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Message-ID: <20180227050931.4h64hkxglv3ekzsp@cisco>
Date: Mon, 26 Feb 2018 22:09:31 -0700
From: Tycho Andersen <tycho@...ho.ws>
To: "Tobin C. Harding" <me@...in.cc>
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
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.
Cheers,
Tycho
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