source4 smbd: remove global control pipe from process_standard.

The standard model uses a pipe to signal the worker processes spawned on
accept that the controlling process has terminated and that they should
shut down.  This pipe is currently a static global variable in
process_standard.c.

This patch replaces that global pipe with a file descriptor passed into
the process model init functions, giving  a single mechanism across all process
models.  This paves the way for the addition of a pre-fork process model.

Ensuring that the correct file descriptors are closed, is difficult so
it is best do this only once rather than require the process models to
do this individually.

Notes on debugging pipe ownership:

Add code to log the process id and the file descriptor of the writeable
pipe.

run:
   lsof | grep FIFO | grep samba | grep <process id>
   this will produce lines like:

   samba 25624 him 4w FIFO 0,10 0t0 472206 pipe

   where: 4w is the file descriptor and mode and the number to the left
          of "pipe" is the pipe id.
then:
   lsof | grep FIFO | grep samba | grep <pipe id>

   This will display all the processes with the pipe open and the mode
   only the smbd master process should have it open in write mode.

Signed-off-by: Gary Lockyer <gary@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Ralph Boehme <slow@samba.org>

Autobuild-User(master): Ralph Böhme <slow@samba.org>
Autobuild-Date(master): Thu Sep 28 02:08:34 CEST 2017 on sn-devel-144

6 files changed, 97 insertions, 42 deletions

diff --git a/source4/smbd/process_model.h b/source4/smbd/process_model.h
index 4399d3689fb..d7bf3c87c7b 100644
--- a/source4/smbd/process_model.h
+++ b/source4/smbd/process_model.h
@@ -61,7 +61,8 @@ struct model_ops {
 			 void (*)(struct tevent_context *, 
 				  struct loadparm_context *, struct server_id, 
 				  void *),
-			 void *);
+			 void *,
+			 int);
 
 	/* function to terminate a connection or task */
 	void (*terminate)(struct tevent_context *, struct loadparm_context *lp_ctx,
diff --git a/source4/smbd/process_single.c b/source4/smbd/process_single.c
index f483e000be7..54169e9b0cc 100644
--- a/source4/smbd/process_single.c
+++ b/source4/smbd/process_single.c
@@ -85,11 +85,12 @@ static void single_accept_connection(struct tevent_context *ev,
 /*
   called to startup a new task
 */
-static void single_new_task(struct tevent_context *ev, 
+static void single_new_task(struct tevent_context *ev,
 			    struct loadparm_context *lp_ctx,
 			    const char *service_name,
-			    void (*new_task)(struct tevent_context *, struct loadparm_context *, struct server_id, void *), 
-			    void *private_data)
+			    void (*new_task)(struct tevent_context *, struct loadparm_context *, struct server_id, void *),
+			    void *private_data,
+			    int from_parent_fd)
 {
 	pid_t pid = getpid();
 	/* start our taskids at MAX_INT32, the first 2^31 tasks are is reserved for fd numbers */
diff --git a/source4/smbd/process_standard.c b/source4/smbd/process_standard.c
index 8d962d55130..c6cbfc23eda 100644
--- a/source4/smbd/process_standard.c
+++ b/source4/smbd/process_standard.c
@@ -42,22 +42,13 @@ struct standard_child_state {
 
 NTSTATUS process_model_standard_init(TALLOC_CTX *);
 
-/* we hold a pipe open in the parent, and the any child
-   processes wait for EOF on that pipe. This ensures that
-   children die when the parent dies */
-static int child_pipe[2] = { -1, -1 };
+static int from_parent_fd;
 
 /*
   called when the process model is selected
 */
 static void standard_model_init(void)
 {
-	int rc;
-
-	rc = pipe(child_pipe);
-	if (rc < 0) {
-		smb_panic("Failed to initialize pipe!");
-	}
 }
 
 static void sighup_signal_handler(struct tevent_context *ev,
@@ -312,17 +303,12 @@ static void standard_accept_connection(struct tevent_context *ev,
 		smb_panic("Failed to re-initialise imessaging after fork");
 	}
 
