passwd(1) - use explicit_bzero(3)

[Gleydson Soares]

after recents passwd(1) changes, We should use explicit_bzero(3) for
clearing these sensitive strings.
OK?

Index: local_passwd.c
===================================================================
RCS file: /cvs/src/usr.bin/passwd/local_passwd.c,v
retrieving revision 1.50
diff -u -p -r1.50 local_passwd.c
--- local_passwd.c      31 Aug 2016 12:41:19 -0000      1.50
+++ local_passwd.c      31 Aug 2016 14:17:40 -0000
@@ -174,8 +174,10 @@ getnewpasswd(struct passwd *pw, login_ca
                        }
                        if (crypt_checkpass(p, pw->pw_passwd) != 0) {
                                errno = EACCES;
+                               explicit_bzero(oldpass, sizeof(oldpass));
                                pw_error(NULL, 1, 1);
                        }
+                       explicit_bzero(oldpass, sizeof(oldpass));
                }
        }
 
@@ -204,6 +206,7 @@ getnewpasswd(struct passwd *pw, login_ca
                if (p != NULL && strcmp(newpass, p) == 0)
                        break;
                (void)printf("Mismatch; try again, EOF to quit.\n");
+               explicit_bzero(newpass, sizeof(newpass));
        }
 
        (void)signal(SIGINT, saveint);
@@ -212,8 +215,10 @@ getnewpasswd(struct passwd *pw, login_ca
        pref = login_getcapstr(lc, "localcipher", NULL, NULL);
        if (crypt_newhash(newpass, pref, hash, sizeof(hash)) != 0) {
                (void)printf("Couldn't generate hash.\n");
+               explicit_bzero(newpass, sizeof(newpass));
                pw_error(NULL, 0, 0);
        }
+       explicit_bzero(newpass, sizeof(newpass));
        free(pref);
        return hash;
 }