nsswitch: fix crash on null pam change pw response

The function _pam_winbind_change_pwd crashes due to a null value passed
to the function strcasecmp and denies to login via graphical login
manager. Check for a null value before doing a strcasecmp.

Bug-Ubuntu: https://bugs.launchpad.net/bugs/1003296
Bug: https://bugzilla.samba.org/show_bug.cgi?id=9013
(Desktop Managers (xdm, gdm, lightdm...) crashes with SIGSEGV in
_pam_winbind_change_pwd() when password is expiring)
(cherry picked from commit 47f2211f137688a7c46c4a38571a9f94e59dbf6a)

diff --git a/nsswitch/pam_winbind.c b/nsswitch/pam_winbind.c
index 81055c9f0ff9461ce30cc4cb420f9b72937ee5d2..fdaf8074fcf6a6caf648f49b755e6b7d6723d7ff 100644 (file)
--- a/nsswitch/pam_winbind.c
+++ b/nsswitch/pam_winbind.c
@@ -831,7 +831,7 @@ static bool _pam_winbind_change_pwd(struct pwb_context *ctx)
        }
        _pam_log(ctx, LOG_CRIT, "Received [%s] reply from application.\n", resp->resp);
 
-       if (strcasecmp(resp->resp, "yes") == 0) {
+       if ((resp->resp != NULL) && (strcasecmp(resp->resp, "yes") == 0)) {
                retval = true;
        }