Merge branch 'netlink_ext_ACK'

Johannes Berg says:

====================
netlink extended ACK reporting

Changes since v4:
 * use __NLMSGERR_ATTR_MAX instead of NUM_NLMSGERR_ATTRS

Changes since v3:
 * Add NLM_F_CAPPED and NLM_F_ACK_TLVS flags, to allow entirely
   stateless parsing of the ACK messages by looking at the new
   flags. Need to check NLM_F_ACK_TLVS first, since capping can
   be done in kernels before this patchset without setting the
   flag.
 * Remove "missing_attr" functionality - this can obviously be
   added back rather easily, but I'd rather have more discussion
   about the nesting problem there.
 * Improve documentation of NLMSGERR_ATTR_OFFS
 * Improve message structure documentation, documenting that the
   request message is always capped for success cases
 * fix nlmsg_len of the outer message by calling nlmsg_end()
 * fix memcpy() of the request in success cases, going back to
   the original code that I'd changed before due to the payload
   adjustments that I reverted when introducing tlvlen

Changes since v2:
 * add NUM_NLMSGERR_ATTRS, NLMSGERR_ATTR_MAX
 * fix cookie length to 20 (sha-1 length)
 * move struct members for cookie to patch 3 where they should be
 * another cleanup suggested by David Ahern

Changes since v1:
 * credit Pablo and Jamal
 * incorporate suggestion from David Ahern
 * fix compilation in decnet
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

5 files changed, 112 insertions, 16 deletions

diff --git a/include/linux/netlink.h b/include/linux/netlink.h
index da14ab61f363..8d2a8924705c 100644
--- a/include/linux/netlink.h
+++ b/include/linux/netlink.h
@@ -62,11 +62,42 @@ netlink_kernel_create(struct net *net, int unit, struct netlink_kernel_cfg *cfg)
 	return __netlink_kernel_create(net, unit, THIS_MODULE, cfg);
 }
 
+/* this can be increased when necessary - don't expose to userland */
+#define NETLINK_MAX_COOKIE_LEN	20
+
+/**
+ * struct netlink_ext_ack - netlink extended ACK report struct
+ * @_msg: message string to report - don't access directly, use
+ *	%NL_SET_ERR_MSG
+ * @bad_attr: attribute with error
+ * @cookie: cookie data to return to userspace (for success)
+ * @cookie_len: actual cookie data length
+ */
+struct netlink_ext_ack {
+	const char *_msg;
+	const struct nlattr *bad_attr;
+	u8 cookie[NETLINK_MAX_COOKIE_LEN];
+	u8 cookie_len;
+};
+
+/* Always use this macro, this allows later putting the
+ * message into a separate section or such for things
+ * like translation or listing all possible messages.
+ * Currently string formatting is not supported (due
+ * to the lack of an output buffer.)
+ */
+#define NL_SET_ERR_MSG(extack, msg) do {	\
+	static const char _msg[] = (msg);	\
+						\
+	(extack)->_msg = _msg;			\
+} while (0)
+
 extern void netlink_kernel_release(struct sock *sk);
 extern int __netlink_change_ngroups(struct sock *sk, unsigned int groups);
 extern int netlink_change_ngroups(struct sock *sk, unsigned int groups);
 extern void __netlink_clear_multicast_users(struct sock *sk, unsigned int group);
-extern void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr *nlh, int err);
+extern void netlink_ack(struct sk_buff *in_skb, struct nlmsghdr *nlh, int err,
+			const struct netlink_ext_ack *extack);
 extern int netlink_has_listeners(struct sock *sk, unsigned int group);
 
 extern int netlink_unicast(struct sock *ssk, struct sk_buff *skb, __u32 portid, int nonblock);
diff --git a/include/net/genetlink.h b/include/net/genetlink.h
index a34275be3600..68b88192b00c 100644
--- a/include/net/genetlink.h
+++ b/include/net/genetlink.h
@@ -84,6 +84,7 @@ struct nlattr **genl_family_attrbuf(const struct genl_family *family);
  * @attrs: netlink attributes
  * @_net: network namespace
  * @user_ptr: user pointers
+ * @extack: extended ACK report struct
  */
 struct genl_info {
 	u32			snd_seq;
@@ -94,6 +95,7 @@ struct genl_info {
 	struct nlattr **	attrs;
 	possible_net_t		_net;
 	void *			user_ptr[2];
+	struct netlink_ext_ack *extack;
 };
 
 static inline struct net *genl_info_net(struct genl_info *info)
@@ -106,6 +108,16 @@ static inline void genl_info_net_set(struct genl_info *info, struct net *net)
 	write_pnet(&info->_net, net);
 }
 
