From 4f091ad0862b02dc42a19a120b7048de848561f8 Mon Sep 17 00:00:00 2001
From: Al Viro <viro@zeniv.linux.org.uk>
Date: Wed, 4 Jun 2025 12:27:08 -0400
Subject: [PATCH] do_change_type(): refuse to operate on unmounted/not ours
 mounts

[ Upstream commit 12f147ddd6de7382dad54812e65f3f08d05809fc ]

Ensure that propagation settings can only be changed for mounts located
in the caller's mount namespace. This change aligns permission checking
with the rest of mount(2).

Reviewed-by: Christian Brauner <brauner@kernel.org>
Fixes: 07b20889e305 ("beginning of the shared-subtree proper")
Reported-by: "Orlando, Noah" <Noah.Orlando@deshaw.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 fs/namespace.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/fs/namespace.c b/fs/namespace.c
index 4d8afd0e1eb8..eab9185e2285 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2557,6 +2557,10 @@ static int do_change_type(struct path *path, int ms_flags)
 		return -EINVAL;
 
 	namespace_lock();
+	if (!check_mnt(mnt)) {
+		err = -EINVAL;
+		goto out_unlock;
+	}
 	if (type == MS_SHARED) {
 		err = invent_group_ids(mnt, recurse);
 		if (err)