Open the PAC socket from krb5_child before dropping root

The PAC responder by default allows only connections from the root user.
This patch opens the socket to the PAC responder before the krb5_child
drops privileges so the connection seemingly comes from root.

https://fedorahosted.org/sssd/ticket/2559

Reviewed-by: Sumit Bose <sbose@redhat.com>
(cherry picked from commit 858e750c3d4fe54e50616a1ed1e101469503c070)

3 files changed, 27 insertions, 0 deletions

diff --git a/src/providers/krb5/krb5_child.c b/src/providers/krb5/krb5_child.c
index 39cd62846..4c2f81fb1 100644
--- a/src/providers/krb5/krb5_child.c
+++ b/src/providers/krb5/krb5_child.c
@@ -2305,6 +2305,14 @@ static krb5_error_code privileged_krb5_setup(struct krb5_req *kr,
         }
     }
 
+    if (kr->send_pac) {
+        ret = sss_pac_check_and_open();
+        if (ret != EOK) {
+            DEBUG(SSSDBG_MINOR_FAILURE, "Cannot open the PAC responder socket\n");
+            /* Not fatal */
+        }
+    }
+
     return 0;
 }
 
diff --git a/src/sss_client/common.c b/src/sss_client/common.c
index 7c4bb7ab8..1b0fb1223 100644
--- a/src/sss_client/common.c
+++ b/src/sss_client/common.c
@@ -749,6 +749,19 @@ enum nss_status sss_nss_make_request(enum sss_cli_command cmd,
     }
 }
 
+int sss_pac_check_and_open(void)
+{
+    enum sss_status ret;
+    int errnop;
+
+    ret = sss_cli_check_socket(&errnop, SSS_PAC_SOCKET_NAME);
+    if (ret != SSS_STATUS_SUCCESS) {
+        return EIO;
+    }
+
+    return EOK;
+}
+
 int sss_pac_make_request(enum sss_cli_command cmd,
                          struct sss_cli_req_data *rd,
                          uint8_t **repbuf, size_t *replen,
diff --git a/src/sss_client/sss_cli.h b/src/sss_client/sss_cli.h
index 2d909311c..6286077fc 100644
--- a/src/sss_client/sss_cli.h
+++ b/src/sss_client/sss_cli.h
@@ -511,6 +511,12 @@ int sss_pam_make_request(enum sss_cli_command cmd,
                          int *errnop);
 void sss_pam_close_fd(void);
 
+/* Checks access to the PAC responder and opens the socket, if available.
+ * Required for processes like krb5_child that need to open the socket
+ * before dropping privs.
+ */
+int sss_pac_check_and_open(void);
+
 int sss_pac_make_request(enum sss_cli_command cmd,
                          struct sss_cli_req_data *rd,
                          uint8_t **repbuf, size_t *replen,