From 2ca4dcc4909d787ee153272f7efc2bff3b498720 Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Tue, 11 May 2021 16:30:15 +0200 Subject: fs/mount_setattr: tighten permission checks 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 Cc: Al Viro Cc: stable@vger.kernel.org CC: linux-fsdevel@vger.kernel.org Suggested-by: Seth Forshee Signed-off-by: Christian Brauner --- fs/namespace.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) (limited to 'fs/namespace.c') diff --git a/fs/namespace.c b/fs/namespace.c index f63337828e1c..c3f1a78ba369 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -3855,8 +3855,12 @@ static int can_idmap_mount(const struct mount_kattr *kattr, struct mount *mnt) 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. */ -- cgit v1.2.3-59-g8ed1b