Merge branch 'netlink-support-reporting-missing-attributes'

Jakub Kicinski says:

====================
netlink: support reporting missing attributes

This series adds support for reporting missing attributes
in a structured way. We communicate the type of the missing
attribute and if it was missing inside a nest the offset
of that nest.

Example of (YAML-based) user space reporting ethtool header
missing:

 Kernel error: missing attribute: .header

I was tempted to integrate the check with the policy
but it seems tricky without doing a full scan, and there
may be a ton of attrs in the policy. So leaving that
for later.
====================

Link: https://lore.kernel.org/r/20220826030935.2165661-1-kuba@kernel.org
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

8 files changed, 133 insertions, 54 deletions

diff --git a/Documentation/userspace-api/netlink/intro.rst b/Documentation/userspace-api/netlink/intro.rst
index 94337f79e077..8f1220756412 100644
--- a/Documentation/userspace-api/netlink/intro.rst
+++ b/Documentation/userspace-api/netlink/intro.rst
@@ -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.
 
diff --git a/include/linux/netlink.h b/include/linux/netlink.h
index bda1c385cffb..d51e041d2242 100644
--- a/include/linux/netlink.h
+++ b/include/linux/netlink.h
@@ -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 +130,26 @@ 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)
+
+#define NL_REQ_ATTR_CHECK(extack, nest, tb, type) ({		\
+	struct nlattr **__tb = (tb);				\
+	u32 __attr = (type);					\
+	int __retval;						\
+								\
+	__retval = !__tb[__attr];				\
+	if (__retval)						\
+		NL_SET_ERR_ATTR_MISS((extack), (nest), __attr);	\
+	__retval;						\
+})
+
 static inline void nl_set_extack_cookie_u64(struct netlink_ext_ack *extack,
 					    u64 cookie)
 {
diff --git a/include/net/genetlink.h b/include/net/genetlink.h
index a4827b5e1e07..8f780170e2f8 100644
--- a/include/net/genetlink.h
+++ b/include/net/genetlink.h
@@ -110,6 +110,13 @@ static inline void genl_info_net_set(struct genl_info *info, struct net *net)
 
 #define GENL_SET_ERR_MSG(info, msg) NL_SET_ERR_MSG((info)->extack, msg)
 
+/* Report that a root attribute is missing */
+#define GENL_REQ_ATTR_CHECK(info, attr) ({				\
+	struct genl_info *__info = (info);				\
+									\
+	NL_REQ_ATTR_CHECK(__info->extack, NULL, __info->attrs, (attr)); \
+})
+
 enum genl_validate_flags {
 	GENL_DONT_VALIDATE_STRICT		= BIT(0),
 	GENL_DONT_VALIDATE_DUMP			= BIT(1),
diff --git a/include/uapi/linux/netlink.h b/include/uapi/linux/netlink.h
index e0ab261ceca2..e0689dbd2cde 100644
--- a/include/uapi/linux/netlink.h
+++ b/include/uapi/linux/netlink.h
@@ -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
diff --git a/net/core/devlink.c b/net/core/devlink.c
index 3396fdf802b6..95fd20ef5862 100644
--- a/net/core/devlink.c
+++ b/net/core/devlink.c
@@ -1710,7 +1710,7 @@ static int devlink_nl_cmd_port_split_doit(struct sk_buff *skb,
 	struct devlink *devlink = info->user_ptr[0];
 	u32 count;
 
-	if (!info->attrs[DEVLINK_ATTR_PORT_SPLIT_COUNT])
+	if (GENL_REQ_ATTR_CHECK(info, DEVLINK_ATTR_PORT_SPLIT_COUNT))
 		return -EINVAL;
 	if (!devlink->ops->port_split)
 		return -EOPNOTSUPP;
@@ -1838,7 +1838,7 @@ static int devlink_nl_cmd_port_del_doit(struct sk_buff *skb,
 	if (!devlink->ops->port_del)
 		return -EOPNOTSUPP;
 
-	if (!info->attrs[DEVLINK_ATTR_PORT_INDEX]) {
+	if (GENL_REQ_ATTR_CHECK(info, DEVLINK_ATTR_PORT_INDEX)) {
 		NL_SET_ERR_MSG_MOD(extack, "Port index is not specified");
 		return -EINVAL;
 	}
@@ -2690,7 +2690,7 @@ static int devlink_nl_cmd_sb_pool_set_doit(struct sk_buff *skb,
 	if (err)
 		return err;
 
-	if (!info->attrs[DEVLINK_ATTR_SB_POOL_SIZE])
+	if (GENL_REQ_ATTR_CHECK(info, DEVLINK_ATTR_SB_POOL_SIZE))
 		return -EINVAL;
 
 	size = nla_get_u32(info->attrs[DEVLINK_ATTR_SB_POOL_SIZE]);
@@ -2900,7 +2900,7 @@ static int devlink_nl_cmd_sb_port_pool_set_doit(struct sk_buff *skb,
 	if (err)
 		return err;
 
