linux-kernel - Re: [PATCH] block/compat_ioctl: fix range check in BLKGETSIZE

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Date:   Sat, 9 Apr 2022 14:33:45 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Khazhismel Kumykov <khazhy@...gle.com>,
        Jens Axboe <axboe@...nel.dk>
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] block/compat_ioctl: fix range check in BLKGETSIZE

On 4/8/22 16:47, Khazhismel Kumykov wrote:
> kernel ulong and compat_ulong_t may not be same width. Use type directly
> to eliminate mismatches.
> 
> This would result in truncation rather than EFBIG for 32bit mode for
> large disks.
> 
> Signed-off-by: Khazhismel Kumykov <khazhy@...gle.com>
> ---
>   block/ioctl.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> Noticed this one was sitting in my "not landed yet" pile, third time's
> the charm? :)
> 
> diff --git a/block/ioctl.c b/block/ioctl.c
> index 4a86340133e4..959e93a90b29 100644
> --- a/block/ioctl.c
> +++ b/block/ioctl.c
> @@ -629,7 +629,7 @@ long compat_blkdev_ioctl(struct file *file, unsigned cmd, unsigned long arg)
>   		return compat_put_long(argp,
>   			(bdev->bd_disk->bdi->ra_pages * PAGE_SIZE) / 512);
>   	case BLKGETSIZE:
> -		if (bdev_nr_sectors(bdev) > ~0UL)
> +		if (bdev_nr_sectors(bdev) > ~((compat_ulong_t)0UL))
>   			return -EFBIG;
>   		return compat_put_ulong(argp, bdev_nr_sectors(bdev));

A nit: the "UL" and two parentheses can be left out. Anyway:

Reviewed-by: Bart Van Assche <bvanassche@....org>