Merge branch 'genetlink-per-op-type-policies'

Jakub Kicinski says:

====================
genetlink: support per op type policies

While writing new genetlink families I was increasingly annoyed by the fact
that we don't support different policies for do and dump callbacks.
This makes it hard to do proper input validation for dumps which usually
have a lot more narrow range of accepted attributes.

There is also a minor inconvenience of not supporting different per_doit
and post_doit callbacks per op.

This series addresses those problems by introducing another op format.

v3:
 - minor fixes to patch 12 after I took it for a spin with a real family
 - adjust commit msg in patch 8
v2: https://lore.kernel.org/all/20221102213338.194672-1-kuba@kernel.org/
 - wait for net changes to propagate
 - restore the missing comment in patch 1
 - drop extra space in patch 3
 - improve commit message in patch 4
v1: https://lore.kernel.org/all/20221018230728.1039524-1-kuba@kernel.org/
====================

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

1 files changed, 67 insertions, 9 deletions

diff --git a/include/net/genetlink.h b/include/net/genetlink.h
index 9f97f73615b6..d21210709f84 100644
--- a/include/net/genetlink.h
+++ b/include/net/genetlink.h
@@ -18,12 +18,11 @@ struct genl_multicast_group {
 	u8			flags;
 };
 
-struct genl_ops;
+struct genl_split_ops;
 struct genl_info;
 
 /**
  * struct genl_family - generic netlink family
- * @id: protocol family identifier (private)
  * @hdrsize: length of user specific header in bytes
  * @name: name of family
  * @version: protocol version
@@ -43,12 +42,13 @@ struct genl_info;
  * @resv_start_op: first operation for which reserved fields of the header
  *	can be validated and policies are required (see below);
  *	new families should leave this field at zero
- * @mcgrp_offset: starting number of multicast group IDs in this family
- *	(private)
  * @ops: the operations supported by this family
  * @n_ops: number of operations supported by this family
  * @small_ops: the small-struct operations supported by this family
  * @n_small_ops: number of small-struct operations supported by this family
+ * @split_ops: the split do/dump form of operation definition
+ * @n_split_ops: number of entries in @split_ops, not that with split do/dump
+ *	ops the number of entries is not the same as number of commands
  *
  * Attribute policies (the combination of @policy and @maxattr fields)
  * can be attached at the family level or at the operation level.
@@ -58,29 +58,35 @@ struct genl_info;
  * if policy is not provided core will reject all TLV attributes.
  */
 struct genl_family {
-	int			id;		/* private */
 	unsigned int		hdrsize;
 	char			name[GENL_NAMSIZ];
 	unsigned int		version;
 	unsigned int		maxattr;
-	unsigned int		mcgrp_offset;	/* private */
 	u8			netnsok:1;
 	u8			parallel_ops:1;
 	u8			n_ops;
 	u8			n_small_ops;
+	u8			n_split_ops;
 	u8			n_mcgrps;
 	u8			resv_start_op;
 	const struct nla_policy *policy;
-	int			(*pre_doit)(const struct genl_ops *ops,
+	int			(*pre_doit)(const struct genl_split_ops *ops,
 					    struct sk_buff *skb,
 					    struct genl_info *info);
-	void			(*post_doit)(const struct genl_ops *ops,
+	void			(*post_doit)(const struct genl_split_ops *ops,
 					     struct sk_buff *skb,
 					     struct genl_info *info);
 	const struct genl_ops *	ops;
 	const struct genl_small_ops *small_ops;
+	const struct genl_split_ops *split_ops;
 	const struct genl_multicast_group *mcgrps;
 	struct module		*module;
+
+/* private: internal use only */
+	/* protocol family identifier */
+	int			id;
+	/* starting number of multicast group IDs in this family */
+	unsigned int		mcgrp_offset;
 };
 
 /**
@@ -182,6 +188,58 @@ struct genl_ops {
 };
 
 /**
+ * struct genl_split_ops - generic netlink operations (do/dump split version)
+ * @cmd: command identifier
+ * @internal_flags: flags used by the family
+ * @flags: GENL_* flags (%GENL_ADMIN_PERM or %GENL_UNS_ADMIN_PERM)
+ * @validate: validation flags from enum genl_validate_flags
+ * @policy: netlink policy (takes precedence over family policy)
+ * @maxattr: maximum number of attributes supported
+ *
+ * Do callbacks:
+ * @pre_doit: called before an operation's @doit callback, it may
+ *	do additional, common, filtering and return an error
+ * @doit: standard command callback
+ * @post_doit: called after an operation's @doit callback, it may
+ *	undo operations done by pre_doit, for example release locks
+ *
+ * Dump callbacks:
+ * @start: start callback for dumps
+ * @dumpit: callback for dumpers
+ * @done: completion callback for dumps
+ *
+ * Do callbacks can be used if %GENL_CMD_CAP_DO is set in @flags.
+ * Dump callbacks can be used if %GENL_CMD_CAP_DUMP is set in @flags.
+ * Exactly one of those flags must be set.
+ */
+struct genl_split_ops {
+	union {
+		struct {
+			int (*pre_doit)(const struct genl_split_ops *ops,
+					struct sk_buff *skb,
+					struct genl_info *info);
+			int (*doit)(struct sk_buff *skb,
+				    struct genl_info *info);
+			void (*post_doit)(const struct genl_split_ops *ops,
+					  struct sk_buff *skb,
+					  struct genl_info *info);
+		};
+		struct {
+			int (*start)(struct netlink_callback *cb);
+			int (*dumpit)(struct sk_buff *skb,
+				      struct netlink_callback *cb);
+			int (*done)(struct netlink_callback *cb);
+		};
+	};
+	const struct nla_policy *policy;
+	unsigned int		maxattr;
+	u8			cmd;
+	u8			internal_flags;
+	u8			flags;
+	u8			validate;
+};
+
+/**
  * struct genl_dumpit_info - info that is available during dumpit op call
  * @family: generic netlink family - for internal genl code usage
  * @op: generic netlink ops - for internal genl code usage
@@ -189,7 +247,7 @@ struct genl_ops {
  */
 struct genl_dumpit_info {
 	const struct genl_family *family;
-	struct genl_ops op;
+	struct genl_split_ops op;
 	struct nlattr **attrs;
 };