[PATCH] LSM: Disable move_mount() syscall when TOMOYO or AppArmor is enabled.

[Tetsuo Handa]

Commit 2db154b3ea8e14b0 ("vfs: syscall: Add move_mount(2) to move mounts
around") introduced security_move_mount() LSM hook, but we missed that
TOMOYO and AppArmor did not implement hooks for checking move_mount(2).
For pathname based access controls like TOMOYO and AppArmor, unchecked
mount manipulation is not acceptable. Therefore, until TOMOYO and AppArmor
implement hooks, in order to avoid unchecked mount manipulation, pretend
as if move_mount(2) is unavailable when either TOMOYO or AppArmor is
enabled.

Signed-off-by: Tetsuo Handa <penguin-kernel at I-love.SAKURA.ne.jp>
Acked-by: John Johansen <john.johansen at canonical.com>
Fixes: 2db154b3ea8e14b0 ("vfs: syscall: Add move_mount(2) to move mounts around")
Cc: stable at vger.kernel.org # 5.2
---
 include/linux/lsm_hooks.h | 6 ++++++
 security/apparmor/lsm.c   | 1 +
 security/tomoyo/tomoyo.c  | 1 +
 3 files changed, 8 insertions(+)

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 47f58cf..cd411b7 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -2142,4 +2142,10 @@ static inline void security_delete_hooks(struct security_hook_list *hooks,
 
 extern int lsm_inode_alloc(struct inode *inode);
 
+static inline int no_move_mount(const struct path *from_path,
+				const struct path *to_path)
+{
+	return -ENOSYS;
+}
+
 #endif /* ! __LINUX_LSM_HOOKS_H */
diff --git a/security/apparmor/lsm.c b/security/apparmor/lsm.c
index ec3a928..5cdf63b 100644
--- a/security/apparmor/lsm.c
+++ b/security/apparmor/lsm.c
@@ -1158,6 +1158,7 @@ struct lsm_blob_sizes apparmor_blob_sizes __lsm_ro_after_init = {
 	LSM_HOOK_INIT(capable, apparmor_capable),
 
 	LSM_HOOK_INIT(sb_mount, apparmor_sb_mount),
+	LSM_HOOK_INIT(move_mount, no_move_mount),
 	LSM_HOOK_INIT(sb_umount, apparmor_sb_umount),
 	LSM_HOOK_INIT(sb_pivotroot, apparmor_sb_pivotroot),
 
diff --git a/security/tomoyo/tomoyo.c b/security/tomoyo/tomoyo.c
index 716c92e..be1b1a1 100644
--- a/security/tomoyo/tomoyo.c
+++ b/security/tomoyo/tomoyo.c
@@ -558,6 +558,7 @@ static void tomoyo_task_free(struct task_struct *task)
 	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(move_mount, no_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),
-- 
1.8.3.1