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authorChristian Brauner <brauner@kernel.org>2024-03-23 17:11:19 +0100
committerChristian Brauner <brauner@kernel.org>2024-03-27 09:31:41 +0100
commitddd65e19c60140673ea9f7249af0a672f1820623 (patch)
tree73d4200ee68cb4c37e8ffd23921523dbbccf3dae /block/bdev.c
parent4cece764965020c22cff7665b18a012006359095 (diff)
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/bdev.c')
-rw-r--r--block/bdev.c14
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;