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Al Viro
bab77c0d19
Intention for MNT_LOCKED had always been to protect the internal
mountpoints within a subtree that got copied across the userns boundary,
not the mountpoint that tree got attached to - after all, it _was_
exposed before the copying.
For roots of secondary copies that is enforced in attach_recursive_mnt() -
MNT_LOCKED is explicitly stripped for those. For the root of primary
copy we are almost always guaranteed that MNT_LOCKED won't be there,
so attach_recursive_mnt() doesn't bother. Unfortunately, one call
chain got overlooked - triggering e.g. NFS referral will have the
submount inherit the public flags from parent; that's fine for such
things as read-only, nosuid, etc., but not for MNT_LOCKED.
This is particularly pointless since the mount attached by finish_automount()
is usually expirable, which makes any protection granted by MNT_LOCKED
null and void; just wait for a while and that mount will go away on its own.
Include MNT_LOCKED into the set of flags to be ignored by do_add_mount() - it
really is an internal flag.
Reviewed-by: Christian Brauner <brauner@kernel.org>
Fixes: 5ff9d8a65c ("vfs: Lock in place mounts from more privileged users")
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.