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    SubjectRe: [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@tobin.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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