linux-ext4 - Re: [PATCH] ext4: Fix offset overflow on 32-bit archs in ext4_iomap

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Date:   Fri, 23 Mar 2018 09:27:47 +0800
From:   Eryu Guan <guaneryu@...il.com>
To:     Jan Kara <jack@...e.cz>
Cc:     Ted Tso <tytso@....edu>, linux-ext4@...r.kernel.org,
        Jiri Slaby <jslaby@...e.cz>
Subject: Re: [PATCH] ext4: Fix offset overflow on 32-bit archs in
 ext4_iomap_begin()

On Tue, Feb 20, 2018 at 06:23:07PM +0100, Jan Kara wrote:
> From: Jiri Slaby <jslaby@...e.cz>
> 
> ext4_iomap_begin() has a bug where offset returned in the iomap
> structure will be truncated to unsigned long size. On 64-bit
> architectures this is fine but on 32-bit architectures obviously not.
> Not many places actually use the offset stored in the iomap structure
> but one of visible failures is in SEEK_HOLE / SEEK_DATA implementation.
> If we create a file like:
> 
> dd if=/dev/urandom of=file bs=1k seek=8m count=1
> 
> then
> 
> lseek64("file", 0x100000000ULL, SEEK_DATA)
> 
> wrongly returns 0x100000000 on unfixed kernel while it should return
> 0x200000000. Avoid the overflow by proper type cast.

It looks like a good candidate for a regression test in fstests :)

Thanks,
Eryu

> 
> Fixes: 545052e9e35a ("ext4: Switch to iomap for SEEK_HOLE / SEEK_DATA")
> Signed-off-by: Jiri Slaby <jslaby@...e.cz>
> Signed-off-by: Jan Kara <jack@...e.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 c94780075b04..c07d6456b548 100644
> --- a/fs/ext4/inode.c
> +++ b/fs/ext4/inode.c
> @@ -3524,7 +3524,7 @@ static int ext4_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
>  		iomap->flags |= IOMAP_F_DIRTY;
>  	iomap->bdev = inode->i_sb->s_bdev;
>  	iomap->dax_dev = sbi->s_daxdev;
> -	iomap->offset = first_block << blkbits;
> +	iomap->offset = (u64)first_block << blkbits;
>  	iomap->length = (u64)map.m_len << blkbits;
>  
>  	if (ret == 0) {
> -- 
> 2.13.6
>