Re: [PATCH] fat: check whether fs size exceeds device size

[OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>]

Zheng Lv <lv.zheng.2015@gmail.com> writes:

> The original code did not check for size of device. A truncated device
> would mount, I/O failures would occur when "attempt to access beyond end
> of device", leading to data lost.
>
> Fix this by comparing total-sectors field in BPB with size of device.
>
> This commit also prints a KERN_INFO message if there are extra sectors
> at end of device (ie. total sectors < device sectors).

[...]

> +	device_sectors = sb->s_bdev->bd_inode->i_size / logical_sector_size;
> +	if (device_sectors && total_sectors > device_sectors) {
> +		fat_msg(sb, KERN_ERR, "total sectors %u "
> +			"exceeds size of device (%llu sectors)",
> +			total_sectors, device_sectors);
> +		goto out_invalid;

Hm, it is a bit hard to think what to do. But I guess it is better to
allow access to rescue some files. (Yes, it may lost new data. But
read-only or in-place update is safe.)

> +	} else if (device_sectors && total_sectors < device_sectors) {
> +		fat_msg(sb, KERN_INFO, "%llu unused sectors at end of device",
> +			device_sectors - total_sectors);

This is legal setup. So, probably, should not pollute log for each mount.

> +	}
> +
>  	total_clusters = (total_sectors - sbi->data_start) / sbi->sec_per_clus;
>  
>  	if (sbi->fat_bits != 32)

-- 
OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>