seeing an odd bug where we fail to correctly return an error from
.get_tree():

https://syzkaller.appspot.com/bug?extid=c0360e8367d6d8d04a66

we need to be able to distinguish between accidently returning a
positive error (as implied by the log) and no error.

Cc: David Howells <dhowells@redhat.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

Christian noticed that it is possible for a privileged user to mount
most filesystems with a non-initial user namespace in sb->s_user_ns.
When fsopen() is called in a non-init namespace the caller's namespace
is recorded in fs_context->user_ns. If the returned file descriptor is
then passed to a process priviliged in init_user_ns, that process can
call fsconfig(fd_fs, FSCONFIG_CMD_CREATE), creating a new superblock
with sb->s_user_ns set to the namespace of the process which called
fsopen().

This is problematic. We cannot assume that any filesystem which does not
set FS_USERNS_MOUNT has been written with a non-initial s_user_ns in
mind, increasing the risk for bugs and security issues.

Prevent this by returning EPERM from sget_fc() when FS_USERNS_MOUNT is
not set for the filesystem and a non-initial user namespace will be
used. sget() does not need to be updated as it always uses the user
namespace of the current context, or the initial user namespace if
SB_SUBMOUNT is set.

Fixes: cb50b348c71f ("convenience helpers: vfs_get_super() and sget_fc()")
Reported-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Seth Forshee (DigitalOcean) <sforshee@kernel.org>
Link: https://lore.kernel.org/r/20240724-s_user_ns-fix-v1-1-895d07c94701@kernel.org
Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@canonical.com>
Signed-off-by: Christian Brauner <brauner@kernel.org>

The block device may have been frozen before it was claimed by a
filesystem. Concurrently another process might try to mount that
frozen block device and has temporarily claimed the block device for
that purpose causing a concurrent fs_bdev_thaw() to end up here. The
mounter is already about to abort mounting because they still saw an
elevanted bdev->bd_fsfreeze_count so get_bdev_super() will return
NULL in that case.

For example, P1 calls dm_suspend() which calls into bdev_freeze() before
the block device has been claimed by the filesystem. This brings
bdev->bd_fsfreeze_count to 1 and no call into fs_bdev_freeze() is
required.

Now P2 tries to mount that frozen block device. It claims it and checks
bdev->bd_fsfreeze_count. As it's elevated it aborts mounting.

In the meantime P3 called dm_resume(). P3 sees that the block device is
already claimed by a filesystem and calls into fs_bdev_thaw().

P3 takes a passive reference and realizes that the filesystem isn't
ready yet. P3 puts itself to sleep to wait for the filesystem to become
ready.

P2 now puts the last active reference to the filesystem and marks it as
dying. P3 gets woken, sees that the filesystem is dying and
get_bdev_super() fails.

Fixes: 49ef8832fb1a ("bdev: implement freeze and thaw holder operations")
Cc: <stable@vger.kernel.org>
Reported-by: Theodore Ts'o <tytso@mit.edu>
Link: https://lore.kernel.org/r/20240611085210.GA1838544@mit.edu
Link: https://lore.kernel.org/r/20240613-lackmantel-einsehen-90f0d727358d@brauner
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Pull fsnotify updates from Jan Kara:

 - reduce overhead of fsnotify infrastructure when no permission events
   are in use

 - a few small cleanups

* tag 'fsnotify_for_v6.10-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/jack/linux-fs:
  fsnotify: fix UAF from FS_ERROR event on a shutting down filesystem
  fsnotify: optimize the case of no permission event watchers
  fsnotify: use an enum for group priority constants
  fsnotify: move s_fsnotify_connectors into fsnotify_sb_info
  fsnotify: lazy attach fsnotify_sb_info state to sb
  fsnotify: create helper fsnotify_update_sb_watchers()
  fsnotify: pass object pointer and type to fsnotify mark helpers
  fanotify: merge two checks regarding add of ignore mark
  fsnotify: create a wrapper fsnotify_find_inode_mark()
  fsnotify: create helpers to get sb and connp from object
  fsnotify: rename fsnotify_{get,put}_sb_connectors()
  fsnotify: Avoid -Wflex-array-member-not-at-end warning
  fanotify: remove unneeded sub-zero check for unsigned value

Protect against use after free when filesystem calls fsnotify_sb_error()
during fs shutdown.

Move freeing of sb->s_fsnotify_info to destroy_super_work(), because it
may be accessed from fs shutdown context.

Reported-by: syzbot+5e3f9b2a67b45f16d4e6@syzkaller.appspotmail.com
Suggested-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/linux-fsdevel/20240416173211.4lnmgctyo4jn5fha@quack3/
Fixes: 07a3b8d0bf72 ("fsnotify: lazy attach fsnotify_sb_info state to sb")
Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Message-Id: <20240416181452.567070-1-amir73il@gmail.com>

Currently a device is only really released once the umount returns to
userspace due to how file closing works. That ultimately could cause
an old umount assumption to be violated that concurrent umount and mount
don't fail. So an exclusively held device with a temporary holder should
be yielded before the filesystem is gone. Add a helper that allows
callers to do that. This also allows us to remove the two holder ops
that Linus wasn't excited about.

