[Linux-kernel-mentees] [RFC PATCH v2] checkpatch: add shebang check to EXECUTE_PERMISSIONS

[Ujjwal Kumar <ujjwalkumar0501@gmail.com>]

checkpatch.pl checks for invalid EXECUTE_PERMISSIONS on source
files. The script leverages filename extensions and its path in
the repository to decide whether to allow execute permissions on
the file or not.

Based on current check conditions, a perl script file having
execute permissions, without '.pl' extension in its filename
and not belonging to 'scripts/' directory is reported as ERROR
which is a false positive.

Adding a shebang check along with current conditions will make
the check more generalised and improve checkpatch reports.
To do so, without breaking the core design decision of checkpatch,
we can fetch the first line from the patch itself and match it for
a shebang pattern.

There can be cases where the first line is not part of the patch.
For instance: a patch that only changes permissions without
changing any of the file content.
In that case there may be a false positive report but in the end we
will have less false positives as we will be handling some of the
unhandled cases.

Signed-off-by: Ujjwal Kumar <ujjwalkumar0501@gmail.com>
---
Changes in v2:
  - Spelling correction and add example to commit
    message
  - Code style changes
  - Remove unncessary function argument
  - Use non-capturing group in regexp

 scripts/checkpatch.pl | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl
index fab38b493cef..7ebbee9c3672 100755
--- a/scripts/checkpatch.pl
+++ b/scripts/checkpatch.pl
@@ -1795,6 +1795,23 @@ sub get_stat_here {
 	return $herectx;
 }

+sub get_shebang {
+	my ($linenr) = @_;
+	my $rawline = "";
+	my $shebang = "";
+
+	$rawline = raw_line($linenr, 3);
+	if (defined($rawline) &&
+	    $rawline =~ /^\@\@ -\d+(?:,\d+)? \+(\d+)(,(\d+))? \@\@/) {
+		if (defined($1) && $1 == 1) {
+			$shebang = raw_line($linenr, 4);
+			$shebang = substr($shebang, 1);
+		}
+	}
+
+	return $shebang;
+}
+
 sub cat_vet {
 	my ($vet) = @_;
 	my ($res, $coded);
@@ -2680,7 +2697,9 @@ sub process {
 # Check for incorrect file permissions
 		if ($line =~ /^new (file )?mode.*[7531]\d{0,2}$/) {
 			my $permhere = $here . "FILE: $realfile\n";
+			my $shebang = get_shebang($linenr);
 			if ($realfile !~ m@scripts/@ &&
+			    $shebang !~ /^#!\s*(?:\/\w)+.*/ &&
 			    $realfile !~ /\.(py|pl|awk|sh)$/) {
 				ERROR("EXECUTE_PERMISSIONS",
 				      "do not set execute permissions for source files\n" . $permhere);

base-commit: 148fdf990dee4efd23c1114811b205de9c966680
--
2.26.2

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