[3/3] ext4: Fix overflow in ext4_iomap_alloc()

A code in iomap alloc may overblock block number when converting it to
byte offset. Luckily this is mostly harmless as we will just use more
expensive method of writing using unwritten extents even though we are
writing beyond i_size.

Fixes: 378f32bab371 ("ext4: introduce direct I/O write using iomap infrastructure")
Signed-off-by: Jan Kara <jack@suse.cz>
---
 fs/ext4/inode.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

On Mon, Apr 12, 2021 at 12:23:33PM +0200, Jan Kara wrote:
> A code in iomap alloc may overblock block number when converting it to

"overflow"?

> byte offset. Luckily this is mostly harmless as we will just use more
> expensive method of writing using unwritten extents even though we are
> writing beyond i_size.
> 
> Fixes: 378f32bab371 ("ext4: introduce direct I/O write using iomap infrastructure")
> Signed-off-by: Jan Kara <jack@suse.cz>
> ---
>  fs/ext4/inode.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
> index 0948a43f1b3d..7cebbb2d2e34 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3420,7 +3420,7 @@ static int ext4_iomap_alloc(struct inode *inode, struct ext4_map_blocks *map,
>  	 * i_disksize out to i_size. This could be beyond where direct I/O is
>  	 * happening and thus expose allocated blocks to direct I/O reads.
>  	 */
> -	else if ((map->m_lblk * (1 << blkbits)) >= i_size_read(inode))
> +	else if (((loff_t)map->m_lblk << blkbits) >= i_size_read(inode))
>  		m_flags = EXT4_GET_BLOCKS_CREATE;
>  	else if (ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))
>  		m_flags = EXT4_GET_BLOCKS_IO_CREATE_EXT;
> -- 
> 2.26.2
>

On Mon, Apr 12, 2021 at 12:23:33PM +0200, Jan Kara wrote:
> A code in iomap alloc may overblock block number when converting it to
> byte offset. Luckily this is mostly harmless as we will just use more
> expensive method of writing using unwritten extents even though we are
> writing beyond i_size.
> 
> Fixes: 378f32bab371 ("ext4: introduce direct I/O write using iomap infrastructure")
> Signed-off-by: Jan Kara <jack@suse.cz>

This was part of the patch series "ext4: Fix data corruption when
extending DIO write races with buffered read" but which fixes an
unrelated problem.  The patch series was dropped in favor of a
different approach, but it looks like this patch is still applicable,
so I've applied with a minor typo fix in the commit description.

   		       	     	      - Ted