From: Al Viro <viro@zeniv.linux.org.uk>
Date: Wed, 4 Jun 2025 16:27:08 +0000 (-0400)
Subject: do_change_type(): refuse to operate on unmounted/not ours mounts
X-Git-Tag: v6.16-rc1~7^2
X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=12f147ddd6de7382dad54812e65f3f08d05809fc;p=linux-block.git

do_change_type(): refuse to operate on unmounted/not ours mounts

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>
---

diff --git a/fs/namespace.c b/fs/namespace.c
index 1c54c16c7bab..2721d64ecfdf 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -2959,6 +2959,10 @@ 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)