diff mbox series

[v2,3/3] direct-io: defer alignment check until after the EOF check

Message ID 20200903200414.673105-4-krisman@collabora.com (mailing list archive)
State New, archived
Headers show
Series Unaligned DIO read error path fix and clean ups | expand

Commit Message

Gabriel Krisman Bertazi Sept. 3, 2020, 8:04 p.m. UTC
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@google.com>
Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
---
 fs/direct-io.c | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

Comments

Jan Kara Sept. 4, 2020, 7:49 a.m. UTC | #1
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@google.com>
> Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>

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
>
diff mbox series

Patch

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;