Subject: Re: [RFC] correct flags to f_mode conversion in __dentry_open
From: Eric Paris <eparis@redhat.com>
To: Al Viro <viro@ZenIV.linux.org.uk>
Cc: linux-kernel@vger.kernel.org, alan <alan@redhat.com>, aviro@redhat.com,
       drepper@redhat.com, hch@infradead.org, sds@tycho.nsa.gov,
       jmorris@namei.org
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	 <20080312183441.GJ27894@ZenIV.linux.org.uk>
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Date: Wed, 12 Mar 2008 14:41:00 -0400
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On Wed, 2008-03-12 at 18:34 +0000, Al Viro wrote:
> On Wed, Mar 12, 2008 at 02:25:27PM -0400, Eric Paris wrote:
> > I recently tried to add an SELinux BUG_ON in the case where the kernel
> > made a permission request for no permissions and was able to stumble
> > over it with something as simple as
> > 
> > open("/dev/null", 3);
> > 
> > Notice that 3 == (O_RDWR | O_WRONLY)
> > 
> > First question, is 3 ever a valid flag from from userspace to sys_open?
> 
> Yes.  "Check for both read and write permissions, set neither FMODE_READ
> nor FMODE_WRITE".
> 
> Don't break drivers, please - some use that for "ioctl-only" opens,
> with special semantics for those.

Ok, I'll just make SELinux happy allow the request if we don't have
FMODE_READ or FMODE_WRITE set.

-Eric

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