-	if (!info->attrs[DEVLINK_ATTR_SB_THRESHOLD])
+	if (GENL_REQ_ATTR_CHECK(info, DEVLINK_ATTR_SB_THRESHOLD))
 		return -EINVAL;
 
 	threshold = nla_get_u32(info->attrs[DEVLINK_ATTR_SB_THRESHOLD]);
@@ -3156,7 +3156,7 @@ static int devlink_nl_cmd_sb_tc_pool_bind_set_doit(struct sk_buff *skb,
 	if (err)
 		return err;
 
-	if (!info->attrs[DEVLINK_ATTR_SB_THRESHOLD])
+	if (GENL_REQ_ATTR_CHECK(info, DEVLINK_ATTR_SB_THRESHOLD))
 		return -EINVAL;
 
 	threshold = nla_get_u32(info->attrs[DEVLINK_ATTR_SB_THRESHOLD]);
@@ -3845,7 +3845,7 @@ static int devlink_nl_cmd_dpipe_entries_get(struct sk_buff *skb,
 	struct devlink_dpipe_table *table;
 	const char *table_name;
 
-	if (!info->attrs[DEVLINK_ATTR_DPIPE_TABLE_NAME])
+	if (GENL_REQ_ATTR_CHECK(info, DEVLINK_ATTR_DPIPE_TABLE_NAME))
 		return -EINVAL;
 
 	table_name = nla_data(info->attrs[DEVLINK_ATTR_DPIPE_TABLE_NAME]);
@@ -4029,8 +4029,9 @@ static int devlink_nl_cmd_dpipe_table_counters_set(struct sk_buff *skb,
 	const char *table_name;
 	bool counters_enable;
 
-	if (!info->attrs[DEVLINK_ATTR_DPIPE_TABLE_NAME] ||
-	    !info->attrs[DEVLINK_ATTR_DPIPE_TABLE_COUNTERS_ENABLED])
+	if (GENL_REQ_ATTR_CHECK(info, DEVLINK_ATTR_DPIPE_TABLE_NAME) ||
+	    GENL_REQ_ATTR_CHECK(info,
+				DEVLINK_ATTR_DPIPE_TABLE_COUNTERS_ENABLED))
 		return -EINVAL;
 
 	table_name = nla_data(info->attrs[DEVLINK_ATTR_DPIPE_TABLE_NAME]);
@@ -4119,8 +4120,8 @@ static int devlink_nl_cmd_resource_set(struct sk_buff *skb,
 	u64 size;
 	int err;
 
-	if (!info->attrs[DEVLINK_ATTR_RESOURCE_ID] ||
-	    !info->attrs[DEVLINK_ATTR_RESOURCE_SIZE])
+	if (GENL_REQ_ATTR_CHECK(info, DEVLINK_ATTR_RESOURCE_ID) ||
+	    GENL_REQ_ATTR_CHECK(info, DEVLINK_ATTR_RESOURCE_SIZE))
 		return -EINVAL;
 	resource_id = nla_get_u64(info->attrs[DEVLINK_ATTR_RESOURCE_ID]);
 
@@ -4821,7 +4822,7 @@ static int devlink_nl_cmd_flash_update(struct sk_buff *skb,
 	if (!devlink->ops->flash_update)
 		return -EOPNOTSUPP;
 
-	if (!info->attrs[DEVLINK_ATTR_FLASH_UPDATE_FILE_NAME])
+	if (GENL_REQ_ATTR_CHECK(info, DEVLINK_ATTR_FLASH_UPDATE_FILE_NAME))
 		return -EINVAL;
 
 	ret = devlink_flash_component_get(devlink,
@@ -4998,10 +4999,8 @@ static int devlink_nl_cmd_selftests_run(struct sk_buff *skb,
 	if (!devlink->ops->selftest_run || !devlink->ops->selftest_check)
 		return -EOPNOTSUPP;
 
-	if (!info->attrs[DEVLINK_ATTR_SELFTESTS]) {
-		NL_SET_ERR_MSG_MOD(info->extack, "selftest required");
+	if (GENL_REQ_ATTR_CHECK(info, DEVLINK_ATTR_SELFTESTS))
 		return -EINVAL;
-	}
 
 	attrs = info->attrs[DEVLINK_ATTR_SELFTESTS];
 