Link: https://lore.kernel.org/r/20240326-vfs-bdev-end_holder-v1-1-20af85202918@kernel.org
Fixes: f3a608827d1f ("bdev: open block device as files") # mainline only
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

Now that we open block devices as files we need to deal with the
realities that closing is a deferred operation. An operation on the
block device such as e.g., freeze, thaw, or removal that runs
concurrently with umount, tries to acquire a stable reference on the
holder. The holder might already be gone though. Make that reliable by
grabbing a passive reference to the holder during bdev_open() and
releasing it during bdev_release().

Fixes: f3a608827d1f ("bdev: open block device as files") # mainline only
Reported-by: Christoph Hellwig <hch@infradead.org>
Link: https://lore.kernel.org/r/ZfEQQ9jZZVes0WCZ@infradead.org
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Christoph Hellwig <hch@infradead.org>
Tested-by: Yi Zhang <yi.zhang@redhat.com>
Reported-by: https://lore.kernel.org/r/CAHj4cs8tbDwKRwfS1=DmooP73ysM__xAb2PQc6XsAmWR+VuYmg@mail.gmail.com
Link: https://lore.kernel.org/r/20240315-freibad-annehmbar-ca68c375af91@brauner
Signed-off-by: Christian Brauner <brauner@kernel.org>

Pull block handle updates from Christian Brauner:
 "Last cycle we changed opening of block devices, and opening a block
  device would return a bdev_handle. This allowed us to implement
  support for restricting and forbidding writes to mounted block
  devices. It was accompanied by converting and adding helpers to
  operate on bdev_handles instead of plain block devices.

  That was already a good step forward but ultimately it isn't necessary
  to have special purpose helpers for opening block devices internally
  that return a bdev_handle.

  Fundamentally, opening a block device internally should just be
  equivalent to opening files. So now all internal opens of block
  devices return files just as a userspace open would. Instead of
  introducing a separate indirection into bdev_open_by_*() via struct
  bdev_handle bdev_file_open_by_*() is made to just return a struct
  file. Opening and closing a block device just becomes equivalent to
  opening and closing a file.

  This all works well because internally we already have a pseudo fs for
  block devices and so opening block devices is simple. There's a few
  places where we needed to be careful such as during boot when the
  kernel is supposed to mount the rootfs directly without init doing it.
  Here we need to take care to ensure that we flush out any asynchronous
  file close. That's what we already do for opening, unpacking, and
  closing the initramfs. So nothing new here.

  The equivalence of opening and closing block devices to regular files
  is a win in and of itself. But it also has various other advantages.
  We can remove struct bdev_handle completely. Various low-level helpers
  are now private to the block layer. Other helpers were simply
  removable completely.

  A follow-up series that is already reviewed build on this and makes it
  possible to remove bdev->bd_inode and allows various clean ups of the
  buffer head code as well. All places where we stashed a bdev_handle
  now just stash a file and use simple accessors to get to the actual
  block device which was already the case for bdev_handle"

* tag 'vfs-6.9.super' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs: (35 commits)
  block: remove bdev_handle completely
  block: don't rely on BLK_OPEN_RESTRICT_WRITES when yielding write access
  bdev: remove bdev pointer from struct bdev_handle
  bdev: make struct bdev_handle private to the block layer
  bdev: make bdev_{release, open_by_dev}() private to block layer
  bdev: remove bdev_open_by_path()
  reiserfs: port block device access to file
  ocfs2: port block device access to file
  nfs: port block device access to files
  jfs: port block device access to file
  f2fs: port block device access to files
  ext4: port block device access to file
  erofs: port device access to file
  btrfs: port device access to file
  bcachefs: port block device access to file
  target: port block device access to file
  s390: port block device access to file
  nvme: port block device access to file
  block2mtd: port device access to files
  bcache: port block device access to files
  ...

Add two new helpers to allow opening block devices as files.
This is not the final infrastructure. This still opens the block device
before opening a struct a file. Until we have removed all references to
struct bdev_handle we can't switch the order:

* Introduce blk_to_file_flags() to translate from block specific to
  flags usable to pen a new file.
* Introduce bdev_file_open_by_{dev,path}().
* Introduce temporary sb_bdev_handle() helper to retrieve a struct
  bdev_handle from a block device file and update places that directly
  reference struct bdev_handle to rely on it.
* Don't count block device openes against the number of open files. A
  bdev_file_open_by_{dev,path}() file is never installed into any
  file descriptor table.

One idea that came to mind was to use kernel_tmpfile_open() which
would require us to pass a path and it would then call do_dentry_open()
going through the regular fops->open::blkdev_open() path. But then we're
back to the problem of routing block specific flags such as
BLK_OPEN_RESTRICT_WRITES through the open path and would have to waste
FMODE_* flags every time we add a new one. With this we can avoid using
a flag bit and we have more leeway in how we open block devices from
bdev_open_by_{dev,path}().

Link: https://lore.kernel.org/r/20240123-vfs-bdev-file-v2-1-adbd023e19cc@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

Avoids fun races in RCU pathwalk...  Same goes for freeing LSM shite
hanging off super_block's arse.

Reviewed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>