linux-kernel - Re: [PATCH -next] nbd: add the check to prevent overflow in __nbd

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Date:   Sat, 31 Jul 2021 08:57:44 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     Baokun Li <libaokun1@...wei.com>, josef@...icpanda.com,
        linux-block@...r.kernel.org, nbd@...er.debian.org,
        linux-kernel@...r.kernel.org
Cc:     patchwork@...wei.com, Hulk Robot <hulkci@...wei.com>
Subject: Re: [PATCH -next] nbd: add the check to prevent overflow in
 __nbd_ioctl()

On 7/30/21 7:48 PM, Baokun Li wrote:
> If user specify a large enough value of NBD blocks option, it may trigger
> signed integer overflow which may lead to nbd->config->bytesize becomes a
> large or small value, zero in particular.
> 
> UBSAN: Undefined behaviour in drivers/block/nbd.c:325:31
> signed integer overflow:
> 1024 * 4611686155866341414 cannot be represented in type 'long long int'
> [...]
> Call trace:
> [...]
>  handle_overflow+0x188/0x1dc lib/ubsan.c:192
>  __ubsan_handle_mul_overflow+0x34/0x44 lib/ubsan.c:213
>  nbd_size_set drivers/block/nbd.c:325 [inline]
>  __nbd_ioctl drivers/block/nbd.c:1342 [inline]
>  nbd_ioctl+0x998/0xa10 drivers/block/nbd.c:1395
>  __blkdev_driver_ioctl block/ioctl.c:311 [inline]
> [...]
> 
> Although it is not a big deal, still silence the UBSAN by limit
> the input value.
> 
> Reported-by: Hulk Robot <hulkci@...wei.com>
> Signed-off-by: Baokun Li <libaokun1@...wei.com>
> ---
>  drivers/block/nbd.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
> index c38317979f74..7c838bf8cc31 100644
> --- a/drivers/block/nbd.c
> +++ b/drivers/block/nbd.c
> @@ -1398,6 +1398,8 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
>  	case NBD_SET_SIZE:
>  		return nbd_set_size(nbd, arg, config->blksize);
>  	case NBD_SET_SIZE_BLOCKS:
> +		if (arg && (LLONG_MAX / arg <= config->blksize))
> +			return -EINVAL;

Use check_mul_overflow() instead?

-- 
Jens Axboe