[PATCH v2 3/8] sysctl: add helper to register a sysctl mount point

Luis Chamberlain
2021-11-24T23:15:40Z

The way to create a subdirectory on top of sysctl_mount_point is
a bit obscure, and *why* we do that even so more. Provide a helper
which makes it clear why we do this.

Suggested-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
---
fs/proc/proc_sysctl.c | 13 +++++++++++++
include/linux/sysctl.h | 7 +++++++
2 files changed, 20 insertions(+)

diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index 6d462644bb00..aa743bbb8400 100644
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -35,6 +35,19 @@ struct ctl_table sysctl_mount_point[] = {
{ }
};

+/**
+ * register_sysctl_mount_point() - registers a sysctl mount point
+ * @path: path for the mount point
+ *
+ * Used to create a permanently empty directory to serve as mount point.
+ * There are some subtle but important permission checks this allows in the
+ * case of unprivileged mounts.
+ */
+struct ctl_table_header *register_sysctl_mount_point(const char *path)
+{
+ return register_sysctl(path, sysctl_mount_point);
+}
+
static bool is_empty_dir(struct ctl_table_header *head)
{
return head->ctl_table[0].child == sysctl_mount_point;
diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index e4da44567f18..7946b532e964 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -208,6 +208,8 @@ extern int sysctl_init(void);
extern void __register_sysctl_init(const char *path, struct ctl_table *table,
const char *table_name);
#define register_sysctl_init(path, table) __register_sysctl_init(path, table, #table)
+extern struct ctl_table_header *register_sysctl_mount_point(const char *path);
+
void do_sysctl_args(void);

extern int pwrsw_enabled;
@@ -223,6 +225,11 @@ static inline struct ctl_table_header *register_sysctl_table(struct ctl_table *
return NULL;
}

+static inline struct sysctl_header *register_sysctl_mount_point(const char *path)
+{
+ return NULL;
+}
+
static inline struct ctl_table_header *register_sysctl_paths(
const struct ctl_path *path, struct ctl_table *table)
{
--
2.33.0