linux-kernel - Re: [Bugme-new] [Bug 10284] New: executables with read bit 'off' cannot open /dev/stdin

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Message-ID: <20080319222808.GF424@parisc-linux.org>
Date:	Wed, 19 Mar 2008 16:28:08 -0600
From:	Matthew Wilcox <matthew@....cx>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	bugme-daemon@...zilla.kernel.org, joe@...itfly.org
Subject: Re: [Bugme-new] [Bug 10284] New: executables with read bit 'off' cannot open /dev/stdin

On Wed, Mar 19, 2008 at 02:31:08PM -0700, Andrew Morton wrote:
> > Problem Description: if the read bit of a binary executable is off, then open()
> > on /dev/stdin fails with a EACCES error.
> 
> This is, umm, unexpected?

I'm not sure it's unexpected.  It's undesirable, certainly.

> > open("/dev/stdin", O_RDONLY)            = -1 EACCES (Permission denied)
> > 
> > The last line shows a Permission denied error on opening /dev/stdin. If a
> > normal filesystem (i.e. not-/dev/) filename is used, the open works normally.
> > 
> > I have reproduced this on 2.4 and 2.6 kernels
> > Just a guess here: is an error flag from attempting to read the binary not
> > getting cleared and is being reported when trying to open stdin?

I think the guess is faulty.  Could you show ls -l /dev/stdin ?  On my
system, it reports:

lrwxrwxrwx 1 root root 15 2008-03-10 11:03 /dev/stdin -> /proc/self/fd/0

Wild guess: Users can't access /proc/ directories of executables with the
read-bit clear in order to prevent users from reading the state anyway.

I wonder how effective clearing the read-bit is these days.
Don't we all have source to all the applications anyway?  ;-)

-- 
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