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Subject: Re: [PATCH] nbd: provide a way for userspace processes to identify
 device backends
To:     Prasanna Kumar Kalever <prasanna.kalever@redhat.com>,
        linux-kernel@vger.kernel.org
Cc:     linux-block@vger.kernel.org, nbd@other.debian.org,
        josef@toxicpanda.com, idryomov@redhat.com, xiubli@redhat.com
References: <20210429102828.31248-1-prasanna.kalever@redhat.com>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <f3035a3f-4494-929f-5c21-ba921a77ea6c@kernel.dk>
Date:   Wed, 16 Jun 2021 06:59:33 -0600
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On 4/29/21 4:28 AM, Prasanna Kumar Kalever wrote:
> Problem:
> On reconfigure of device, there is no way to defend if the backend
> storage is matching with the initial backend storage.
> 
> Say, if an initial connect request for backend "pool1/image1" got
> mapped to /dev/nbd0 and the userspace process is terminated. A next
> reconfigure request within NBD_ATTR_DEAD_CONN_TIMEOUT is allowed to
> use /dev/nbd0 for a different backend "pool1/image2"
> 
> For example, an operation like below could be dangerous:
> 
> $ sudo rbd-nbd map --try-netlink rbd-pool/ext4-image
> /dev/nbd0
> $ sudo blkid /dev/nbd0
> /dev/nbd0: UUID="bfc444b4-64b1-418f-8b36-6e0d170cfc04" TYPE="ext4"
> $ sudo pkill -9 rbd-nbd
> $ sudo rbd-nbd attach --try-netlink --device /dev/nbd0 rbd-pool/xfs-image
> /dev/nbd0
> $ sudo blkid /dev/nbd0
> /dev/nbd0: UUID="d29bf343-6570-4069-a9ea-2fa156ced908" TYPE="xfs"
> 
> Solution:
> Provide a way for userspace processes to keep some metadata to identify
> between the device and the backend, so that when a reconfigure request is
> made, we can compare and avoid such dangerous operations.
> 
> With this solution, as part of the initial connect request, backend
> path can be stored in the sysfs per device config, so that on a reconfigure
> request it's easy to check if the backend path matches with the initial
> connect backend path.
> 
> Please note, ioctl interface to nbd will not have these changes, as there
> won't be any reconfigure.

Applied, thanks.

-- 
Jens Axboe