ovl: set OVL_WHITEOUTS before publishing the upper dir

Listing a directory while it is copied up causes a use-after-free of
the readdir cache.

A merge directory must never be iterated as a real upper directory:
that mode frees the cache in OVL_I(inode)->cache without looking at
its refcount, while files opened in merged mode still use it.
ovl_copy_up_workdir() publishes the upper dentry before it sets
OVL_WHITEOUTS, and ovl_dir_open() samples both without a lock, so an
open between the two stores finds the upper directory and takes it
for a real one.

With a delay between the two stores, an unprivileged process that
listed a directory during its copy-up saw only "." and "..", and its
next getdents freed the readdir cache of another descriptor.

Fix this by setting OVL_WHITEOUTS before ovl_inode_update(), so that
ovl_dir_reset() agrees with ovl_dir_open(), and by testing
OVL_TYPE_MERGE() of the path type in ovl_dir_open(), so that an open
that observes the upper dentry never iterates a merge dir as a real
dir, regardless of the order in which it observes the flag.

Fixes: b79e05aaa166 ("ovl: no direct iteration for dir with origin xattr")
Cc: stable@vger.kernel.org
Signed-off-by: Chris Mason <mason@kernel.org>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
[amir: test OVL_TYPE_MERGE() instead of smp_rmb() in ovl_dir_open()]
Link: https://lore.kernel.org/linux-unionfs/CAOQ4uxh-1J2OBjnDVbrrrjy1puSOW0kABvghN85ih6dtKUBTyA@mail.gmail.com/
Signed-off-by: Amir Goldstein <amir73il@gmail.com>

0 files changed, 0 insertions, 0 deletions