linux-kernel - Re: pipe

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Message-ID: <20130311003530.GE21522@ZenIV.linux.org.uk>
Date:	Mon, 11 Mar 2013 00:35:31 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Dave Jones <davej@...hat.com>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: pipe_release oops.

On Sun, Mar 10, 2013 at 10:10:47PM +0000, Al Viro wrote:
> On Fri, Mar 08, 2013 at 10:30:01AM -0800, Linus Torvalds wrote:
> 
> > I must be missing something, and I wonder if the thing I'm missing is
> > that with OPEN_PATH we may now have open calls that don't actually
> > have FMODE_READ or FMODE_WRITE set at all.
> 
> With OPEN_PATH we don't call ->open() (or anything in the driver, for that
> matter) at all.  I really don't see how that could trigger...

Hmm...  How the devil would things like pipe_read_open() get called, anyway?
pipe_rdwr_open() can be called, all right - that happens if you do pipe()
and then open() via /proc/self/fd/<n>.  But how could pipe_read_open() and
pipe_write_open() be called?  They are accessible only as ->open() of
read_pipefifo_fops/write_pipefifo_fops.  And those are only used by
fifo_open(), which does reassign file->f_op to them, but does *not* call
their ->open()...
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