On Thu 03-09-20 16:04:14, Gabriel Krisman Bertazi wrote:
> Prior to commit 9fe55eea7e4b ("Fix race when checking i_size on direct
> i/o read"), an unaligned direct read past end of file would trigger EOF,
> since generic_file_aio_read detected this read-at-EOF condition and
> skipped the direct IO read entirely, returning 0. After that change, the
> read now reaches dio_generic, which detects the misalignment and returns
> EINVAL.
>
> This consolidates the generic direct-io to follow the same behavior of
> filesystems. Apparently, this fix will only affect ocfs2 since other
> filesystems do this verification before calling do_blockdev_direct_IO,
> with the exception of f2fs, which has the same bug, but is fixed in the
> next patch.
>
> it can be verified by a read loop on a file that does a partial read
> before EOF (On file that doesn't end at an aligned address). The
> following code fails on an unaligned file on filesystems without
> prior validation without this patch, but not on btrfs, ext4, and xfs.
>
> while (done < total) {
> ssize_t delta = pread(fd, buf + done, total - done, off + done);
> if (!delta)
> break;
> ...
> }
>
> Fix this regression by moving the misalignment check to after the EOF
> check added by commit 74cedf9b6c60 ("direct-io: Fix negative return from
> dio read beyond eof").
>
> Based on a patch by Jamie Liu.
>
> Reported-by: Jamie Liu <jamieliu@xxxxxxxxxx>
> Signed-off-by: Gabriel Krisman Bertazi <krisman@xxxxxxxxxxxxx>
This patch also looks good except for the fail_dio jump...
Honza
> ---
> fs/direct-io.c | 16 ++++++++--------
> 1 file changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/fs/direct-io.c b/fs/direct-io.c
> index 43460c8e0f90..01131a1674b8 100644
> --- a/fs/direct-io.c
> +++ b/fs/direct-io.c
> @@ -1165,14 +1165,6 @@ do_blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
> * the early prefetch in the caller enough time.
> */
>
> - if (align & blocksize_mask) {
> - if (bdev)
> - blkbits = blksize_bits(bdev_logical_block_size(bdev));
> - blocksize_mask = (1 << blkbits) - 1;
> - if (align & blocksize_mask)
> - return -EINVAL;
> - }
> -
> /* watch out for a 0 len io from a tricksy fs */
> if (iov_iter_rw(iter) == READ && !count)
> return 0;
> @@ -1200,6 +1192,14 @@ do_blockdev_direct_IO(struct kiocb *iocb, struct inode *inode,
> goto fail_dio;
> }
>
> + if (align & blocksize_mask) {
> + if (bdev)
> + blkbits = blksize_bits(bdev_logical_block_size(bdev));
> + blocksize_mask = (1 << blkbits) - 1;
> + if (align & blocksize_mask)
> + goto fail_dio;
> + }
> +
> if (dio->flags & DIO_LOCKING && iov_iter_rw(iter) == READ) {
> struct address_space *mapping = iocb->ki_filp->f_mapping;
>
> --
> 2.28.0
>
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
