Commit 690252f1 authored by Jakub Kicinski's avatar Jakub Kicinski Committed by Paolo Abeni
Browse files

netlink: add support for ext_ack missing attributes 



There is currently no way to report via extack in a structured way
that an attribute is missing. This leads to families resorting to
string messages.

Add a pair of attributes - @offset and @type for machine-readable
way of reporting missing attributes. The @offset points to the
nest which should have contained the attribute, @type is the
expected nla_type. The offset will be skipped if the attribute
is missing at the message level rather than inside a nest.

User space should be able to figure out which attribute enum
(AKA attribute space AKA attribute set) the nest pointed to by
@offset is using.

Reviewed-by: default avatarJohannes Berg <johannes@sipsolutions.net>
Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
Signed-off-by: default avatarPaolo Abeni <pabeni@redhat.com>
parent 0c95cea2

Documentation/userspace-api/netlink/intro.rst

+5 −2
Original line number Diff line number Diff line
@@ -359,8 +359,8 @@ compatibility this feature has to be explicitly enabled by setting 
the ``NETLINK_EXT_ACK`` setsockopt() to ``1``.



Types of extended ack attributes are defined in enum nlmsgerr_attrs.

The two most commonly used attributes are ``NLMSGERR_ATTR_MSG``

and ``NLMSGERR_ATTR_OFFS``.

The most commonly used attributes are ``NLMSGERR_ATTR_MSG``,

``NLMSGERR_ATTR_OFFS`` and ``NLMSGERR_ATTR_MISS_*``.



``NLMSGERR_ATTR_MSG`` carries a message in English describing

the encountered problem. These messages are far more detailed
@@ -368,6 +368,9 @@ than what can be expressed thru standard UNIX error codes. 


``NLMSGERR_ATTR_OFFS`` points to the attribute which caused the problem.



``NLMSGERR_ATTR_MISS_TYPE`` and ``NLMSGERR_ATTR_MISS_NEST``

inform about a missing attribute.



Extended ACKs can be reported on errors as well as in case of success.

The latter should be treated as a warning.

include/linux/netlink.h

+13 −0
Original line number Diff line number Diff line
@@ -71,6 +71,8 @@ netlink_kernel_create(struct net *net, int unit, struct netlink_kernel_cfg *cfg) 
 *	%NL_SET_ERR_MSG

 * @bad_attr: attribute with error

 * @policy: policy for a bad attribute

 * @miss_type: attribute type which was missing

 * @miss_nest: nest missing an attribute (%NULL if missing top level attr)

 * @cookie: cookie data to return to userspace (for success)

 * @cookie_len: actual cookie data length

 */
@@ -78,6 +80,8 @@ struct netlink_ext_ack { 
	const char *_msg;

	const struct nlattr *bad_attr;

	const struct nla_policy *policy;

	const struct nlattr *miss_nest;

	u16 miss_type;

	u8 cookie[NETLINK_MAX_COOKIE_LEN];

	u8 cookie_len;

};
@@ -126,6 +130,15 @@ struct netlink_ext_ack { 
#define NL_SET_ERR_MSG_ATTR(extack, attr, msg)		\

	NL_SET_ERR_MSG_ATTR_POL(extack, attr, NULL, msg)



#define NL_SET_ERR_ATTR_MISS(extack, nest, type)  do {	\

	struct netlink_ext_ack *__extack = (extack);	\

							\

	if (__extack) {					\

		__extack->miss_nest = (nest);		\

		__extack->miss_type = (type);		\

	}						\

} while (0)



static inline void nl_set_extack_cookie_u64(struct netlink_ext_ack *extack,

					    u64 cookie)

{

include/uapi/linux/netlink.h

+6 −0
Original line number Diff line number Diff line
@@ -140,6 +140,10 @@ struct nlmsgerr { 
 *	be used - in the success case - to identify a created

 *	object or operation or similar (binary)

 * @NLMSGERR_ATTR_POLICY: policy for a rejected attribute

 * @NLMSGERR_ATTR_MISS_TYPE: type of a missing required attribute,

 *	%NLMSGERR_ATTR_MISS_NEST will not be present if the attribute was

 *	missing at the message level

 * @NLMSGERR_ATTR_MISS_NEST: offset of the nest where attribute was missing

 * @__NLMSGERR_ATTR_MAX: number of attributes

 * @NLMSGERR_ATTR_MAX: highest attribute number

 */
@@ -149,6 +153,8 @@ enum nlmsgerr_attrs { 
	NLMSGERR_ATTR_OFFS,

	NLMSGERR_ATTR_COOKIE,

	NLMSGERR_ATTR_POLICY,

	NLMSGERR_ATTR_MISS_TYPE,

	NLMSGERR_ATTR_MISS_NEST,



	__NLMSGERR_ATTR_MAX,

	NLMSGERR_ATTR_MAX = __NLMSGERR_ATTR_MAX - 1

net/netlink/af_netlink.c

+12 −0
Original line number Diff line number Diff line
@@ -2423,6 +2423,10 @@ netlink_ack_tlv_len(struct netlink_sock *nlk, int err, 
		tlvlen += nla_total_size(sizeof(u32));

	if (extack->policy)

		tlvlen += netlink_policy_dump_attr_size_estimate(extack->policy);

	if (extack->miss_type)

		tlvlen += nla_total_size(sizeof(u32));

	if (extack->miss_nest)

		tlvlen += nla_total_size(sizeof(u32));



	return tlvlen;

}
@@ -2449,6 +2453,14 @@ netlink_ack_tlv_fill(struct sk_buff *in_skb, struct sk_buff *skb, 
	if (extack->policy)

		netlink_policy_dump_write_attr(skb, extack->policy,

					       NLMSGERR_ATTR_POLICY);

	if (extack->miss_type)

		WARN_ON(nla_put_u32(skb, NLMSGERR_ATTR_MISS_TYPE,

				    extack->miss_type));

	if (extack->miss_nest &&

	    !WARN_ON((u8 *)extack->miss_nest < in_skb->data ||

		     (u8 *)extack->miss_nest > in_skb->data + in_skb->len))

		WARN_ON(nla_put_u32(skb, NLMSGERR_ATTR_MISS_NEST,

				    (u8 *)extack->miss_nest - (u8 *)nlh));

}



void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr *nlh, int err,