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

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Date:   Mon, 12 Nov 2018 11:17:29 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Christoph Hellwig <hch@...radead.org>,
        "Theodore Y. Ts'o" <tytso@....edu>, 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 12/11/2018 09:20, Christoph Hellwig wrote:
> On Sun, Nov 11, 2018 at 08:42:42AM -0500, Theodore Y. Ts'o wrote:
>> 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.
> 
> Well, that's what we have the security_file_ioctl() LSM hook for so that
> your security model can arbitrate access to ioctls.

Doesn't that have TOC-TOU races by design?

Also, what about SG_IO giving write access to files that are only opened
read-only (and only have read permissions)?

Paolo