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

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Message-ID: <OFCEE18EFA.1A4893C0-ONC1257D1B.003DFC8D-C1257D1B.003E4142@transmode.se>
Date:	Sun, 20 Jul 2014 13:19:58 +0200
From:	Joakim Tjernlund <joakim.tjernlund@...nsmode.se>
To:	Richard Weinberger <richard.weinberger@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Andreas Schwab <schwab@...ux-m68k.org>
Subject: Re: ls -l /proc/1/exe -> Permission denied

Richard Weinberger <richard.weinberger@...il.com> wrote on 2014/07/20 
13:06:30:
> 
> On Sun, Jul 20, 2014 at 12:55 PM, Andreas Schwab <schwab@...ux-m68k.org> 
wrote:
> > Joakim Tjernlund <joakim.tjernlund@...nsmode.se> writes:
> >
> >> Andreas Schwab <schwab@...ux-m68k.org> wrote on 2014/07/19 22:21:59:
> >>>
> >>> Joakim Tjernlund <joakim.tjernlund@...nsmode.se> writes:
> >>>
> >>> > 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?
> >>>
> >>> Yes.  This information is considered private.
> >>
> >> I don't understand why though.
> >
> > It would allow bypassing access restrictions.
> 
> Do you have an example?
> I'm asking because an attacker could make any symlink as he wants to.
> A ln -s /etc/shadow lala still does not give me access to shadow...

precisely, I just want to see what it is pointing too.
Also, the links privs are inconsistent with current behaviour:
 lrwxrwxrwx   1 root root 0 Jul 15 19:03 exe

 Jocke
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