This is a note to let you know that I've just added the patch titled
fs/mount_setattr: tighten permission checks
to the 5.12-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
fs-mount_setattr-tighten-permission-checks.patch
and it can be found in the queue-5.12 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 2ca4dcc4909d787ee153272f7efc2bff3b498720 Mon Sep 17 00:00:00 2001
From: Christian Brauner <christian.brauner@xxxxxxxxxx>
Date: Tue, 11 May 2021 16:30:15 +0200
Subject: fs/mount_setattr: tighten permission checks
From: Christian Brauner <christian.brauner@xxxxxxxxxx>
commit 2ca4dcc4909d787ee153272f7efc2bff3b498720 upstream.
We currently don't have any filesystems that support idmapped mounts
which are mountable inside a user namespace. That was a deliberate
decision for now as a userns root can just mount the filesystem
themselves. So enforce this restriction explicitly until there's a real
use-case for this. This way we can notice it and will have a chance to
adapt and audit our translation helpers and fstests appropriately if we
need to support such filesystems.
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
CC: linux-fsdevel@xxxxxxxxxxxxxxx
Suggested-by: Seth Forshee <seth.forshee@xxxxxxxxxxxxx>
Signed-off-by: Christian Brauner <christian.brauner@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
fs/namespace.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -3853,8 +3853,12 @@ static int can_idmap_mount(const struct
if (!(m->mnt_sb->s_type->fs_flags & FS_ALLOW_IDMAP))
return -EINVAL;
+ /* Don't yet support filesystem mountable in user namespaces. */
+ if (m->mnt_sb->s_user_ns != &init_user_ns)
+ return -EINVAL;
+
/* We're not controlling the superblock. */
- if (!ns_capable(m->mnt_sb->s_user_ns, CAP_SYS_ADMIN))
+ if (!capable(CAP_SYS_ADMIN))
return -EPERM;
/* Mount has already been visible in the filesystem hierarchy. */
Patches currently in stable-queue which might be from christian.brauner@xxxxxxxxxx are
queue-5.12/fs-mount_setattr-tighten-permission-checks.patch