@@ -5455,7 +5454,7 @@ static int
 devlink_param_type_get_from_info(struct genl_info *info,
 				 enum devlink_param_type *param_type)
 {
-	if (!info->attrs[DEVLINK_ATTR_PARAM_TYPE])
+	if (GENL_REQ_ATTR_CHECK(info, DEVLINK_ATTR_PARAM_TYPE))
 		return -EINVAL;
 
 	switch (nla_get_u8(info->attrs[DEVLINK_ATTR_PARAM_TYPE])) {
@@ -5532,7 +5531,7 @@ devlink_param_get_from_info(struct list_head *param_list,
 {
 	char *param_name;
 
-	if (!info->attrs[DEVLINK_ATTR_PARAM_NAME])
+	if (GENL_REQ_ATTR_CHECK(info, DEVLINK_ATTR_PARAM_NAME))
 		return NULL;
 
 	param_name = nla_data(info->attrs[DEVLINK_ATTR_PARAM_NAME]);
@@ -5598,7 +5597,7 @@ static int __devlink_nl_cmd_param_set_doit(struct devlink *devlink,
 			return err;
 	}
 
-	if (!info->attrs[DEVLINK_ATTR_PARAM_VALUE_CMODE])
+	if (GENL_REQ_ATTR_CHECK(info, DEVLINK_ATTR_PARAM_VALUE_CMODE))
 		return -EINVAL;
 	cmode = nla_get_u8(info->attrs[DEVLINK_ATTR_PARAM_VALUE_CMODE]);
 	if (!devlink_param_cmode_is_supported(param, cmode))
@@ -6118,7 +6117,7 @@ static int devlink_nl_cmd_region_get_doit(struct sk_buff *skb,
 	unsigned int index;
 	int err;
 
-	if (!info->attrs[DEVLINK_ATTR_REGION_NAME])
+	if (GENL_REQ_ATTR_CHECK(info, DEVLINK_ATTR_REGION_NAME))
 		return -EINVAL;
 
 	if (info->attrs[DEVLINK_ATTR_PORT_INDEX]) {
@@ -6251,8 +6250,8 @@ static int devlink_nl_cmd_region_del(struct sk_buff *skb,
 	unsigned int index;
 	u32 snapshot_id;
 
-	if (!info->attrs[DEVLINK_ATTR_REGION_NAME] ||
-	    !info->attrs[DEVLINK_ATTR_REGION_SNAPSHOT_ID])
+	if (GENL_REQ_ATTR_CHECK(info, DEVLINK_ATTR_REGION_NAME) ||
+	    GENL_REQ_ATTR_CHECK(info, DEVLINK_ATTR_REGION_SNAPSHOT_ID))
 		return -EINVAL;
 
 	region_name = nla_data(info->attrs[DEVLINK_ATTR_REGION_NAME]);
@@ -6300,7 +6299,7 @@ devlink_nl_cmd_region_new(struct sk_buff *skb, struct genl_info *info)
 	u8 *data;
 	int err;
 
-	if (!info->attrs[DEVLINK_ATTR_REGION_NAME]) {
+	if (GENL_REQ_ATTR_CHECK(info, DEVLINK_ATTR_REGION_NAME)) {
 		NL_SET_ERR_MSG_MOD(info->extack, "No region name provided");
 		return -EINVAL;
 	}
diff --git a/net/ethtool/netlink.c b/net/ethtool/netlink.c
index d5e77f1cbbfa..f4e41a6e0163 100644
--- a/net/ethtool/netlink.c
+++ b/net/ethtool/netlink.c
@@ -361,6 +361,9 @@ static int ethnl_default_doit(struct sk_buff *skb, struct genl_info *info)
 	ops = ethnl_default_requests[cmd];
 	if (WARN_ONCE(!ops, "cmd %u has no ethnl_request_ops\n", cmd))
 		return -EOPNOTSUPP;
+	if (GENL_REQ_ATTR_CHECK(info, ops->hdr_attr))
+		return -EINVAL;
+
 	req_info = kzalloc(ops->req_info_size, GFP_KERNEL);
 	if (!req_info)
 		return -ENOMEM;
diff --git a/net/ethtool/strset.c b/net/ethtool/strset.c
index 2d51b7ab4dc5..3f7de54d85fb 100644
--- a/net/ethtool/strset.c
+++ b/net/ethtool/strset.c
@@ -167,7 +167,7 @@ static int strset_get_id(const struct nlattr *nest, u32 *val,
 			       get_stringset_policy, extack);
 	if (ret < 0)
 		return ret;
-	if (!tb[ETHTOOL_A_STRINGSET_ID])
+	if (NL_REQ_ATTR_CHECK(extack, nest, tb, ETHTOOL_A_STRINGSET_ID))
 		return -EINVAL;
 
 	*val = nla_get_u32(tb[ETHTOOL_A_STRINGSET_ID]);
diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
index 0cd91f813a3b..f89ba302ac6e 100644
--- a/net/netlink/af_netlink.c
+++ b/net/netlink/af_netlink.c
@@ -2400,6 +2400,69 @@ error_free:
 }
 EXPORT_SYMBOL(__netlink_dump_start);
 
