git-cvsserver: protect against NULL in crypt(3)

Some versions of crypt(3) will return NULL when passed an unsupported
hash type (ex: OpenBSD with DES), so check for undef instead of using
it directly.

Also use this to probe the system and select a better hash function in
the tests, so it can pass successfully.

Signed-off-by: Carlo Marcelo Arenas Belón <carenas@gmail.com>
[jc: <CAPUEspjqD5zy8TLuFA96usU7FYi=0wF84y7NgOVFqegtxL9zbw@mail.gmail.com>]
Signed-off-by: Junio C Hamano <gitster@pobox.com>

git-cvsserver.perl

@@ -222,10 +222,11 @@ if ($state->{method} eq 'pserver') {
         open my $passwd, "<", $authdb or die $!;
         while (<$passwd>) {
             if (m{^\Q$user\E:(.*)}) {
-                if (crypt(descramble($password), $1) eq $1) {
+                my $hash = crypt(descramble($password), $1);
+                if (defined $hash and $hash eq $1) {
                     $auth_ok = 1;
                 }
-            };
+            }
         }
         close $passwd;
 

t/t9400-git-cvsserver-server.sh

@@ -36,7 +36,12 @@ CVSWORK="$PWD/cvswork"
 CVS_SERVER=git-cvsserver
 export CVSROOT CVS_SERVER
 
-PWDHASH='lac2ItudM3.KM'
+if perl -e 'exit(1) if not defined crypt("", "cv")'
+then
+	PWDHASH='lac2ItudM3.KM'
+else
+	PWDHASH='$2b$10$t8fGvE/a9eLmfOLzsZme2uOa2QtoMYwIxq9wZA6aBKtF1Yb7FJIzi'
+fi
 
 rm -rf "$CVSWORK" "$SERVERDIR"
 test_expect_success 'setup' '