[PATCH 5/7] landlock: Convert from sb_mount to granular mount hooks

[Song Liu <song@kernel.org>]

Replace hook_sb_mount() with granular mount hooks. Landlock denies
all mount operations for sandboxed processes regardless of flags,
so all new hooks share a common hook_mount_deny() helper. The
mount_move hook reuses hook_move_mount().

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

Signed-off-by: Song Liu <song@kernel.org>
---
 security/landlock/fs.c | 40 ++++++++++++++++++++++++++++++++++++----
 1 file changed, 36 insertions(+), 4 deletions(-)

diff --git a/security/landlock/fs.c b/security/landlock/fs.c
index e764470f588c..6e810550efcb 100644
--- a/security/landlock/fs.c
+++ b/security/landlock/fs.c
@@ -1417,9 +1417,7 @@ static void log_fs_change_topology_dentry(
  * inherit these new constraints.  Anyway, for backward compatibility reasons,
  * a dedicated user space option would be required (e.g. as a ruleset flag).
  */
-static int hook_sb_mount(const char *const dev_name,
-			 const struct path *const path, const char *const type,
-			 const unsigned long flags, void *const data)
+static int hook_mount_deny(const struct path *const path)
 {
 	size_t handle_layer;
 	const struct landlock_cred_security *const subject =
@@ -1433,6 +1431,35 @@ static int hook_sb_mount(const char *const dev_name,
 	return -EPERM;
 }
 
+static int hook_mount_bind(const struct path *const from,
+			   const struct path *const to, bool recurse)
+{
+	return hook_mount_deny(to);
+}
+
+static int hook_mount_new(struct fs_context *fc, const struct path *const mp,
+			  int mnt_flags, unsigned long flags, void *data)
+{
+	return hook_mount_deny(mp);
+}
+
+static int hook_mount_remount(struct fs_context *fc, const struct path *mp,
+			      int mnt_flags, unsigned long flags, void *data)
+{
+	return hook_mount_deny(mp);
+}
+
+static int hook_mount_reconfigure(const struct path *const mp,
+				  unsigned int mnt_flags, unsigned long flags)
+{
+	return hook_mount_deny(mp);
+}
+
+static int hook_mount_change_type(const struct path *const mp, int ms_flags)
+{
+	return hook_mount_deny(mp);
+}
+
 static int hook_move_mount(const struct path *const from_path,
 			   const struct path *const to_path)
 {
@@ -1824,7 +1851,12 @@ static struct security_hook_list landlock_hooks[] __ro_after_init = {
 	LSM_HOOK_INIT(inode_free_security_rcu, hook_inode_free_security_rcu),
 
 	LSM_HOOK_INIT(sb_delete, hook_sb_delete),
-	LSM_HOOK_INIT(sb_mount, hook_sb_mount),
+	LSM_HOOK_INIT(mount_bind, hook_mount_bind),
+	LSM_HOOK_INIT(mount_new, hook_mount_new),
+	LSM_HOOK_INIT(mount_remount, hook_mount_remount),
+	LSM_HOOK_INIT(mount_reconfigure, hook_mount_reconfigure),
+	LSM_HOOK_INIT(mount_change_type, hook_mount_change_type),
+	LSM_HOOK_INIT(mount_move, hook_move_mount),
 	LSM_HOOK_INIT(move_mount, hook_move_mount),
 	LSM_HOOK_INIT(sb_umount, hook_sb_umount),
 	LSM_HOOK_INIT(sb_remount, hook_sb_remount),
-- 
2.52.0