linux-kernel - [PATCH 2/2] nbd: fix possible overflow for 'first_minor' in nbd_dev

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Message-ID: <20211021122936.758221-3-yukuai3@huawei.com>
Date:   Thu, 21 Oct 2021 20:29:36 +0800
From:   Yu Kuai <yukuai3@...wei.com>
To:     <josef@...icpanda.com>, <axboe@...nel.dk>, <paskripkin@...il.com>
CC:     <linux-block@...r.kernel.org>, <nbd@...er.debian.org>,
        <linux-kernel@...r.kernel.org>, <yukuai3@...wei.com>,
        <yi.zhang@...wei.com>, <luomeng12@...wei.com>
Subject: [PATCH 2/2] nbd: fix possible overflow for 'first_minor' in nbd_dev_add()

If 'part_shift' is not zero, then 'index << part_shift' might
overflow to a value that is not greater than '0xfffff', then sysfs
might complains about duplicate creation.

Fixes: b0d9111a2d53 ("nbd: use an idr to keep track of nbd devices")
Signed-off-by: Yu Kuai <yukuai3@...wei.com>
---
 drivers/block/nbd.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
index 8f2c17a33c5b..03a10a87500d 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -1808,11 +1808,11 @@ static struct nbd_device *nbd_dev_add(int index, unsigned int refs)
 	disk->major = NBD_MAJOR;
 
 	/* Too big first_minor can cause duplicate creation of
-	 * sysfs files/links, since MKDEV() expect that the max bits of
-	 * first_minor is 20.
+	 * sysfs files/links, since index << part_shift might overflow, or
+	 * MKDEV() expect that the max bits of first_minor is 20.
 	 */
 	disk->first_minor = index << part_shift;
-	if (disk->first_minor > 0xfffff) {
+	if (disk->first_minor < index || disk->first_minor > 0xfffff) {
 		err = -EINVAL;
 		goto out_free_idr;
 	}
-- 
2.31.1