+#define GENL_SET_ERR_MSG(info, msg) NL_SET_ERR_MSG((info)->extack, msg)
+
+static inline int genl_err_attr(struct genl_info *info, int err,
+				struct nlattr *attr)
+{
+	info->extack->bad_attr = attr;
+
+	return err;
+}
+
 /**
  * struct genl_ops - generic netlink operations
  * @cmd: command identifier
@@ -162,14 +174,16 @@ genlmsg_nlhdr(void *user_hdr, const struct genl_family *family)
  * @tb: destination array with maxtype+1 elements
  * @maxtype: maximum attribute type to be expected
  * @policy: validation policy
- * */
+ * @extack: extended ACK report struct
+ */
 static inline int genlmsg_parse(const struct nlmsghdr *nlh,
 				const struct genl_family *family,
 				struct nlattr *tb[], int maxtype,
-				const struct nla_policy *policy)
+				const struct nla_policy *policy,
+				struct netlink_ext_ack *extack)
 {
 	return nlmsg_parse(nlh, family->hdrsize + GENL_HDRLEN, tb, maxtype,
-			   policy);
+			   policy, extack);
 }
 
 /**
diff --git a/include/net/netlink.h b/include/net/netlink.h
index b239fcd33d80..01709172b3d3 100644
--- a/include/net/netlink.h
+++ b/include/net/netlink.h
@@ -233,14 +233,17 @@ struct nl_info {
 };
 
 int netlink_rcv_skb(struct sk_buff *skb,
-		    int (*cb)(struct sk_buff *, struct nlmsghdr *));
+		    int (*cb)(struct sk_buff *, struct nlmsghdr *,
+			      struct netlink_ext_ack *));
 int nlmsg_notify(struct sock *sk, struct sk_buff *skb, u32 portid,
 		 unsigned int group, int report, gfp_t flags);
 
 int nla_validate(const struct nlattr *head, int len, int maxtype,
-		 const struct nla_policy *policy);
+		 const struct nla_policy *policy,
+		 struct netlink_ext_ack *extack);
 int nla_parse(struct nlattr **tb, int maxtype, const struct nlattr *head,
-	      int len, const struct nla_policy *policy);
+	      int len, const struct nla_policy *policy,
+	      struct netlink_ext_ack *extack);
 int nla_policy_len(const struct nla_policy *, int);
 struct nlattr *nla_find(const struct nlattr *head, int len, int attrtype);
 size_t nla_strlcpy(char *dst, const struct nlattr *nla, size_t dstsize);
@@ -374,18 +377,20 @@ nlmsg_next(const struct nlmsghdr *nlh, int *remaining)
  * @tb: destination array with maxtype+1 elements
  * @maxtype: maximum attribute type to be expected
  * @policy: validation policy
+ * @extack: extended ACK report struct
  *
  * See nla_parse()
  */
 static inline int nlmsg_parse(const struct nlmsghdr *nlh, int hdrlen,
 			      struct nlattr *tb[], int maxtype,
-			      const struct nla_policy *policy)
+			      const struct nla_policy *policy,
+			      struct netlink_ext_ack *extack)
 {
 	if (nlh->nlmsg_len < nlmsg_msg_size(hdrlen))
 		return -EINVAL;
 
 	return nla_parse(tb, maxtype, nlmsg_attrdata(nlh, hdrlen),
-			 nlmsg_attrlen(nlh, hdrlen), policy);
+			 nlmsg_attrlen(nlh, hdrlen), policy, extack);
 }
 
 /**
@@ -409,16 +414,19 @@ static inline struct nlattr *nlmsg_find_attr(const struct nlmsghdr *nlh,
  * @hdrlen: length of familiy specific header
  * @maxtype: maximum attribute type to be expected
  * @policy: validation policy
+ * @extack: extended ACK report struct
  */
 static inline int nlmsg_validate(const struct nlmsghdr *nlh,
 				 int hdrlen, int maxtype,
-				 const struct nla_policy *policy)
+				 const struct nla_policy *policy,
+				 struct netlink_ext_ack *extack)
 {
 	if (nlh->nlmsg_len < nlmsg_msg_size(hdrlen))
 		return -EINVAL;
 
 	return nla_validate(nlmsg_attrdata(nlh, hdrlen),
-			    nlmsg_attrlen(nlh, hdrlen), maxtype, policy);
+			    nlmsg_attrlen(nlh, hdrlen), maxtype, policy,
+			    extack);
 }
 
 /**
@@ -739,14 +747,17 @@ nla_find_nested(const struct nlattr *nla, int attrtype)
  * @maxtype: maximum attribute type to be expected
  * @nla: attribute containing the nested attributes
  * @policy: validation policy
+ * @extack: extended ACK report struct
  *
  * See nla_parse()
  */
 static inline int nla_parse_nested(struct nlattr *tb[], int maxtype,
 				   const struct nlattr *nla,
-				   const struct nla_policy *policy)
+				   const struct nla_policy *policy,
+				   struct netlink_ext_ack *extack)
 {
-	return nla_parse(tb, maxtype, nla_data(nla), nla_len(nla), policy);
+	return nla_parse(tb, maxtype, nla_data(nla), nla_len(nla), policy,
+			 extack);
 }
 
