do not call dp callbacks when responder is shutting down

https://fedorahosted.org/sssd/ticket/1514

We were experiencing crash duting responder shut down. This happened
when there were some unresolved dp request during the shut down.

The memory hierarchy is main_ctx->specific_ctx->rctx, where
specific_ctx may be one of the pam, nss, sudo, etc. contexts.

If we try to call dp request callback as a result of responder
termination, the specific context is already semi freed, which may
cause crash.

3 files changed, 25 insertions, 0 deletions

diff --git a/src/responder/common/responder.h b/src/responder/common/responder.h
index 5bab0d3c3..2903aac00 100644
--- a/src/responder/common/responder.h
+++ b/src/responder/common/responder.h
@@ -104,6 +104,8 @@ struct resp_ctx {
     char *default_domain;
 
     void *pvt_ctx;
+
+    bool shutting_down;
 };
 
 struct cli_ctx {
diff --git a/src/responder/common/responder_common.c b/src/responder/common/responder_common.c
index 4fa819097..d9f73fe26 100644
--- a/src/responder/common/responder_common.c
+++ b/src/responder/common/responder_common.c
@@ -716,6 +716,18 @@ failed:
     return EIO;
 }
 
+static int sss_responder_ctx_destructor(void *ptr)
+{
+    struct resp_ctx *rctx = talloc_get_type(ptr, struct resp_ctx);
+
+    /* mark that we are shutting down the responder, so it is propagated
+     * into underlying contexts that are freed right before rctx */
+    DEBUG(SSSDBG_TRACE_FUNC, ("Responder is being shut down\n"));
+    rctx->shutting_down = true;
+
+    return 0;
+}
+
 int sss_process_init(TALLOC_CTX *mem_ctx,
                      struct tevent_context *ev,
                      struct confdb_ctx *cdb,
@@ -745,6 +757,9 @@ int sss_process_init(TALLOC_CTX *mem_ctx,
     rctx->sock_name = sss_pipe_name;
     rctx->priv_sock_name = sss_priv_pipe_name;
     rctx->confdb_service_path = confdb_service_path;
+    rctx->shutting_down = false;
+
+    talloc_set_destructor((TALLOC_CTX*)rctx, sss_responder_ctx_destructor);
 
     ret = confdb_get_int(rctx->cdb, rctx->confdb_service_path,
                          CONFDB_RESPONDER_CLI_IDLE_TIMEOUT,
diff --git a/src/responder/common/responder_dp.c b/src/responder/common/responder_dp.c
index ca9cb834d..34fc9f349 100644
--- a/src/responder/common/responder_dp.c
+++ b/src/responder/common/responder_dp.c
@@ -76,6 +76,14 @@ static int sss_dp_req_destructor(void *ptr)
         sdp_req->pending_reply = NULL;
     }
 
+    /* Do not call callbacks if the responder is shutting down, because
+     * the top level responder context (pam_ctx, sudo_ctx, ...) may be
+     * already semi-freed and we may end up accessing freed memory.
+     */
+    if (sdp_req->rctx->shutting_down) {
+        return 0;
+    }
+
     /* If there are callbacks that haven't been invoked, return
      * an error now.
      */