Handle chauthtok with PAM_PRELIM_CHECK separately

If pam_sm_chauthtok is called with the flag PAM_PRELIM_CHECK set we
generate a separate call to the sssd to validate the old password before
asking for a new password and sending the change password request.

2 files changed, 37 insertions, 13 deletions

diff --git a/server/providers/krb5/krb5_auth.c b/server/providers/krb5/krb5_auth.c
index 4581278d..73018413 100644
--- a/server/providers/krb5/krb5_auth.c
+++ b/server/providers/krb5/krb5_auth.c
@@ -398,6 +398,7 @@ static struct krb5_ctx *get_krb5_ctx(struct be_req *be_req)
                                        struct krb5_ctx);
             break;
         case SSS_PAM_CHAUTHTOK:
+        case SSS_PAM_CHAUTHTOK_PRELIM:
             return talloc_get_type(be_req->be_ctx->bet_info[BET_CHPASS].pvt_bet_data,
                                        struct krb5_ctx);
             break;
@@ -685,14 +686,16 @@ void krb5_pam_handler(struct be_req *be_req)
 
     pd = talloc_get_type(be_req->req_data, struct pam_data);
 
-    if (pd->cmd != SSS_PAM_AUTHENTICATE && pd->cmd != SSS_PAM_CHAUTHTOK) {
+    if (pd->cmd != SSS_PAM_AUTHENTICATE && pd->cmd != SSS_PAM_CHAUTHTOK &&
+        pd->cmd != SSS_PAM_CHAUTHTOK_PRELIM) {
         DEBUG(4, ("krb5 does not handles pam task %d.\n", pd->cmd));
         pam_status = PAM_SUCCESS;
         dp_err = DP_ERR_OK;
         goto done;
     }
 
-    if (be_is_offline(be_req->be_ctx) && pd->cmd == SSS_PAM_CHAUTHTOK) {
+    if (be_is_offline(be_req->be_ctx) &&
+        (pd->cmd == SSS_PAM_CHAUTHTOK || pd->cmd == SSS_PAM_CHAUTHTOK_PRELIM)) {
         DEBUG(9, ("Password changes are not possible while offline.\n"));
         pam_status = PAM_AUTHINFO_UNAVAIL;
         dp_err = DP_ERR_OFFLINE;
@@ -958,6 +961,12 @@ static void krb5_child_done(struct tevent_req *req)
         pd->pam_status = *msg_status;
     }
 
+    if (*msg_status == PAM_SUCCESS && pd->cmd == SSS_PAM_CHAUTHTOK_PRELIM) {
+        pam_status = PAM_SUCCESS;
+        dp_err = DP_ERR_OK;
+        goto done;
+    }
+
     pref_len = strlen(CCACHE_ENV_NAME)+1;
     if (*msg_len > pref_len &&
         strncmp((const char *) &buf[p], CCACHE_ENV_NAME"=", pref_len) == 0) {
@@ -1047,6 +1056,7 @@ static void krb5_save_ccname_done(struct tevent_req *req)
 
         switch(pd->cmd) {
             case SSS_PAM_AUTHENTICATE:
+            case SSS_PAM_CHAUTHTOK_PRELIM:
                 password = talloc_size(be_req, pd->authtok_size + 1);
                 if (password != NULL) {
                     memcpy(password, pd->authtok, pd->authtok_size);
diff --git a/server/providers/krb5/krb5_child.c b/server/providers/krb5/krb5_child.c
index 2f485743..6eb420bc 100644
--- a/server/providers/krb5/krb5_child.c
+++ b/server/providers/krb5/krb5_child.c
@@ -299,19 +299,24 @@ static struct response *prepare_response_message(struct krb5_req *kr,
     }
 
     if (kerr == 0) {
-        if (kr->ccname == NULL) {
-            DEBUG(1, ("Error obtaining ccname.\n"));
-            return NULL;
-        }
+        if(kr->pd->cmd == SSS_PAM_CHAUTHTOK_PRELIM) {
+            ret = pack_response_packet(resp, PAM_SUCCESS, PAM_USER_INFO,
+                                       "success");
+        } else {
+            if (kr->ccname == NULL) {
+                DEBUG(1, ("Error obtaining ccname.\n"));
+                return NULL;
+            }
 
-        msg = talloc_asprintf(kr, "%s=%s",CCACHE_ENV_NAME, kr->ccname);
-        if (msg == NULL) {
-            DEBUG(1, ("talloc_asprintf failed.\n"));
-            return NULL;
-        }
+            msg = talloc_asprintf(kr, "%s=%s",CCACHE_ENV_NAME, kr->ccname);
+            if (msg == NULL) {
+                DEBUG(1, ("talloc_asprintf failed.\n"));
+                return NULL;
+            }
 
-        ret = pack_response_packet(resp, PAM_SUCCESS, PAM_ENV_ITEM, msg);
-        talloc_zfree(msg);
+            ret = pack_response_packet(resp, PAM_SUCCESS, PAM_ENV_ITEM, msg);
+            talloc_zfree(msg);
+        }
     } else {
         krb5_msg = sss_krb5_get_error_message(krb5_error_ctx, kerr);
         if (krb5_msg == NULL) {
@@ -528,6 +533,14 @@ static errno_t changepw_child(int fd, struct krb5_req *kr)
     talloc_zfree(pass_str);
     memset(kr->pd->authtok, 0, kr->pd->authtok_size);
 
+    if (kr->pd->cmd == SSS_PAM_CHAUTHTOK_PRELIM) {
+        DEBUG(9, ("Initial authentication for change password operation "
+                  "successfull.\n"));
+        krb5_free_cred_contents(kr->ctx, kr->creds);
+        pam_status = PAM_SUCCESS;
+        goto sendresponse;
+    }
+
     newpass_str = talloc_strndup(kr, (const char *) kr->pd->newauthtok,
                               kr->pd->newauthtok_size);
     if (newpass_str == NULL) {
@@ -824,6 +837,7 @@ static int krb5_setup(struct pam_data *pd, const char *user_princ_str,
             }
             break;
         case SSS_PAM_CHAUTHTOK:
+        case SSS_PAM_CHAUTHTOK_PRELIM:
             kr->child_req = changepw_child;
             break;
         default: