[PATCH 6/7] tomoyo: Convert from sb_mount to granular mount hooks

[Song Liu <song@kernel.org>]

Replace tomoyo_sb_mount() with granular mount hooks. Each hook
reconstructs the MS_* flags expected by tomoyo_mount_permission()
using the original flags parameter where available.

Key changes:
- mount_bind: passes the pre-resolved source path to
  tomoyo_mount_acl() via a new dev_path parameter, instead of
  re-resolving dev_name via kern_path(). This eliminates a TOCTOU
  vulnerability.
- mount_new, mount_remount, mount_reconfigure: use the original
  mount(2) flags for policy matching.
- mount_move: passes pre-resolved paths for both source and
  destination.
- mount_change_type: passes raw ms_flags directly.

Also removes the unused data_page parameter from
tomoyo_mount_permission().

Code generated with the assistance of Claude, reviewed by human.

Signed-off-by: Song Liu <song@kernel.org>
---
 security/tomoyo/common.h |  2 +-
 security/tomoyo/mount.c  | 31 +++++++++++++-------
 security/tomoyo/tomoyo.c | 63 ++++++++++++++++++++++++++++++----------
 3 files changed, 70 insertions(+), 26 deletions(-)

diff --git a/security/tomoyo/common.h b/security/tomoyo/common.h
index 4f1704c911ef..e40441844eab 100644
--- a/security/tomoyo/common.h
+++ b/security/tomoyo/common.h
@@ -1013,7 +1013,7 @@ int tomoyo_mkdev_perm(const u8 operation, const struct path *path,
 		      const unsigned int mode, unsigned int dev);
 int tomoyo_mount_permission(const char *dev_name, const struct path *path,
 			    const char *type, unsigned long flags,
-			    void *data_page);
+			    const struct path *dev_path);
 int tomoyo_open_control(const u8 type, struct file *file);
 int tomoyo_path2_perm(const u8 operation, const struct path *path1,
 		      const struct path *path2);
diff --git a/security/tomoyo/mount.c b/security/tomoyo/mount.c
index 322dfd188ada..82ffe7d02814 100644
--- a/security/tomoyo/mount.c
+++ b/security/tomoyo/mount.c
@@ -70,6 +70,7 @@ static bool tomoyo_check_mount_acl(struct tomoyo_request_info *r,
  * @dir:      Pointer to "struct path".
  * @type:     Name of filesystem type.
  * @flags:    Mount options.
+ * @dev_path: Pre-resolved device/source path. Maybe NULL.
  *
  * Returns 0 on success, negative value otherwise.
  *
@@ -78,11 +79,11 @@ static bool tomoyo_check_mount_acl(struct tomoyo_request_info *r,
 static int tomoyo_mount_acl(struct tomoyo_request_info *r,
 			    const char *dev_name,
 			    const struct path *dir, const char *type,
-			    unsigned long flags)
+			    unsigned long flags,
+			    const struct path *dev_path)
 	__must_hold_shared(&tomoyo_ss)
 {
 	struct tomoyo_obj_info obj = { };
-	struct path path;
 	struct file_system_type *fstype = NULL;
 	const char *requested_type = NULL;
 	const char *requested_dir_name = NULL;
@@ -134,13 +135,23 @@ static int tomoyo_mount_acl(struct tomoyo_request_info *r,
 			need_dev = 1;
 	}
 	if (need_dev) {
-		/* Get mount point or device file. */
-		if (!dev_name || kern_path(dev_name, LOOKUP_FOLLOW, &path)) {
+		if (dev_path) {
+			/* Use pre-resolved path to avoid TOCTOU issues. */
+			obj.path1 = *dev_path;
+			path_get(&obj.path1);
+		} else if (!dev_name) {
 			error = -ENOENT;
 			goto out;
+		} else {
+			struct path path;
+
+			if (kern_path(dev_name, LOOKUP_FOLLOW, &path)) {
+				error = -ENOENT;
+				goto out;
+			}
+			obj.path1 = path;
 		}
-		obj.path1 = path;
-		requested_dev_name = tomoyo_realpath_from_path(&path);
+		requested_dev_name = tomoyo_realpath_from_path(&obj.path1);
 		if (!requested_dev_name) {
 			error = -ENOENT;
 			goto out;
@@ -173,7 +184,7 @@ static int tomoyo_mount_acl(struct tomoyo_request_info *r,
 	if (fstype)
 		put_filesystem(fstype);
 	kfree(requested_type);
-	/* Drop refcount obtained by kern_path(). */
+	/* Drop refcount obtained by kern_path() or path_get(). */
 	if (obj.path1.dentry)
 		path_put(&obj.path1);
 	return error;
@@ -186,13 +197,13 @@ static int tomoyo_mount_acl(struct tomoyo_request_info *r,
  * @path:      Pointer to "struct path".
  * @type:      Name of filesystem type. Maybe NULL.
  * @flags:     Mount options.
- * @data_page: Optional data. Maybe NULL.
+ * @dev_path:  Pre-resolved device/source path. Maybe NULL.
  *
  * Returns 0 on success, negative value otherwise.
  */
 int tomoyo_mount_permission(const char *dev_name, const struct path *path,
 			    const char *type, unsigned long flags,
-			    void *data_page)
+			    const struct path *dev_path)
 {
 	struct tomoyo_request_info r;
 	int error;
@@ -236,7 +247,7 @@ int tomoyo_mount_permission(const char *dev_name, const struct path *path,
 	if (!type)
 		type = "<NULL>";
 	idx = tomoyo_read_lock();
-	error = tomoyo_mount_acl(&r, dev_name, path, type, flags);
+	error = tomoyo_mount_acl(&r, dev_name, path, type, flags, dev_path);
 	tomoyo_read_unlock(idx);
 	return error;
 }
diff --git a/security/tomoyo/tomoyo.c b/security/tomoyo/tomoyo.c
index c66e02ed8ee3..ac84e1f03d5e 100644
--- a/security/tomoyo/tomoyo.c
+++ b/security/tomoyo/tomoyo.c
@@ -6,6 +6,8 @@
  */
 
