[PATCH 1/2] RFC: sysctl: write ctl_table->extra2 to table entries created from a ctl_path

[Lucian Adrian Grijincu <lucian.grijincu@gmail.com>]

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For each entry in an array of 'struct ctl_path' we were registering a
'struct ctl_table' array with two entries:
A) one to store the name + permissions,
B) one as an end-of-array marker (completely blank).

but we were not using any of the data storage fields
(data, extra1, extra2) in the first 'struct ctl_table'.

This adds possibility of storring some user provided
pointer in the 'extra2' field.

All users these functions store NULL in the 'extra2'
field like they used to before this patch:
* register_sysctl_paths
* register_net_sysctl_table
* register_net_sysctl_rotable

Until now sysctl_check_table considered that the 'struct ctl_table' of
directories may not store anything in the 'extra2' field. We no longer
consider this a fault.

Signed-off-by: Lucian Adrian Grijincu <lucian.grijincu@gmail.com>
---
 include/linux/sysctl.h      |    2 +-
 include/net/net_namespace.h |    2 ++
 kernel/sysctl.c             |    7 +++++--
 kernel/sysctl_check.c       |    2 --
 net/sysctl_net.c            |   20 ++++++++++++++------
 5 files changed, 22 insertions(+), 11 deletions(-)

[-- Attachment #2: 0001-RFC-sysctl-write-ctl_table-extra2-to-table-entries-c.patch --]
[-- Type: text/x-patch, Size: 5048 bytes --]

diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index 7bb5cb6..333c72b 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -1058,7 +1058,7 @@ struct ctl_path {
 void register_sysctl_root(struct ctl_table_root *root);
 struct ctl_table_header *__register_sysctl_paths(
 	struct ctl_table_root *root, struct nsproxy *namespaces,
-	const struct ctl_path *path, struct ctl_table *table);
+	const struct ctl_path *path, struct ctl_table *table, void *pathdata);
 struct ctl_table_header *register_sysctl_table(struct ctl_table * table);
 struct ctl_table_header *register_sysctl_paths(const struct ctl_path *path,
 						struct ctl_table *table);
diff --git a/include/net/net_namespace.h b/include/net/net_namespace.h
index b3b4a34..4c80c30 100644
--- a/include/net/net_namespace.h
+++ b/include/net/net_namespace.h
@@ -274,6 +274,8 @@ struct ctl_table_header;
 
 extern struct ctl_table_header *register_net_sysctl_table(struct net *net,
 	const struct ctl_path *path, struct ctl_table *table);
+struct ctl_table_header *register_net_sysctl_table_pathdata(struct net *net,
+	const struct ctl_path *path, struct ctl_table *table, void *pathdata);
 extern struct ctl_table_header *register_net_sysctl_rotable(
 	const struct ctl_path *path, struct ctl_table *table);
 extern void unregister_net_sysctl_table(struct ctl_table_header *header);
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index bc86bb3..279a0c8 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -1773,6 +1773,8 @@ static void try_attach(struct ctl_table_header *p, struct ctl_table_header *q)
  * @namespaces: Data to compute which lists of sysctl entries are visible
  * @path: The path to the directory the sysctl table is in.
  * @table: the top-level table structure
+ * @pathdata: user provided pointer to data that will be stored in
+ *            every ctl_table node of the path allocated for @path
  *
  * Register a sysctl table hierarchy. @table should be a filled in ctl_table
  * array. A completely 0 filled entry terminates the table.
@@ -1823,7 +1825,7 @@ static void try_attach(struct ctl_table_header *p, struct ctl_table_header *q)
 struct ctl_table_header *__register_sysctl_paths(
 	struct ctl_table_root *root,
 	struct nsproxy *namespaces,
-	const struct ctl_path *path, struct ctl_table *table)
+	const struct ctl_path *path, struct ctl_table *table, void *pathdata)
 {
 	struct ctl_table_header *header;
 	struct ctl_table *new, **prevp;
@@ -1855,6 +1857,7 @@ struct ctl_table_header *__register_sysctl_paths(
 		/* Copy the procname */
 		new->procname = path->procname;
 		new->mode     = 0555;
+		new->extra2   = pathdata;
 
 		*prevp = new;
 		prevp = &new->child;
@@ -1910,7 +1913,7 @@ struct ctl_table_header *register_sysctl_paths(const struct ctl_path *path,
 						struct ctl_table *table)
 {
 	return __register_sysctl_paths(&sysctl_table_root, current->nsproxy,
-					path, table);
+				       path, table, NULL);
 }
 
 /**
diff --git a/kernel/sysctl_check.c b/kernel/sysctl_check.c
index 10b90d8..8fd9b71 100644
--- a/kernel/sysctl_check.c
+++ b/kernel/sysctl_check.c
@@ -127,8 +127,6 @@ int sysctl_check_table(struct nsproxy *namespaces, struct ctl_table *table)
 				set_fail(&fail, table, "Directory with proc_handler");
 			if (table->extra1)
 				set_fail(&fail, table, "Directory with extra1");
-			if (table->extra2)
-				set_fail(&fail, table, "Directory with extra2");
 		} else {
 			if ((table->proc_handler == proc_dostring) ||
 			    (table->proc_handler == proc_dointvec) ||
diff --git a/net/sysctl_net.c b/net/sysctl_net.c
index ca84212..9c92cac 100644
--- a/net/sysctl_net.c
+++ b/net/sysctl_net.c
@@ -103,22 +103,30 @@ out:
 }
 subsys_initcall(sysctl_init);
 
-struct ctl_table_header *register_net_sysctl_table(struct net *net,
-	const struct ctl_path *path, struct ctl_table *table)
+struct ctl_table_header *register_net_sysctl_table_pathdata(struct net *net,
+	const struct ctl_path *path, struct ctl_table *table, void *pathdata)
 {
 	struct nsproxy namespaces;
 	namespaces = *current->nsproxy;
 	namespaces.net_ns = net;
-	return __register_sysctl_paths(&net_sysctl_root,
-					&namespaces, path, table);
+	return __register_sysctl_paths(&net_sysctl_root, &namespaces,
+				       path, table, pathdata);
+}
+EXPORT_SYMBOL_GPL(register_net_sysctl_table_pathdata);
+
+struct ctl_table_header *register_net_sysctl_table(struct net *net,
+	const struct ctl_path *path, struct ctl_table *table)
+{
+	return register_net_sysctl_table_pathdata(net, path, table, NULL);
 }
 EXPORT_SYMBOL_GPL(register_net_sysctl_table);
 
+
 struct ctl_table_header *register_net_sysctl_rotable(const
 		struct ctl_path *path, struct ctl_table *table)
 {
-	return __register_sysctl_paths(&net_sysctl_ro_root,
-			&init_nsproxy, path, table);
+	return __register_sysctl_paths(&net_sysctl_ro_root, &init_nsproxy,
+				       path, table, NULL);
 }
 EXPORT_SYMBOL_GPL(register_net_sysctl_rotable);