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

[Tycho Andersen]

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@xxxxxxxx>
> ---
>  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