linux-kernel - [PATCH v5 0/2] Prevent re-use of FUSE block-device-based superblock after force unmount

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Message-Id: <20220727064425.4144478-1-dlunev@chromium.org>
Date:   Wed, 27 Jul 2022 16:44:23 +1000
From:   Daniil Lunev <dlunev@...omium.org>
To:     Miklos Szeredi <miklos@...redi.hu>,
        Alexander Viro <viro@...iv.linux.org.uk>
Cc:     linux-fsdevel@...r.kernel.org, fuse-devel@...ts.sourceforge.net,
        Christoph Hellwig <hch@....de>, linux-kernel@...r.kernel.org,
        Daniil Lunev <dlunev@...omium.org>
Subject: [PATCH v5 0/2] Prevent re-use of FUSE block-device-based superblock after force unmount

Force unmount of fuse severes the connection between FUSE driver and its
userspace counterpart. However, open file handles will prevent the
superblock from being reclaimed. An attempt to remount the filesystem at
the same endpoint will try re-using the superblock, if still present.
Since the superblock re-use path doesn't go through the fs-specific
superblock setup code, its state in FUSE case is already disfunctional,
and that will prevent the mount from succeeding.

Changes in v5:
- Update commit messages to specify that only block-device-based
  superblocks are affected
- Restrict retire_super call in FUSE to be issued for fuseblk only.

Changes in v4:
- Simplify condition according to Christoph Hellwig's comments.

Changes in v3:
- Back to state tracking from v1
- Use s_iflag to mark superblocked ignored
- Only unregister private bdi in retire, without freeing

Changes in v2:
- Remove super from list of superblocks instead of using a flag

Daniil Lunev (2):
  fs/super: function to prevent re-use of block-device-based superblocks
  FUSE: Retire block-device-based superblock on force unmount

 fs/fuse/inode.c    | 10 ++++++++--
 fs/super.c         | 32 ++++++++++++++++++++++++++++++--
 include/linux/fs.h |  2 ++
 3 files changed, 40 insertions(+), 4 deletions(-)

-- 
2.31.0