len implementaion, I noticed that
> the only user, should AFAICT be using exact-len instead.
> 
> In net/ipv4/fou_core.c FOU_ATTR_LOCAL_V6 and FOU_ATTR_PEER_V6
> are only used for singular IPv6 addresses, a exact-len policy,
> therefore seams like a better fit.
> 
> AFAICT this was caused by lacking support for the exact-len check
> at the time of the blamed commit, which was later remedied by
> c63ad379526 ("tools: ynl-gen: add support for exact-len validation").

No, take a look at 1d562c32e43. The intention was to keep the code
before and after the same. I agree that the check is not ideal but
it's not really a bug to ignore some input. So if you want to clean
this up -- net-next and no Fixes tag..

> This patch therefore changes the local-v6/peer-v6 attributes to
> use an exact-len check, instead of a min-len check.