sysctl: Add size to register_net_sysctl function

This commit adds size to the register_net_sysctl indirection function to
facilitate the removal of the sentinel elements (last empty markers)
from the ctl_table arrays. Though we don't actually remove any sentinels
in this commit, register_net_sysctl* now has the capability of
forwarding table_size for when that happens.

We create a new function register_net_sysctl_sz with an extra size
argument. A macro replaces the existing register_net_sysctl. The size in
the macro is SIZE_MAX instead of ARRAY_SIZE to avoid compilation errors
while we systematically migrate to register_net_sysctl_sz. Will change
to ARRAY_SIZE in subsequent commits.

Care is taken to add table_size to the stopping criteria in such a way
that when we remove the empty sentinel element, it will continue
stopping in the last element of the ctl_table array.

Signed-off-by: Joel Granados <[email protected]>
Suggested-by: Greg Kroah-Hartman <[email protected]>
Signed-off-by: Luis Chamberlain <[email protected]>

Author: Joelgranados

include/net/net_namespace.h

@@ -469,15 +469,17 @@ void unregister_pernet_device(struct pernet_operations *);
 
 struct ctl_table;
 
+#define register_net_sysctl(net, path, table)	\
+	register_net_sysctl_sz(net, path, table, SIZE_MAX)
 #ifdef CONFIG_SYSCTL
 int net_sysctl_init(void);
-struct ctl_table_header *register_net_sysctl(struct net *net, const char *path,
-					     struct ctl_table *table);
+struct ctl_table_header *register_net_sysctl_sz(struct net *net, const char *path,
+					     struct ctl_table *table, size_t table_size);
 void unregister_net_sysctl_table(struct ctl_table_header *header);
 #else
 static inline int net_sysctl_init(void) { return 0; }
-static inline struct ctl_table_header *register_net_sysctl(struct net *net,
-	const char *path, struct ctl_table *table)
+static inline struct ctl_table_header *register_net_sysctl_sz(struct net *net,
+	const char *path, struct ctl_table *table, size_t table_size)
 {
 	return NULL;
 }

net/sysctl_net.c

@@ -122,12 +122,13 @@ __init int net_sysctl_init(void)
  *    allocated.
  */
 static void ensure_safe_net_sysctl(struct net *net, const char *path,
-				   struct ctl_table *table)
+				   struct ctl_table *table, size_t table_size)
 {
 	struct ctl_table *ent;
 
 	pr_debug("Registering net sysctl (net %p): %s\n", net, path);
-	for (ent = table; ent->procname; ent++) {
+	ent = table;
+	for (size_t i = 0; i < table_size && ent->procname; ent++, i++) {
 		unsigned long addr;
 		const char *where;
 
@@ -160,21 +161,24 @@ static void ensure_safe_net_sysctl(struct net *net, const char *path,
 	}
 }
 
-struct ctl_table_header *register_net_sysctl(struct net *net,
-	const char *path, struct ctl_table *table)
+struct ctl_table_header *register_net_sysctl_sz(struct net *net,
+						const char *path,
+						struct ctl_table *table,
+						size_t table_size)
 {
-	int count = 0;
+	int count;
 	struct ctl_table *entry;
 
 	if (!net_eq(net, &init_net))
-		ensure_safe_net_sysctl(net, path, table);
+		ensure_safe_net_sysctl(net, path, table, table_size);
 
-	for (entry = table; entry->procname; entry++)
-		count++;
+	entry = table;
+	for (count = 0 ; count < table_size && entry->procname; entry++, count++)
+		;
 
 	return __register_sysctl_table(&net->sysctls, path, table, count);
 }
-EXPORT_SYMBOL_GPL(register_net_sysctl);
+EXPORT_SYMBOL_GPL(register_net_sysctl_sz);
 
 void unregister_net_sysctl_table(struct ctl_table_header *header)
 {