linux-kernel - Re: [RFC] correct flags to f_mode conversion in __dentry

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Date:	Sat, 15 Mar 2008 18:00:58 -0400
From:	Alexander Viro <aviro@...hat.com>
To:	Alan Cox <alan@...hat.com>
Cc:	Eric Paris <eparis@...hat.com>, linux-kernel@...r.kernel.org,
	aviro@...hat.com, drepper@...hat.com, hch@...radead.org,
	sds@...ho.nsa.gov, jmorris@...ei.org
Subject: Re: [RFC] correct flags to f_mode conversion in __dentry_open

On Sat, Mar 15, 2008 at 05:59:52PM -0400, Alan Cox 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.
> 
> > does 11 really mean and should it really always be mapped to (FMODE_READ
> > | FMODE_WRITE) or should it continue to get mapped to 'no permission?'
> 
> We've always mapped 3 to "no permission" to read or write. It's a linuxism

Note that we *do* request MAY_READ|MAY_WRITE; "no permission" part is
about what you can do to resulting descriptor afterwards.
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