[PATCH v3 4/7] selinux: Convert from sb_mount to granular mount hooks

[Song Liu <song@kernel.org>]

Replace selinux_mount() with granular mount hooks, preserving the
same permission checks:

- mount_bind, mount_new, mount_change_type: FILE__MOUNTON
- mount_remount, mount_reconfigure: FILESYSTEM__REMOUNT
- mount_move: FILE__MOUNTON (reuses selinux_move_mount)

The flags and data parameters are unused by SELinux.

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

Reviewed-by: Stephen Smalley <stephen.smalley.work@gmail.com>
Tested-by: Stephen Smalley <stephen.smalley.work@gmail.com>
Signed-off-by: Song Liu <song@kernel.org>
---
 security/selinux/hooks.c | 47 ++++++++++++++++++++++++++++++----------
 1 file changed, 35 insertions(+), 12 deletions(-)

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 0f704380a8c8..864a3ca772c9 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -2802,19 +2802,37 @@ static int selinux_sb_statfs(struct dentry *dentry)
 	return superblock_has_perm(cred, dentry->d_sb, FILESYSTEM__GETATTR, &ad);
 }
 
-static int selinux_mount(const char *dev_name,
-			 const struct path *path,
-			 const char *type,
-			 unsigned long flags,
-			 void *data)
+static int selinux_mount_bind(const struct path *from, const struct path *to,
+			      bool recurse)
 {
-	const struct cred *cred = current_cred();
+	return path_has_perm(current_cred(), to, FILE__MOUNTON);
+}
 
-	if (flags & MS_REMOUNT)
-		return superblock_has_perm(cred, path->dentry->d_sb,
-					   FILESYSTEM__REMOUNT, NULL);
-	else
-		return path_has_perm(cred, path, FILE__MOUNTON);
+static int selinux_mount_new(struct fs_context *fc, const struct path *mp,
+			     int mnt_flags, unsigned long flags, void *data)
+{
+	return path_has_perm(current_cred(), mp, FILE__MOUNTON);
+}
+
+static int selinux_mount_remount(struct fs_context *fc, const struct path *mp,
+				 int mnt_flags, unsigned long flags,
+				 void *data)
+{
+	return superblock_has_perm(current_cred(), fc->root->d_sb,
+				   FILESYSTEM__REMOUNT, NULL);
+}
+
+static int selinux_mount_reconfigure(const struct path *mp,
+				     unsigned int mnt_flags,
+				     unsigned long flags)
+{
+	return superblock_has_perm(current_cred(), mp->dentry->d_sb,
+				   FILESYSTEM__REMOUNT, NULL);
+}
+
+static int selinux_mount_change_type(const struct path *mp, int ms_flags)
+{
+	return path_has_perm(current_cred(), mp, FILE__MOUNTON);
 }
 
 static int selinux_move_mount(const struct path *from_path,
@@ -7558,7 +7576,12 @@ static struct security_hook_list selinux_hooks[] __ro_after_init = {
 	LSM_HOOK_INIT(sb_kern_mount, selinux_sb_kern_mount),
 	LSM_HOOK_INIT(sb_show_options, selinux_sb_show_options),
 	LSM_HOOK_INIT(sb_statfs, selinux_sb_statfs),
-	LSM_HOOK_INIT(sb_mount, selinux_mount),
+	LSM_HOOK_INIT(mount_bind, selinux_mount_bind),
+	LSM_HOOK_INIT(mount_new, selinux_mount_new),
+	LSM_HOOK_INIT(mount_remount, selinux_mount_remount),
+	LSM_HOOK_INIT(mount_reconfigure, selinux_mount_reconfigure),
+	LSM_HOOK_INIT(mount_change_type, selinux_mount_change_type),
+	LSM_HOOK_INIT(mount_move, selinux_move_mount),
 	LSM_HOOK_INIT(sb_umount, selinux_umount),
 	LSM_HOOK_INIT(sb_set_mnt_opts, selinux_set_mnt_opts),
 	LSM_HOOK_INIT(sb_clone_mnt_opts, selinux_sb_clone_mnt_opts),
-- 
2.53.0-Meta