linux-kernel - Re: [PATCH] checkpatch: warn for use of %px

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Date:   Mon, 04 Dec 2017 23:24:24 -0800
From:   Joe Perches <joe@...ches.com>
To:     "Tobin C. Harding" <me@...in.cc>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Andy Whitcroft <apw@...onical.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] checkpatch: warn for use of %px

On Tue, 2017-12-05 at 08:17 +1100, Tobin C. Harding wrote:
> Usage of the new %px specifier potentially leaks sensitive
> inforamtion. Printing kernel addresses exposes the kernel layout in

information

> memory, this is potentially exploitable. We have tools in the kernel to
> help us do the right thing. We can have checkpatch warn developers of
> potential dangers of using %px.
> 
> Have checkpatch emit a warning for usage of specifier %px.
> 
> Suggested-by: Andrew Morton <akpm@...ux-foundation.org>
> Signed-off-by: Tobin C. Harding <me@...in.cc>
> Co-Developed-by: Joe Perches <joe@...ches.com>
> 
> ---
> 
> Joe,
> 
> Are you happy with this tagging? Needs your signed-off-by still.

Maybe with a few corrections (below)
> 
> Andrew,
> 
> Is it okay to add your Suggested-by tag here?
> 
> I'm not entirely sure when one is supposed to add someones signed-off-by
> tag since the docs state that it should not be added without
> permission. I am also unsure where/when is the best time to request this
> permission.
[]
> diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
[]
> @@ -1612,6 +1612,17 @@ sub raw_line {
>  	return $line;
>  }
>  
> +sub stat_real {
> +	my ($linenr, $lc) = @_;
> +
> +	my $stat_real = raw_line($linenr, 0);
> +	for (my $count = $linenr + 1; $count <= $lc; $count++) {
> +		$stat_real = $stat_real . "\n" . raw_line($count, 0);
> +	}
> +
> +	return $stat_real;
> +}

If you are going to make a subroutine of this
there are some other places it could be used too.

> +
>  sub cat_vet {
>  	my ($vet) = @_;
>  	my ($res, $coded);
> @@ -5747,24 +5758,35 @@ sub process {
>  		    defined $stat &&
>  		    $stat =~ /^\+(?![^\{]*\{\s*).*\b(\w+)\s*\(.*$String\s*,/s &&
>  		    $1 !~ /^_*volatile_*$/) {
> -			my $bad_extension = "";
> +			my ($specifier, $extension, $stat_real);

My preference is not to define multiple variables on a single line.
I'd rather have:
			my $specifier;
			my $extension;
			my $stat_real;

> +			my $bad_specifier = "";
>  			my $lc = $stat =~ tr@\n@@;
>  			$lc = $lc + $linenr;
>  		        for (my $count = $linenr; $count <= $lc; $count++) {
>  				my $fmt = get_quoted_string($lines[$count - 1], raw_line($count, 0));
>  				$fmt =~ s/%%//g;
> -				if ($fmt =~ /(\%[\*\d\.]*p(?![\WFfSsBKRraEhMmIiUDdgVCbGNOx]).)/) {
> -					$bad_extension = $1;
> -					last;
> +
> +				while ($fmt =~ /(\%[\*\d\.]*p(\w))/g) {
> +					$specifier = $1;
> +					$extension = $2;
> +					if ($extension !~ /[FfSsBKRraEhMmIiUDdgVCbGNOx]/) {
> +						$bad_specifier = $specifier;
> +						last;
> +					}
> +					if ($extension eq "x" && !defined($stat_real)) {
> +						if (!defined($stat_real)) {
> +							$stat_real = stat_real($linenr, $lc);
> +						}
> +						WARN("VSPRINTF_SPECIFIER_PX",
> +						     "Using vsprintf specifier '\%px' potentially exposes the kernel layout in memory, if you don't _realy_ need the address please consider using '\%p'.\n" . "$here\n$stat_real\n");	

"kernel memory layout" not "kernel layout in memory"
"really" not "_realy_"