linux-hardening - [PATCH v2 13/18] sysctl: move sysctl type to ctl_table

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Message-Id: <20231204-const-sysctl-v2-13-7a5060b11447@weissschuh.net>
Date: Mon, 04 Dec 2023 08:52:26 +0100
From: Thomas Weißschuh <linux@...ssschuh.net>
To: Kees Cook <keescook@...omium.org>, 
 "Gustavo A. R. Silva" <gustavoars@...nel.org>, 
 Luis Chamberlain <mcgrof@...nel.org>, Iurii Zaikin <yzaikin@...gle.com>, 
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
 Joel Granados <j.granados@...sung.com>
Cc: linux-hardening@...r.kernel.org, linux-kernel@...r.kernel.org, 
 linux-fsdevel@...r.kernel.org, 
 Thomas Weißschuh <linux@...ssschuh.net>
Subject: [PATCH v2 13/18] sysctl: move sysctl type to ctl_table_header

In a future commit the sysctl core will only use
"const struct ctl_table". As a preparation for that move this mutable
field from "struct ctl_table" to "struct ctl_table_header".

This is also more correct in general as this is in fact a property of
the header and not the table itself.

Signed-off-by: Thomas Weißschuh <linux@...ssschuh.net>
---
 fs/proc/proc_sysctl.c  | 11 ++++++-----
 include/linux/sysctl.h | 22 +++++++++++-----------
 2 files changed, 17 insertions(+), 16 deletions(-)

diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
index 689a30196d0c..a398cc77637f 100644
--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -31,7 +31,7 @@ static const struct inode_operations proc_sys_dir_operations;
 
 /* Support for permanently empty directories */
 static struct ctl_table sysctl_mount_point[] = {
-	{.type = SYSCTL_TABLE_TYPE_PERMANENTLY_EMPTY }
+	{ }
 };
 
 /**
@@ -49,11 +49,11 @@ struct ctl_table_header *register_sysctl_mount_point(const char *path)
 EXPORT_SYMBOL(register_sysctl_mount_point);
 
 #define sysctl_is_perm_empty_ctl_header(hptr)		\
-	(hptr->ctl_table[0].type == SYSCTL_TABLE_TYPE_PERMANENTLY_EMPTY)
+	(hptr->type == SYSCTL_TABLE_TYPE_PERMANENTLY_EMPTY)
 #define sysctl_set_perm_empty_ctl_header(hptr)		\
-	(hptr->ctl_table[0].type = SYSCTL_TABLE_TYPE_PERMANENTLY_EMPTY)
+	(hptr->type = SYSCTL_TABLE_TYPE_PERMANENTLY_EMPTY)
 #define sysctl_clear_perm_empty_ctl_header(hptr)	\
-	(hptr->ctl_table[0].type = SYSCTL_TABLE_TYPE_DEFAULT)
+	(hptr->type = SYSCTL_TABLE_TYPE_DEFAULT)
 
 void proc_sys_poll_notify(struct ctl_table_poll *poll)
 {
@@ -231,7 +231,8 @@ static int insert_header(struct ctl_dir *dir, struct ctl_table_header *header)
 		return -EROFS;
 
 	/* Am I creating a permanently empty directory? */
-	if (sysctl_is_perm_empty_ctl_header(header)) {
+	if (header->ctl_table == sysctl_mount_point ||
+	    sysctl_is_perm_empty_ctl_header(header)) {
 		if (!RB_EMPTY_ROOT(&dir->root))
 			return -EINVAL;
 		sysctl_set_perm_empty_ctl_header(dir_h);
diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index ada36ef8cecb..061ea65104be 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -137,17 +137,6 @@ struct ctl_table {
 	void *data;
 	int maxlen;
 	umode_t mode;
-	/**
-	 * enum type - Enumeration to differentiate between ctl target types
-	 * @SYSCTL_TABLE_TYPE_DEFAULT: ctl target with no special considerations
-	 * @SYSCTL_TABLE_TYPE_PERMANENTLY_EMPTY: Used to identify a permanently
-	 *                                       empty directory target to serve
-	 *                                       as mount point.
-	 */
-	enum {
-		SYSCTL_TABLE_TYPE_DEFAULT,
-		SYSCTL_TABLE_TYPE_PERMANENTLY_EMPTY
-	} type;
 	proc_handler *proc_handler;	/* Callback for text formatting */
 	struct ctl_table_poll *poll;
 	void *extra1;
@@ -188,6 +177,17 @@ struct ctl_table_header {
 	struct ctl_dir *parent;
 	struct ctl_node *node;
 	struct hlist_head inodes; /* head for proc_inode->sysctl_inodes */
+	/**
+	 * enum type - Enumeration to differentiate between ctl target types
+	 * @SYSCTL_TABLE_TYPE_DEFAULT: ctl target with no special considerations
+	 * @SYSCTL_TABLE_TYPE_PERMANENTLY_EMPTY: Used to identify a permanently
+	 *                                       empty directory target to serve
+	 *                                       as mount point.
+	 */
+	enum {
+		SYSCTL_TABLE_TYPE_DEFAULT,
+		SYSCTL_TABLE_TYPE_PERMANENTLY_EMPTY
+	} type;
 };
 
 struct ctl_dir {

-- 
2.43.0