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

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Date:   Sat, 31 Jul 2021 09:48:54 +0800
From:   Baokun Li <libaokun1@...wei.com>
To:     <josef@...icpanda.com>, <axboe@...nel.dk>,
        <linux-block@...r.kernel.org>, <nbd@...er.debian.org>,
        <linux-kernel@...r.kernel.org>
CC:     <patchwork@...wei.com>, <libaokun1@...wei.com>,
        Hulk Robot <hulkci@...wei.com>
Subject: [PATCH -next] nbd: add the check to prevent overflow in __nbd_ioctl()

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;
 		return nbd_set_size(nbd, arg * config->blksize,
 				    config->blksize);
 	case NBD_SET_TIMEOUT:
-- 
2.31.1