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| author | Christian Brauner <brauner@kernel.org> | 2024-03-23 17:11:19 +0100 |
|---|---|---|
| committer | Christian Brauner <brauner@kernel.org> | 2024-03-27 09:31:41 +0100 |
| commit | ddd65e19c60140673ea9f7249af0a672f1820623 (patch) | |
| tree | 73d4200ee68cb4c37e8ffd23921523dbbccf3dae /block | |
| parent | 4cece764965020c22cff7665b18a012006359095 (diff) | |
| download | linux-ddd65e19c60140673ea9f7249af0a672f1820623.tar.gz linux-ddd65e19c60140673ea9f7249af0a672f1820623.tar.bz2 linux-ddd65e19c60140673ea9f7249af0a672f1820623.zip | |
block: handle BLK_OPEN_RESTRICT_WRITES correctly
Last kernel release we introduce CONFIG_BLK_DEV_WRITE_MOUNTED. By
default this option is set. When it is set the long-standing behavior
of being able to write to mounted block devices is enabled.
But in order to guard against unintended corruption by writing to the
block device buffer cache CONFIG_BLK_DEV_WRITE_MOUNTED can be turned
off. In that case it isn't possible to write to mounted block devices
anymore.
A filesystem may open its block devices with BLK_OPEN_RESTRICT_WRITES
which disallows concurrent BLK_OPEN_WRITE access. When we still had the
bdev handle around we could recognize BLK_OPEN_RESTRICT_WRITES because
the mode was passed around. Since we managed to get rid of the bdev
handle we changed that logic to recognize BLK_OPEN_RESTRICT_WRITES based
on whether the file was opened writable and writes to that block device
are blocked. That logic doesn't work because we do allow
BLK_OPEN_RESTRICT_WRITES to be specified without BLK_OPEN_WRITE.
Fix the detection logic and use an FMODE_* bit. We could've also abused
O_EXCL as an indicator that BLK_OPEN_RESTRICT_WRITES has been requested.
For userspace open paths O_EXCL will never be retained but for internal
opens where we open files that are never installed into a file
descriptor table this is fine. But it would be a gamble that this
doesn't cause bugs. Note that BLK_OPEN_RESTRICT_WRITES is an internal
only flag that cannot directly be raised by userspace. It is implicitly
raised during mounting.
Passes xftests and blktests with CONFIG_BLK_DEV_WRITE_MOUNTED set and
unset.
Link: https://lore.kernel.org/r/ZfyyEwu9Uq5Pgb94@casper.infradead.org
Link: https://lore.kernel.org/r/20240323-zielbereich-mittragen-6fdf14876c3e@brauner
Fixes: 321de651fa56 ("block: don't rely on BLK_OPEN_RESTRICT_WRITES when yielding write access")
Reviewed-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Reported-by: Matthew Wilcox <willy@infradead.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Diffstat (limited to 'block')
| -rw-r--r-- | block/bdev.c | 14 |
1 files changed, 7 insertions, 7 deletions
diff --git a/block/bdev.c b/block/bdev.c index 7a5f611c3d2e..ab9cae0e05f1 100644 --- a/block/bdev.c +++ b/block/bdev.c @@ -821,13 +821,11 @@ static void bdev_yield_write_access(struct file *bdev_file) return; bdev = file_bdev(bdev_file); - /* Yield exclusive or shared write access. */ - if (bdev_file->f_mode & FMODE_WRITE) { - if (bdev_writes_blocked(bdev)) - bdev_unblock_writes(bdev); - else - bdev->bd_writers--; - } + + if (bdev_file->f_mode & FMODE_WRITE_RESTRICTED) + bdev_unblock_writes(bdev); + else if (bdev_file->f_mode & FMODE_WRITE) + bdev->bd_writers--; } /** @@ -907,6 +905,8 @@ int bdev_open(struct block_device *bdev, blk_mode_t mode, void *holder, bdev_file->f_mode |= FMODE_BUF_RASYNC | FMODE_CAN_ODIRECT; if (bdev_nowait(bdev)) bdev_file->f_mode |= FMODE_NOWAIT; + if (mode & BLK_OPEN_RESTRICT_WRITES) + bdev_file->f_mode |= FMODE_WRITE_RESTRICTED; bdev_file->f_mapping = bdev->bd_inode->i_mapping; bdev_file->f_wb_err = filemap_sample_wb_err(bdev_file->f_mapping); bdev_file->private_data = holder; |