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>
---
 tools/net/ynl/lib/ynl-priv.h     | 10 +++++++++-
 tools/net/ynl/lib/ynl.c          |  6 +++---
 tools/net/ynl/pyynl/ynl_gen_c.py |  2 +-
 3 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/tools/net/ynl/lib/ynl-priv.h b/tools/net/ynl/lib/ynl-priv.h
index 824777d7e05e..29481989ea76 100644
--- a/tools/net/ynl/lib/ynl-priv.h
+++ b/tools/net/ynl/lib/ynl-priv.h
@@ -106,7 +106,6 @@ ynl_gemsg_start_req(struct ynl_sock *ys, __u32 id, __u8 cmd, __u8 version);
 struct nlmsghdr *
 ynl_gemsg_start_dump(struct ynl_sock *ys, __u32 id, __u8 cmd, __u8 version);
 
-int ynl_attr_validate(struct ynl_parse_arg *yarg, const struct nlattr *attr);
 int ynl_submsg_failed(struct ynl_parse_arg *yarg, const char *field_name,
 		      const char *sel_name);
 
@@ -467,4 +466,13 @@ ynl_attr_put_sint(struct nlmsghdr *nlh, __u16 type, __s64 data)
 	else
 		ynl_attr_put_s64(nlh, type, data);
 }
+
+int __ynl_attr_validate(struct ynl_parse_arg *yarg, const struct nlattr *attr,
+			unsigned int type);
+
+static inline int ynl_attr_validate(struct ynl_parse_arg *yarg,
+				    const struct nlattr *attr)
+{
+	return __ynl_attr_validate(yarg, attr, ynl_attr_type(attr));
+}
 #endif
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");
diff --git a/tools/net/ynl/pyynl/ynl_gen_c.py b/tools/net/ynl/pyynl/ynl_gen_c.py
index 9555c9a2fea5..8f8d33593326 100755
--- a/tools/net/ynl/pyynl/ynl_gen_c.py
+++ b/tools/net/ynl/pyynl/ynl_gen_c.py
@@ -830,7 +830,7 @@ class TypeArrayNest(Type):
         local_vars = ['const struct nlattr *attr2;']
         get_lines = [f'attr_{self.c_name} = attr;',
                      'ynl_attr_for_each_nested(attr2, attr) {',
-                     '\tif (ynl_attr_validate(yarg, attr2))',
+                     '\tif (__ynl_attr_validate(yarg, attr2, type))',
                      '\t\treturn YNL_PARSE_CB_ERROR;',
                      f'\tn_{self.c_name}++;',
                      '}']
-- 
2.51.0