linux-kernel - Re: [RFC] block: relax permission for Persistent Reservations ioctl

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Message-ID: <20230610060626.GA1595@lst.de>
Date:   Sat, 10 Jun 2023 08:06:26 +0200
From:   Christoph Hellwig <hch@....de>
To:     Jingbo Xu <jefflexu@...ux.alibaba.com>
Cc:     axboe@...nel.dk, hch@....de, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, tianjia.zhang@...ux.alibaba.com,
        xiang@...nel.org, casey@...aufler-ca.com
Subject: Re: [RFC] block: relax permission for Persistent Reservations ioctl

On Fri, Jun 09, 2023 at 06:21:22PM +0800, Jingbo Xu wrote:
> When the shared storage is accessed from containers [1], it's not
> recommended to grant CAP_SYS_ADMIN to containers for access to
> Persistent Reservations in risk of container escape.
> 
> Remove the extra CAP_SYS_ADMIN permission constraint for Persistent
> Reservations ioctl which shall do no harm [2].

I think we still to check that if CAP_SYS_ADMIN is not present,
the file descriptors needs to be open for write, and we're not called
on a partition (the latter should probbaly be always checked,
as a reservation for a partitions doesn't make sense).

But in general I think relaxing this is a good idea, we just need to
be very careful.  Looking at the discussion of unprivileged nvme
command passthrough might be a good start.