From: Yu Kuai <yukuai3@huawei.com>
To: <josef@toxicpanda.com>, <axboe@kernel.dk>, <paskripkin@gmail.com>
Cc: <linux-block@vger.kernel.org>, <nbd@other.debian.org>,
<linux-kernel@vger.kernel.org>, <yukuai3@huawei.com>,
<yi.zhang@huawei.com>, <luomeng12@huawei.com>
Subject: [PATCH 1/2] nbd: fix max value for 'first_minor'
Date: Thu, 21 Oct 2021 20:29:35 +0800 [thread overview]
Message-ID: <20211021122936.758221-2-yukuai3@huawei.com> (raw)
In-Reply-To: <20211021122936.758221-1-yukuai3@huawei.com>
commit b1a811633f73 ("block: nbd: add sanity check for first_minor")
checks that 'first_minor' should not be greater than 0xff, which is
wrong. Whitout the commit, the details that when user pass 0x100000,
it ends up create sysfs dir "/sys/block/43:0" are as follows:
nbd_dev_add
disk->first_minor = index << part_shift
-> default part_shift is 5, first_minor is 0x2000000
device_add_disk
ddev->devt = MKDEV(disk->major, disk->first_minor)
-> (0x2b << 20) | (0x2000000) = 0x2b00000
device_add
device_create_sys_dev_entry
format_dev_t
sprintf(buffer, "%u:%u", MAJOR(dev), MINOR(dev));
-> got 43:0
sysfs_create_link -> /sys/block/43:0
By the way, with the wrong fix, when part_shift is the default value,
only 8 ndb devices can be created since 8 << 5 is greater than 0xff.
Since the max bits for 'first_minor' should be the same as what
MKDEV() does, which is 20. Change the upper bound of 'first_minor'
from 0xff to 0xfffff.
Fixes: b1a811633f73 ("block: nbd: add sanity check for first_minor")
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 0d064fab6186..8f2c17a33c5b 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 first_minor will be truncated to
- * byte in __device_add_disk().
+ * sysfs files/links, since MKDEV() expect that the max bits of
+ * first_minor is 20.
*/
disk->first_minor = index << part_shift;
- if (disk->first_minor > 0xff) {
+ if (disk->first_minor > 0xfffff) {
err = -EINVAL;
goto out_free_idr;
}
--
2.31.1
next prev parent reply other threads:[~2021-10-21 12:16 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-21 12:29 [PATCH 0/2] nbd: fix sanity check for first_minor Yu Kuai
2021-10-21 12:29 ` Yu Kuai [this message]
2021-10-21 12:29 ` [PATCH 2/2] nbd: fix possible overflow for 'first_minor' in nbd_dev_add() Yu Kuai
2021-10-21 12:35 ` [PATCH 0/2] nbd: fix sanity check for first_minor Pavel Skripkin
2021-10-21 13:13 ` yukuai (C)
2021-10-21 13:37 ` yukuai (C)
2021-10-25 13:41 ` yukuai (C)
2021-11-01 8:06 ` yukuai (C)
2021-10-21 16:47 ` Pavel Skripkin
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