linux-kernel - Re: [tpmdd-devel] [PATCH] TPM: Let the tpm char device be openable multiple times

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Message-ID: <20091104095814.13435621@lxorguk.ukuu.org.uk>
Date:	Wed, 4 Nov 2009 09:58:14 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Valdis.Kletnieks@...edu
Cc:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	Hal Finney <hal.finney@...il.com>,
	tpmdd-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
	srajiv@...ux.vnet.ibm.com
Subject: Re: [tpmdd-devel] [PATCH] TPM: Let the tpm char device be openable
 multiple times

> but those are hard-coded into the driver. But for the TPM, it's unclear if
> exclusive or non-exclusive is the right model. Maybe the right answer is to
> default to multiple opens, but have an ioctl() that turns on exclusive mode.
> If you have a 'tcsd' daemon, it will need to get launched early enough
> to do the open/ioctl before somebody else gets running anyhow, so it's
> not adding to any raciness.  Yeah, it's a hack. And there's still a small
> DoS issue - if the system is supposed to allow multiple opens, an abusive
> process can ioctl() it and break it.

What's wrong with "chmod" ?

BTW some drivers do also implement O_EXCL = one open semantics. It's not
exactly what POSIX expects but these are drivers and its a fairly logical
extension thereto.

Alan
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