 /**
@@ -1252,6 +1263,7 @@ static inline void nla_nest_cancel(struct sk_buff *skb, struct nlattr *start)
  * @start: container attribute
  * @maxtype: maximum attribute type to be expected
  * @policy: validation policy
+ * @extack: extended ACK report struct
  *
  * Validates all attributes in the nested attribute stream against the
  * specified policy. Attributes with a type exceeding maxtype will be
@@ -1260,9 +1272,11 @@ static inline void nla_nest_cancel(struct sk_buff *skb, struct nlattr *start)
  * Returns 0 on success or a negative error code.
  */
 static inline int nla_validate_nested(const struct nlattr *start, int maxtype,
-				      const struct nla_policy *policy)
+				      const struct nla_policy *policy,
+				      struct netlink_ext_ack *extack)
 {
-	return nla_validate(nla_data(start), nla_len(start), maxtype, policy);
+	return nla_validate(nla_data(start), nla_len(start), maxtype, policy,
+			    extack);
 }
 
 /**
diff --git a/include/net/rtnetlink.h b/include/net/rtnetlink.h
index 106de5f7bf06..c07b941fce89 100644
--- a/include/net/rtnetlink.h
+++ b/include/net/rtnetlink.h
@@ -158,7 +158,8 @@ struct net_device *rtnl_create_link(struct net *net, const char *ifname,
 int rtnl_delete_link(struct net_device *dev);
 int rtnl_configure_link(struct net_device *dev, const struct ifinfomsg *ifm);
 
-int rtnl_nla_parse_ifla(struct nlattr **tb, const struct nlattr *head, int len);
+int rtnl_nla_parse_ifla(struct nlattr **tb, const struct nlattr *head, int len,
+			struct netlink_ext_ack *exterr);
 
 #define MODULE_ALIAS_RTNL_LINK(kind) MODULE_ALIAS("rtnl-link-" kind)
 
diff --git a/include/uapi/linux/netlink.h b/include/uapi/linux/netlink.h
index b2c9c26ea30f..f86127a46cfc 100644
--- a/include/uapi/linux/netlink.h
+++ b/include/uapi/linux/netlink.h
@@ -69,6 +69,10 @@ struct nlmsghdr {
 #define NLM_F_CREATE	0x400	/* Create, if it does not exist	*/
 #define NLM_F_APPEND	0x800	/* Add to end of list		*/
 
+/* Flags for ACK message */
+#define NLM_F_CAPPED	0x100	/* request was capped */
+#define NLM_F_ACK_TLVS	0x200	/* extended ACK TVLs were included */
+
 /*
    4.4BSD ADD		NLM_F_CREATE|NLM_F_EXCL
    4.4BSD CHANGE	NLM_F_REPLACE
@@ -101,6 +105,37 @@ struct nlmsghdr {
 struct nlmsgerr {
 	int		error;
 	struct nlmsghdr msg;
+	/*
+	 * followed by the message contents unless NETLINK_CAP_ACK was set
+	 * or the ACK indicates success (error == 0)
+	 * message length is aligned with NLMSG_ALIGN()
+	 */
+	/*
+	 * followed by TLVs defined in enum nlmsgerr_attrs
+	 * if NETLINK_EXT_ACK was set
+	 */
+};
+
+/**
+ * enum nlmsgerr_attrs - nlmsgerr attributes
+ * @NLMSGERR_ATTR_UNUSED: unused
+ * @NLMSGERR_ATTR_MSG: error message string (string)
+ * @NLMSGERR_ATTR_OFFS: offset of the invalid attribute in the original
+ *	 message, counting from the beginning of the header (u32)
+ * @NLMSGERR_ATTR_COOKIE: arbitrary subsystem specific cookie to
+ *	be used - in the success case - to identify a created
+ *	object or operation or similar (binary)
+ * @__NLMSGERR_ATTR_MAX: number of attributes
+ * @NLMSGERR_ATTR_MAX: highest attribute number
+ */
+enum nlmsgerr_attrs {
+	NLMSGERR_ATTR_UNUSED,
+	NLMSGERR_ATTR_MSG,
+	NLMSGERR_ATTR_OFFS,
+	NLMSGERR_ATTR_COOKIE,
+
+	__NLMSGERR_ATTR_MAX,
+	NLMSGERR_ATTR_MAX = __NLMSGERR_ATTR_MAX - 1
 };
 
 #define NETLINK_ADD_MEMBERSHIP		1
@@ -115,6 +150,7 @@ struct nlmsgerr {
 #define NETLINK_LISTEN_ALL_NSID		8
 #define NETLINK_LIST_MEMBERSHIPS	9
 #define NETLINK_CAP_ACK			10
+#define NETLINK_EXT_ACK			11
 
 struct nl_pktinfo {
 	__u32	group;