linux-kernel - Re: [PATCH] block: allow IOC_PR_READ_* ioctls with BLK_OPEN

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Message-ID: <20260211154257.GA10237@lst.de>
Date: Wed, 11 Feb 2026 16:42:57 +0100
From: Christoph Hellwig <hch@....de>
To: Stefan Hajnoczi <stefanha@...hat.com>
Cc: Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org,
	linux-block@...r.kernel.org, Christoph Hellwig <hch@....de>,
	Martin Wilck <mwilck@...e.com>,
	Benjamin Marzinski <bmarzins@...hat.com>,
	Hannes Reinecke <hare@...e.de>
Subject: Re: [PATCH] block: allow IOC_PR_READ_* ioctls with BLK_OPEN_READ

On Tue, Feb 10, 2026 at 11:36:17AM -0500, Stefan Hajnoczi wrote:
> It is safe to reduce the permission requirement from BLK_OPEN_WRITE to
> BLK_OPEN_READ since these two ioctls do not modify the persistent
> reservation state. Userspace cannot use the information fetched by these
> ioctls to make changes to the device unless it later opens the device
> with BLK_OPEN_WRITE.

Hmm.  How often do we give unprivileged users access to the block
device node anyway?  But I guess if they can read all the data on
the device, they might as well see the reservation holders as well:

Reviewed-by: Christoph Hellwig <hch@....de>