c_rehash: Do not use shell to invoke openssl

Except on VMS where it is safe.

This fixes CVE-2022-1292.

Reviewed-by: Paul Dale <pauli@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>

Author: t8m

tools/c_rehash.in

@@ -137,6 +137,23 @@ sub check_file {
 	return ($is_cert, $is_crl);
 }
 
+sub compute_hash {
+    my $fh;
+    if ( $^O eq "VMS" ) {
+        # VMS uses the open through shell
+        # The file names are safe there and list form is unsupported
+        if (!open($fh, "-|", join(' ', @_))) {
+            print STDERR "Cannot compute hash on '$fname'\n";
+            return;
+        }
+    } else {
+        if (!open($fh, "-|", @_)) {
+            print STDERR "Cannot compute hash on '$fname'\n";
+            return;
+        }
+    }
+    return (<$fh>, <$fh>);
+}
 
 # Link a certificate to its subject name hash value, each hash is of
 # the form <hash>.<n> where n is an integer. If the hash value already exists
@@ -146,10 +163,12 @@ sub check_file {
 
 sub link_hash_cert {
 		my $fname = $_[0];
-		$fname =~ s/'/'\\''/g;
-		my ($hash, $fprint) = `"$openssl" x509 $x509hash -fingerprint -noout -in "$fname"`;
+		my ($hash, $fprint) = compute_hash($openssl, "x509", $x509hash,
+						   "-fingerprint", "-noout",
+						   "-in", $fname);
 		chomp $hash;
 		chomp $fprint;
+		return if !$hash;
 		$fprint =~ s/^.*=//;
 		$fprint =~ tr/://d;
 		my $suffix = 0;
@@ -181,10 +200,12 @@ sub link_hash_cert {
 
 sub link_hash_crl {
 		my $fname = $_[0];
-		$fname =~ s/'/'\\''/g;
-		my ($hash, $fprint) = `"$openssl" crl $crlhash -fingerprint -noout -in '$fname'`;
+		my ($hash, $fprint) = compute_hash($openssl, "crl", $crlhash,
+						   "-fingerprint", "-noout",
+						   "-in", $fname);
 		chomp $hash;
 		chomp $fprint;
+		return if !$hash;
 		$fprint =~ s/^.*=//;
 		$fprint =~ tr/://d;
 		my $suffix = 0;