Re: [PATCH] block: fix an integer overflow in logical block size

From: Jens Axboe <axboe@kernel.dk>
To: Mikulas Patocka <mpatocka@redhat.com>
Cc: dm-devel@redhat.com, linux-block@vger.kernel.org,
	Mike Snitzer <msnitzer@redhat.com>
Subject: Re: [PATCH] block: fix an integer overflow in logical block size
Date: Wed, 15 Jan 2020 21:43:40 -0700	[thread overview]
Message-ID: <c013af2b-d5b9-06d9-e617-db882cde4a37@kernel.dk> (raw)
In-Reply-To: <alpine.LRH.2.02.2001150833180.31494@file01.intranet.prod.int.rdu2.redhat.com>

On 1/15/20 6:35 AM, Mikulas Patocka wrote:
> Logical block size has type unsigned short. That means that it can be at
> most 32768. However, there are architectures that can run with 64k pages
> (for example arm64) and on these architectures, it may be possible to
> create block devices with 64k block size.
> 
> For exmaple (run this on an architecture with 64k pages):
> # modprobe brd rd_size=1048576
> # dmsetup create cache --table "0 `blockdev --getsize /dev/ram0` writecache s /dev/ram0 /dev/ram1 65536 0"
> # mkfs.ext4 -b 65536 /dev/mapper/cache
> # mount -t ext4 /dev/mapper/cache /mnt/test
> 
> Mount will fail with this error because it tries to read the superblock using 2-sector
> access:
>   device-mapper: writecache: I/O is not aligned, sector 2, size 1024, block size 65536
>   EXT4-fs (dm-0): unable to read superblock
> 
> This patch changes the logical block size from unsigned short to unsigned
> int to avoid the overflow.

Thanks, applied.

-- 
Jens Axboe