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

[Matthew Wilcox]

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?  ;-)

-- 
Intel are signing my paycheques ... these opinions are still mine
"Bill, look, we understand that you're interested in selling us this
operating system, but compare it to ours.  We can't possibly take such
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