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From:   Ye Bin <yebin10@huawei.com>
To:     <josef@toxicpanda.com>, <axboe@kernel.dk>,
        <linux-block@vger.kernel.org>, <nbd@other.debian.org>
CC:     <linux-kernel@vger.kernel.org>, Yu Kuai <yukuai3@huawei.com>
Subject: [PATCH -next v4 2/4] nbd: fix possible overflow for 'first_minor' in nbd_dev_add()
Date:   Tue, 2 Nov 2021 09:52:35 +0800
Message-ID: <20211102015237.2309763-3-yebin10@huawei.com>
In-Reply-To: <20211102015237.2309763-1-yebin10@huawei.com>
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From: Yu Kuai <yukuai3@huawei.com>

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@huawei.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 678ee2688f63..cc32b5bc0f49 100644
--- a/drivers/block/nbd.c
+++ b/drivers/block/nbd.c
@@ -1803,11 +1803,11 @@ 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 > MINORMASK) {
+	if (disk->first_minor < index || disk->first_minor > MINORMASK) {
 		err = -EINVAL;
 		goto out_free_idr;
 	}
-- 
2.31.1