linux-kernel - Re: [RFC PATCH] nvme: allow specific passthrough IOs without CAP

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Date:   Sun, 3 Oct 2021 12:29:22 +0300
From:   Sagi Grimberg <sagi@...mberg.me>
To:     Logan Gunthorpe <logang@...tatee.com>,
        Keith Busch <kbusch@...nel.org>, Jens Axboe <axboe@...com>,
        Christoph Hellwig <hch@....de>, linux-nvme@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Cc:     Stephen Bates <sbates@...thlin.com>,
        David Sloan <David.Sloan@...eticom.com>,
        Martin Oliveira <martin.oliveira@...eticom.com>,
        Kanchan Joshi <joshi.k@...sung.com>
Subject: Re: [RFC PATCH] nvme: allow specific passthrough IOs without
 CAP_SYSADMIN


> The passthrough IOCTL interface allows for prototyping new non-standard
> NVMe features in userspace. However, all passthrough commands require
> full CAP_SYSADMIN over and above file access to the device. This means
> applications must run as root when running proof of concepts which is
> not often desirable.
> 
> Instead, relax that requirement for vendor specific commands as well
> as identify and get_log_page admin commands (which both have vendor
> specific components). Identify and get_log_page only query information
> from the controller so users with this privilege shouldn't be able to
> cause any negative side effects and vendor specific commands are the
> vendors responsibility to avoid dangerous side effects.
> 
> Users that want to send any of these passthrough commands will still
> require access to the NVMe char device or namespace. Typically, the
> char device is only accessible by root anyway and namespaces are
> accessible by root and the disk group. Administrators are free to
> add udev rules to adjust these permissions for specific devices they
> want to allow.

I don't understand what is the difference between VS commands and normal
commands? Why do you consider VS commands safe to relax privileges as
opposed to any other command?