linux-kernel - Re: [PATCH 1/3] leaking_addresses: skip all /proc/PID except /proc/1

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Message-ID: <20180301210623.GA15198@eros>
Date:   Fri, 2 Mar 2018 08:06:23 +1100
From:   "Tobin C. Harding" <me@...in.cc>
To:     Kernel Hardening <kernel-hardening@...ts.openwall.com>
Cc:     Tycho Andersen <tycho@...ho.ws>,
        LKML <linux-kernel@...r.kernel.org>,
        Alexander Kapshuk <alexander.kapshuk@...il.com>
Subject: Re: [PATCH 1/3] leaking_addresses: skip all /proc/PID except /proc/1

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]+)/);

Perhaps the intent of this is clearer?

			next if (($path =~ /^\/proc\/[0-9]+$/) &&
			     	 ($path !~ /^\/proc\/1$/));


thanks,
Tobin.