linux-kernel - Re: ls -l /proc/1/exe -> Permission denied

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Message-ID: <OF94BC7D2A.31F0FF60-ONC1257D19.00528EC9-C1257D19.0052E7FB@transmode.se>
Date:	Fri, 18 Jul 2014 17:05:32 +0200
From:	Joakim Tjernlund <joakim.tjernlund@...nsmode.se>
To:	unlisted-recipients:; (no To-header on input)
Cc:	Richard Weinberger <richard.weinberger@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: ls -l /proc/1/exe -> Permission denied

Joakim Tjernlund/Transmode wrote on 2014/07/18 15:49:17:
> 
> Richard Weinberger <richard.weinberger@...il.com> wrote on 2014/07/18 
14:58:30:
> > 
> > On Thu, Jul 17, 2014 at 1:18 PM, Joakim Tjernlund
> > <joakim.tjernlund@...nsmode.se> wrote:
> > > Trying to real /proc/<pid>/exe I noticed I could not read links not
> > > belonging to my user such as:
> > > jocke >  ls -l /proc/1/exe
> > >              ls: cannot read symbolic link /proc/1/exe: Permission 
denied
> > >
> > > Is this expected?
> > 
> > Why do you think this is unexpected?

> It only shows the full path to the executable, compare with comm which 
shows basename(app).
> 
> I have an idea for qemu-user which needs to identify which processes
> are running /usr/bin/qemu-<arch> and which are not so it knows how
> to munge different /proc/ files.

Just to be clear, I expect to read where /proc/1/exe points, not the 
contents of the file
pointed to.

It seems that any and all symlinks are forbidden:
> ls -l /proc/1
ls: cannot read symbolic link /proc/1/cwd: Permission denied
ls: cannot read symbolic link /proc/1/root: Permission denied
ls: cannot read symbolic link /proc/1/exe: Permission denied

 Jocke
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