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Date: Tue, 27 Feb 2018 17:29:50 +1100
From: "Tobin C. Harding" <me@...in.cc>
To: Tycho Andersen <tycho@...ho.ws>
Cc: Kernel Hardening <kernel-hardening@...ts.openwall.com>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/3] leaking_addresses: skip all /proc/PID except /proc/1
On Mon, Feb 26, 2018 at 10:09:31PM -0700, Tycho Andersen wrote:
> Hi Tobin,
>
> On Tue, Feb 27, 2018 at 03:45:09PM +1100, Tobin C. Harding wrote:
> > When the system is idle it is likely that most files under /proc/PID
> > will be identical for various processes. Scanning _all_ the PIDs under
> > /proc is unnecessary and implies that we are thoroughly scanning /proc.
> > This is _not_ the case because there may be ways userspace can trigger
> > creation of /proc files that leak addresses but were not present during
> > a scan. For these two reasons we should exclude all PID directories
> > under /proc except '1/'
> >
> > Exclude all /proc/PID except /proc/1.
> >
> > Signed-off-by: Tobin C. Harding <me@...in.cc>
> > ---
> > scripts/leaking_addresses.pl | 11 +++++++++++
> > 1 file changed, 11 insertions(+)
> >
> > diff --git a/scripts/leaking_addresses.pl b/scripts/leaking_addresses.pl
> > index 6e5bc57caeaa..fb40e2828f43 100755
> > --- a/scripts/leaking_addresses.pl
> > +++ b/scripts/leaking_addresses.pl
> > @@ -10,6 +10,14 @@
> > # Use --debug to output path before parsing, this is useful to find files that
> > # cause the script to choke.
> >
> > +#
> > +# When the system is idle it is likely that most files under /proc/PID will be
> > +# identical for various processes. Scanning _all_ the PIDs under /proc is
> > +# unnecessary and implies that we are thoroughly scanning /proc. This is _not_
> > +# the case because there may be ways userspace can trigger creation of /proc
> > +# files that leak addresses but were not present during a scan. For these two
> > +# reasons we exclude all PID directories under /proc except '1/'
> > +
> > use warnings;
> > use strict;
> > use POSIX;
> > @@ -472,6 +480,9 @@ sub walk
> > my $path = "$pwd/$file";
> > next if (-l $path);
> >
> > + # skip /proc/PID except /proc/1
> > + next if ($path =~ /\/proc\/(?:[2-9][0-9]*|1[0-9]+)/);
>
> Can't we just do,
>
> substr($path, 0, len("/proc/1/")) eq "/proc/1/" ?
>
> seems much easier to read than the regex.
This is much better. I guess it's true what they say, be careful after
reading a book about hammers, everything will look like a nail.
Tobin
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