linux-kernel - Re: [PATCH 0/3] SG_IO command filtering via sysfs

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Date:   Sun, 11 Nov 2018 08:42:42 -0500
From:   "Theodore Y. Ts'o" <tytso@....edu>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
        linux-scsi@...r.kernel.org, Hannes Reinecke <hare@...e.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        James Bottomley <James.Bottomley@...senpartnership.com>
Subject: Re: [PATCH 0/3] SG_IO command filtering via sysfs

On Sun, Nov 11, 2018 at 05:14:45AM -0800, Christoph Hellwig wrote:
> I think this goes in the wrong way.  There isn't really any point
> in filtering at all if we have access to the whole device by the
> file persmissions, and we generally should not allow any access for
> partitions.

It really depends on the security model being used on a particular
system.  I can easily imagine scenarios where userspace is allowed
full access to the device with respect to read/write/open, but the
security model doesn't want to allow access to various SCSI commands
such as firmware upload commands, TCG commads, the
soon-to-be-standardized Zone Activation Commands (which allow dynamic
conversion of HDD recording modes between CMR and SMR), etc.

And this is before we get to crazy container / namespace scenarios.
And *no*, let's not have a SG_IO namespace!  :-)

> I think we need to simplify the selection, not add crazy amounts of
> special case code.

I have the opposite opinions in terms of wanting more complex
filtering rules, but I also agree that special case C code is not the
answer --- and why I suggested that eBPF filtering rules is the right
way to go.

					- Ted