tools: ynl-gen: validate nested arrays

In nested arrays don't require that the intermediate attribute
type should be a valid attribute type, it might just be zero
or an incrementing index, it is often not even used.

See include/net/netlink.h about NLA_NESTED_ARRAY:
> The difference to NLA_NESTED is the structure:
> NLA_NESTED has the nested attributes directly inside
> while an array has the nested attributes at another
> level down and the attribute types directly in the
> nesting don't matter.

Example based on include/uapi/linux/wireguard.h:
 > WGDEVICE_A_PEERS: NLA_NESTED
 >   0: NLA_NESTED
 >     WGPEER_A_PUBLIC_KEY: NLA_EXACT_LEN, len WG_KEY_LEN
 >     [..]
 >   0: NLA_NESTED
 >     ...
 >   ...

Previous the check required that the nested type was valid
in the parent attribute set, which in this case resolves to
WGDEVICE_A_UNSPEC, which is YNL_PT_REJECT, and it took the
early exit and returned YNL_PARSE_CB_ERROR.

This patch renames the old nl_attr_validate() to
__nl_attr_validate(), and creates a new inline function
nl_attr_validate() to mimic the old one.

The new __nl_attr_validate() takes the attribute type as an
argument, so we can use it to validate attributes of a
nested attribute, in the context of the parents attribute
type, which in the above case is generated as:
[WGDEVICE_A_PEERS] = {
  .name = "peers",
  .type = YNL_PT_NEST,
  .nest = &wireguard_wgpeer_nest,
},

__nl_attr_validate() only checks if the attribute length
is plausible for a given attribute type, so the .nest in
the above example is not used.

As the new inline function needs to be defined after
ynl_attr_type(), then the definitions are moved down,
so we avoid a forward declaration of ynl_attr_type().

Some other examples are NL80211_BAND_ATTR_FREQS (nest) and
NL80211_ATTR_SUPPORTED_COMMANDS (u32) both in nl80211-user.c
$ make -C tools/net/ynl/generated nl80211-user.c

Signed-off-by: Asbjørn Sloth Tønnesen <ast@fiberby.net>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Link: https://patch.msgid.link/20250915144301.725949-7-ast@fiberby.net
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

1 files changed, 3 insertions, 3 deletions

diff --git a/tools/net/ynl/lib/ynl.c b/tools/net/ynl/lib/ynl.c
index 2a169c3c0797..2bcd781111d7 100644
--- a/tools/net/ynl/lib/ynl.c
+++ b/tools/net/ynl/lib/ynl.c
@@ -360,15 +360,15 @@ static int ynl_cb_done(const struct nlmsghdr *nlh, struct ynl_parse_arg *yarg)
 
 /* Attribute validation */
 
-int ynl_attr_validate(struct ynl_parse_arg *yarg, const struct nlattr *attr)
+int __ynl_attr_validate(struct ynl_parse_arg *yarg, const struct nlattr *attr,
+			unsigned int type)
 {
 	const struct ynl_policy_attr *policy;
-	unsigned int type, len;
 	unsigned char *data;
+	unsigned int len;
 
 	data = ynl_attr_data(attr);
 	len = ynl_attr_data_len(attr);
-	type = ynl_attr_type(attr);
 	if (type > yarg->rsp_policy->max_attr) {
 		yerr(yarg->ys, YNL_ERROR_INTERNAL,
 		     "Internal error, validating unknown attribute");