apparmor: Fix regression in mount mediation

commit 2db154b3 ("vfs: syscall: Add move_mount(2) to move mounts around")

introduced a new move_mount(2) system call and a corresponding new LSM
security_move_mount hook but did not implement this hook for any
existing LSM. This creates a regression for AppArmor mediation of
mount. This patch provides a base mapping of the move_mount syscall to
the existing mount mediation. In the future we may introduce
additional mediations around the new mount calls.

Fixes: 2db154b3 ("vfs: syscall: Add move_mount(2) to move mounts around")
CC: stable@vger.kernel.org
Reported-by: Andreas Steinmetz <anstein99@googlemail.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>

security/apparmor/include/mount.h

@@ -38,9 +38,12 @@ int aa_mount_change_type(const struct cred *subj_cred,
 			 struct aa_label *label, const struct path *path,
 			 unsigned long flags);
 
+int aa_move_mount_old(const struct cred *subj_cred,
+		      struct aa_label *label, const struct path *path,
+		      const char *old_name);
 int aa_move_mount(const struct cred *subj_cred,
-		  struct aa_label *label, const struct path *path,
-		  const char *old_name);
+		  struct aa_label *label, const struct path *from_path,
+		  const struct path *to_path);
 
 int aa_new_mount(const struct cred *subj_cred,
 		 struct aa_label *label, const char *dev_name,

security/apparmor/lsm.c

@@ -722,8 +722,8 @@ static int apparmor_sb_mount(const char *dev_name, const struct path *path,
 			error = aa_mount_change_type(current_cred(), label,
 						     path, flags);
 		else if (flags & MS_MOVE)
-			error = aa_move_mount(current_cred(), label, path,
-					      dev_name);
+			error = aa_move_mount_old(current_cred(), label, path,
+						  dev_name);
 		else
 			error = aa_new_mount(current_cred(), label, dev_name,
 					     path, type, flags, data);
@@ -733,6 +733,21 @@ static int apparmor_sb_mount(const char *dev_name, const struct path *path,
 	return error;
 }
 
+static int apparmor_move_mount(const struct path *from_path,
+			       const struct path *to_path)
+{
+	struct aa_label *label;
+	int error = 0;
+
+	label = __begin_current_label_crit_section();
+	if (!unconfined(label))
+		error = aa_move_mount(current_cred(), label, from_path,
+				      to_path);
+	__end_current_label_crit_section(label);
+
+	return error;
+}
+
 static int apparmor_sb_umount(struct vfsmount *mnt, int flags)
 {
 	struct aa_label *label;
@@ -1376,6 +1391,7 @@ static struct security_hook_list apparmor_hooks[] __ro_after_init = {
 	LSM_HOOK_INIT(capget, apparmor_capget),
 	LSM_HOOK_INIT(capable, apparmor_capable),
 
+	LSM_HOOK_INIT(move_mount, apparmor_move_mount),
 	LSM_HOOK_INIT(sb_mount, apparmor_sb_mount),
 	LSM_HOOK_INIT(sb_umount, apparmor_sb_umount),
 	LSM_HOOK_INIT(sb_pivotroot, apparmor_sb_pivotroot),

security/apparmor/mount.c

@@ -483,36 +483,46 @@ int aa_mount_change_type(const struct cred *subj_cred,
 }
 
 int aa_move_mount(const struct cred *subj_cred,
-		  struct aa_label *label, const struct path *path,
-		  const char *orig_name)
+		  struct aa_label *label, const struct path *from_path,
+		  const struct path *to_path)
 {
 	struct aa_profile *profile;
-	char *buffer = NULL, *old_buffer = NULL;
-	struct path old_path;
+	char *to_buffer = NULL, *from_buffer = NULL;
 	int error;
 
 	AA_BUG(!label);
-	AA_BUG(!path);
+	AA_BUG(!from_path);
+	AA_BUG(!to_path);
+
+	to_buffer = aa_get_buffer(false);
+	from_buffer = aa_get_buffer(false);
+	error = -ENOMEM;
+	if (!to_buffer || !from_buffer)
+		goto out;
+	error = fn_for_each_confined(label, profile,
+			match_mnt(subj_cred, profile, to_path, to_buffer,
+				  from_path, from_buffer,
+				  NULL, MS_MOVE, NULL, false));
+out:
+	aa_put_buffer(to_buffer);
+	aa_put_buffer(from_buffer);
+
+	return error;
+}
+
+int aa_move_mount_old(const struct cred *subj_cred, struct aa_label *label,
+		      const struct path *path, const char *orig_name)
+{
+	struct path old_path;
+	int error;
 
 	if (!orig_name || !*orig_name)
 		return -EINVAL;
-
 	error = kern_path(orig_name, LOOKUP_FOLLOW, &old_path);
 	if (error)
 		return error;
 
-	buffer = aa_get_buffer(false);
-	old_buffer = aa_get_buffer(false);
-	error = -ENOMEM;
-	if (!buffer || !old_buffer)
-		goto out;
-	error = fn_for_each_confined(label, profile,
-			match_mnt(subj_cred, profile, path, buffer, &old_path,
-				  old_buffer,
-				  NULL, MS_MOVE, NULL, false));
-out:
-	aa_put_buffer(buffer);
-	aa_put_buffer(old_buffer);
+	error = aa_move_mount(subj_cred, label, &old_path, path);
 	path_put(&old_path);
 
 	return error;