linux-kernel - Re: [PATCH -next v3] nbd: add the check to prevent overflow in __nbd

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Message-ID: <49104529-74e4-27ed-945f-75e04c1b5968@toxicpanda.com>
Date:   Fri, 13 Aug 2021 11:53:48 -0400
From:   Josef Bacik <josef@...icpanda.com>
To:     Baokun Li <libaokun1@...wei.com>, axboe@...nel.dk,
        linux-block@...r.kernel.org, nbd@...er.debian.org,
        linux-kernel@...r.kernel.org
Cc:     patchwork@...wei.com, yukuai3@...wei.com,
        Hulk Robot <hulkci@...wei.com>
Subject: Re: [PATCH -next v3] nbd: add the check to prevent overflow in
 __nbd_ioctl()

On 8/3/21 10:12 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>
> ---
> V1->V2:
> 	Use check_mul_overflow().
> V2->V3:
> 	The check_mul_overflow function requires the same input parameter type.
> 
>   drivers/block/nbd.c | 8 ++++++--
>   1 file changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
> index c38317979f74..5a42b838d26c 100644
> --- a/drivers/block/nbd.c
> +++ b/drivers/block/nbd.c
> @@ -1384,6 +1384,7 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
>   		       unsigned int cmd, unsigned long arg)
>   {
>   	struct nbd_config *config = nbd->config;
> +	loff_t bytesize;
>   
>   	switch (cmd) {
>   	case NBD_DISCONNECT:
> @@ -1398,8 +1399,11 @@ 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:
> -		return nbd_set_size(nbd, arg * config->blksize,
> -				    config->blksize);
> +		if (unlikely(check_mul_overflow((loff_t)arg,
> +						config->blksize,
> +						&bytesize)))
> +			return -EINVAL;
> +		return nbd_set_size(nbd, bytesize, config->blksize);

The unlikely isn't needed here, just makes it harder to read the thing, drop it 
and then you can add

Reviewed-by: Josef Bacik <josef@...icpanda.com>

Thanks,

Josef