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iomap: add a workaround for racy i_size updates on block devices

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A szybot reproducer that does write I/O while truncating the size of a
block device can end up in clean_bdev_aliases, which tries to clean the
bdev aliases that it uses.  This is because iomap_to_bh automatically
sets the BH_New flag when outside of i_size.  For block devices updates
to i_size are racy and we can hit this case in a tiny race window,
leading to the eventual clean_bdev_aliases call.  Fix this by erroring
out of > i_size I/O on block devices.

Reported-by: syzbot+1fa947e7f09e136925b8@syzkaller.appspotmail.com
Signed-off-by: Christoph Hellwig <hch@lst.de>
Tested-by: syzbot+1fa947e7f09e136925b8@syzkaller.appspotmail.com
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
This commit is contained in:
Christoph Hellwig 2023-09-25 08:54:45 -07:00 • committed by Darrick J. Wong
parent a5f31a5028
commit 381c043233
1 changed files with 10 additions and 1 deletions
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11
fs/buffer.c
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@ -2058,8 +2058,17 @@ iomap_to_bh(struct inode *inode, sector_t block, struct buffer_head *bh,
fallthrough;
case IOMAP_MAPPED:
if ((iomap->flags & IOMAP_F_NEW) ||
offset >= i_size_read(inode))
offset >= i_size_read(inode)) {
/*
* This can happen if truncating the block device races
* with the check in the caller as i_size updates on
* block devices aren't synchronized by i_rwsem for
* block devices.
*/
if (S_ISBLK(inode->i_mode))
return -EIO;
set_buffer_new(bh);
}
bh->b_blocknr = (iomap->addr + offset - iomap->offset) >>
inode->i_blkbits;
set_buffer_mapped(bh);