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Date:   Mon, 12 Apr 2021 12:30:45 +0100
From:   Matthew Wilcox <willy@infradead.org>
To:     Jan Kara <jack@suse.cz>
Cc:     Ted Tso <tytso@mit.edu>, linux-ext4@vger.kernel.org,
        Eric Whitney <enwlinux@gmail.com>,
        linux-fsdevel@vger.kernel.org,
        "Darrick J . Wong" <djwong@kernel.org>
Subject: Re: [PATCH 3/3] ext4: Fix overflow in ext4_iomap_alloc()
Message-ID: <20210412113045.GI2531743@casper.infradead.org>
References: <20210412102333.2676-1-jack@suse.cz>
 <20210412102333.2676-4-jack@suse.cz>
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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
>