linux-kernel - [PATCH 3/4] checkpatch: warn for use of %px

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Message-Id: <1512689271-28051-4-git-send-email-me@tobin.cc>
Date:   Fri,  8 Dec 2017 10:27:50 +1100
From:   "Tobin C. Harding" <me@...in.cc>
To:     Joe Perches <joe@...ches.com>
Cc:     "Tobin C. Harding" <me@...in.cc>, linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andy Whitcroft <apw@...onical.com>
Subject: [PATCH 3/4] checkpatch: warn for use of %px

Usage of the new %px specifier potentially leaks sensitive
inforamtion. Printing kernel addresses exposes the kernel layout in
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.

Signed-off-by: Tobin C. Harding <me@...in.cc>
Co-Developed-by: Joe Perches <joe@...ches.com>
Acked-by: Joe Perches <joe@...ches.com>
---
 scripts/checkpatch.pl | 31 ++++++++++++++++++++++++-------
 1 file changed, 24 insertions(+), 7 deletions(-)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index 4534c9a9aefa..6df99d1ebca5 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -5750,21 +5750,38 @@ sub process {
 		    defined $stat &&
 		    $stat =~ /^\+(?![^\{]*\{\s*).*\b(\w+)\s*\(.*$String\s*,/s &&
 		    $1 !~ /^_*volatile_*$/) {
-			my $bad_extension = "";
+			my $specifier;
+			my $extension;
+			my $bad_specifier = "";
+			my $stat_real;
+
 			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)) {
+							$stat_real = get_stat_real($linenr, $lc);
+						}
+						WARN("VSPRINTF_SPECIFIER_PX",
+						     "Using vsprintf specifier '\%px' potentially exposes the kernel memory layout, if you don't really need the address please consider using '\%p'.\n" . "$here\n$stat_real\n");
+					}
 				}
+
 			}
-			if ($bad_extension ne "") {
-				my $stat_real = get_stat_real($linenr, $lc);
+			if ($bad_specifier ne "") {
+				$stat_real = get_stat_real($linenr, $lc);
 				WARN("VSPRINTF_POINTER_EXTENSION",
-				     "Invalid vsprintf pointer extension '$bad_extension'\n" . "$here\n$stat_real\n");
+				     "Invalid vsprintf pointer extension '$bad_specifier'\n" . "$here\n$stat_real\n");
 			}
 		}
 
-- 
2.7.4