 #include <linux/lsm_hooks.h>
+#include <linux/fs_context.h>
+#include <uapi/linux/mount.h>
 #include <uapi/linux/lsm.h>
 #include "common.h"
 
@@ -398,21 +400,47 @@ static int tomoyo_path_chroot(const struct path *path)
 	return tomoyo_path_perm(TOMOYO_TYPE_CHROOT, path, NULL);
 }
 
-/**
- * tomoyo_sb_mount - Target for security_sb_mount().
- *
- * @dev_name: Name of device file. Maybe NULL.
- * @path:     Pointer to "struct path".
- * @type:     Name of filesystem type. Maybe NULL.
- * @flags:    Mount options.
- * @data:     Optional data. Maybe NULL.
- *
- * Returns 0 on success, negative value otherwise.
- */
-static int tomoyo_sb_mount(const char *dev_name, const struct path *path,
-			   const char *type, unsigned long flags, void *data)
+static int tomoyo_mount_bind(const struct path *from, const struct path *to,
+			     bool recurse)
+{
+	unsigned long flags = MS_BIND | (recurse ? MS_REC : 0);
+
+	return tomoyo_mount_permission(NULL, to, NULL, flags, from);
+}
+
+static int tomoyo_mount_new(struct fs_context *fc, const struct path *mp,
+			    int mnt_flags, unsigned long flags, void *data)
+{
+	/* Use original MS_* flags for policy matching */
+	return tomoyo_mount_permission(fc->source, mp, fc->fs_type->name,
+				       flags, NULL);
+}
+
+static int tomoyo_mount_remount(struct fs_context *fc, const struct path *mp,
+				int mnt_flags, unsigned long flags, void *data)
+{
+	/* Use original MS_* flags for policy matching */
+	return tomoyo_mount_permission(NULL, mp, NULL, flags, NULL);
+}
+
+static int tomoyo_mount_reconfigure(const struct path *mp,
+				    unsigned int mnt_flags,
+				    unsigned long flags)
+{
+	/* Use original MS_* flags for policy matching */
+	return tomoyo_mount_permission(NULL, mp, NULL, flags, NULL);
+}
+
+static int tomoyo_mount_change_type(const struct path *mp, int ms_flags)
+{
+	return tomoyo_mount_permission(NULL, mp, NULL, ms_flags, NULL);
+}
+
+static int tomoyo_move_mount(const struct path *from_path,
+			     const struct path *to_path)
 {
-	return tomoyo_mount_permission(dev_name, path, type, flags, data);
+	return tomoyo_mount_permission(NULL, to_path, NULL, MS_MOVE,
+				       from_path);
 }
 
 /**
@@ -576,7 +604,12 @@ static struct security_hook_list tomoyo_hooks[] __ro_after_init = {
 	LSM_HOOK_INIT(path_chmod, tomoyo_path_chmod),
 	LSM_HOOK_INIT(path_chown, tomoyo_path_chown),
 	LSM_HOOK_INIT(path_chroot, tomoyo_path_chroot),
-	LSM_HOOK_INIT(sb_mount, tomoyo_sb_mount),
+	LSM_HOOK_INIT(mount_bind, tomoyo_mount_bind),
+	LSM_HOOK_INIT(mount_new, tomoyo_mount_new),
+	LSM_HOOK_INIT(mount_remount, tomoyo_mount_remount),
+	LSM_HOOK_INIT(mount_reconfigure, tomoyo_mount_reconfigure),
+	LSM_HOOK_INIT(mount_change_type, tomoyo_mount_change_type),
+	LSM_HOOK_INIT(mount_move, tomoyo_move_mount),
 	LSM_HOOK_INIT(sb_umount, tomoyo_sb_umount),
 	LSM_HOOK_INIT(sb_pivotroot, tomoyo_sb_pivotroot),
 	LSM_HOOK_INIT(socket_bind, tomoyo_socket_bind),
-- 
2.52.0