+static size_t
+netlink_ack_tlv_len(struct netlink_sock *nlk, int err,
+		    const struct netlink_ext_ack *extack)
+{
+	size_t tlvlen;
+
+	if (!extack || !(nlk->flags & NETLINK_F_EXT_ACK))
+		return 0;
+
+	tlvlen = 0;
+	if (extack->_msg)
+		tlvlen += nla_total_size(strlen(extack->_msg) + 1);
+	if (extack->cookie_len)
+		tlvlen += nla_total_size(extack->cookie_len);
+
+	/* Following attributes are only reported as error (not warning) */
+	if (!err)
+		return tlvlen;
+
+	if (extack->bad_attr)
+		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;
+}
+
+static void
+netlink_ack_tlv_fill(struct sk_buff *in_skb, struct sk_buff *skb,
+		     struct nlmsghdr *nlh, int err,
+		     const struct netlink_ext_ack *extack)
+{
+	if (extack->_msg)
+		WARN_ON(nla_put_string(skb, NLMSGERR_ATTR_MSG, extack->_msg));
+	if (extack->cookie_len)
+		WARN_ON(nla_put(skb, NLMSGERR_ATTR_COOKIE,
+				extack->cookie_len, extack->cookie));
+
+	if (!err)
+		return;
+
+	if (extack->bad_attr &&
+	    !WARN_ON((u8 *)extack->bad_attr < in_skb->data ||
+		     (u8 *)extack->bad_attr >= in_skb->data + in_skb->len))
+		WARN_ON(nla_put_u32(skb, NLMSGERR_ATTR_OFFS,
+				    (u8 *)extack->bad_attr - (u8 *)nlh));
+	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,
 		 const struct netlink_ext_ack *extack)
 {
@@ -2407,29 +2470,20 @@ void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr *nlh, int err,
 	struct nlmsghdr *rep;
 	struct nlmsgerr *errmsg;
 	size_t payload = sizeof(*errmsg);
-	size_t tlvlen = 0;
 	struct netlink_sock *nlk = nlk_sk(NETLINK_CB(in_skb).sk);
 	unsigned int flags = 0;
-	bool nlk_has_extack = nlk->flags & NETLINK_F_EXT_ACK;
+	size_t tlvlen;
 
 	/* Error messages get the original request appened, unless the user
 	 * requests to cap the error message, and get extra error data if
 	 * requested.
 	 */
-	if (nlk_has_extack && extack && extack->_msg)
-		tlvlen += nla_total_size(strlen(extack->_msg) + 1);
-
 	if (err && !(nlk->flags & NETLINK_F_CAP_ACK))
 		payload += nlmsg_len(nlh);
 	else
 		flags |= NLM_F_CAPPED;
-	if (err && nlk_has_extack && extack && extack->bad_attr)
-		tlvlen += nla_total_size(sizeof(u32));
-	if (nlk_has_extack && extack && extack->cookie_len)
-		tlvlen += nla_total_size(extack->cookie_len);
-	if (err && nlk_has_extack && extack && extack->policy)
-		tlvlen += netlink_policy_dump_attr_size_estimate(extack->policy);
 
+	tlvlen = netlink_ack_tlv_len(nlk, err, extack);
 	if (tlvlen)
 		flags |= NLM_F_ACK_TLVS;
 
@@ -2446,25 +2500,8 @@ void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr *nlh, int err,
 	errmsg->error = err;
 	memcpy(&errmsg->msg, nlh, payload > sizeof(*errmsg) ? nlh->nlmsg_len : sizeof(*nlh));
 
-	if (nlk_has_extack && extack) {
-		if (extack->_msg) {
-			WARN_ON(nla_put_string(skb, NLMSGERR_ATTR_MSG,
-					       extack->_msg));
-		}
-		if (err && extack->bad_attr &&
-		    !WARN_ON((u8 *)extack->bad_attr < in_skb->data ||
-			     (u8 *)extack->bad_attr >= in_skb->data +
-						       in_skb->len))
-			WARN_ON(nla_put_u32(skb, NLMSGERR_ATTR_OFFS,
-					    (u8 *)extack->bad_attr -
-					    (u8 *)nlh));
-		if (extack->cookie_len)
-			WARN_ON(nla_put(skb, NLMSGERR_ATTR_COOKIE,
-					extack->cookie_len, extack->cookie));
-		if (extack->policy)
-			netlink_policy_dump_write_attr(skb, extack->policy,
-						       NLMSGERR_ATTR_POLICY);
-	}
+	if (tlvlen)
+		netlink_ack_tlv_fill(in_skb, skb, nlh, err, extack);
 
 	nlmsg_end(skb, rep);