-	fde = tevent_add_fd(ev, ev, child_pipe[0], TEVENT_FD_READ,
+	fde = tevent_add_fd(ev, ev, from_parent_fd, TEVENT_FD_READ,
 		      standard_pipe_handler, NULL);
 	if (fde == NULL) {
 		smb_panic("Failed to add fd handler after fork");
 	}
 
-	if (child_pipe[1] != -1) {
-		close(child_pipe[1]);
-		child_pipe[1] = -1;
-	}
-
 	se = tevent_add_signal(ev,
 				ev,
 				SIGHUP,
@@ -368,11 +354,12 @@ static void standard_accept_connection(struct tevent_context *ev,
 /*
   called to create a new server task
 */
-static void standard_new_task(struct tevent_context *ev, 
+static void standard_new_task(struct tevent_context *ev,
 			      struct loadparm_context *lp_ctx,
 			      const char *service_name,
 			      void (*new_task)(struct tevent_context *, struct loadparm_context *lp_ctx, struct server_id , void *),
-			      void *private_data)
+			      void *private_data,
+			      int new_from_parent_fd)
 {
 	pid_t pid;
 	NTSTATUS status;
@@ -384,6 +371,7 @@ static void standard_new_task(struct tevent_context *ev,
 	if (state == NULL) {
 		return;
 	}
+	from_parent_fd = new_from_parent_fd;
 
 	pid = fork();
 
@@ -421,15 +409,11 @@ static void standard_new_task(struct tevent_context *ev,
 		smb_panic("Failed to re-initialise imessaging after fork");
 	}
 
-	fde = tevent_add_fd(ev, ev, child_pipe[0], TEVENT_FD_READ,
+	fde = tevent_add_fd(ev, ev, from_parent_fd, TEVENT_FD_READ,
 		      standard_pipe_handler, NULL);
 	if (fde == NULL) {
 		smb_panic("Failed to add fd handler after fork");
 	}
-	if (child_pipe[1] != -1) {
-		close(child_pipe[1]);
-		child_pipe[1] = -1;
-	}
 
 	se = tevent_add_signal(ev,
 				ev,
diff --git a/source4/smbd/server.c b/source4/smbd/server.c
index 249391c0dff..66f2794a38a 100644
--- a/source4/smbd/server.c
+++ b/source4/smbd/server.c
@@ -43,6 +43,11 @@
 #include "lib/util/samba_modules.h"
 #include "nsswitch/winbind_client.h"
 #include "libds/common/roles.h"
+#include "lib/util/tfork.h"
+
+#ifdef HAVE_PTHREAD
+#include <pthread.h>
+#endif
 
 struct server_state {
 	struct tevent_context *event_ctx;
@@ -332,6 +337,20 @@ static int event_ctx_destructor(struct tevent_context *event_ctx)
 	return 0;
 }
 
+#ifdef HAVE_PTHREAD
+static int to_children_fd = -1;
+static void atfork_prepare(void) {
+}
+static void atfork_parent(void) {
+}
+static void atfork_child(void) {
+	if (to_children_fd != -1) {
+		close(to_children_fd);
+		to_children_fd = -1;
+	}
+}
+#endif
+
 /*
  main server.
 */
@@ -608,12 +627,54 @@ static int binary_smbd_main(const char *binary_name,
 
 	DEBUG(0,("%s: using '%s' process model\n", binary_name, model));
 
-	status = server_service_startup(state->event_ctx, cmdline_lp_ctx, model,
-					lpcfg_server_services(cmdline_lp_ctx));
-	if (!NT_STATUS_IS_OK(status)) {
-		TALLOC_FREE(state);
-		exit_daemon("Samba failed to start services",
-			NT_STATUS_V(status));
+	{
+		int child_pipe[2];
+		int rc;
+		bool start_services = false;
+
+		rc = pipe(child_pipe);
+		if (rc < 0) {
+			TALLOC_FREE(state);
+			exit_daemon("Samba failed to open process control pipe",
+				    errno);
+		}
+		smb_set_close_on_exec(child_pipe[0]);
+		smb_set_close_on_exec(child_pipe[1]);
+
+#ifdef HAVE_PTHREAD
+		to_children_fd = child_pipe[1];
+		pthread_atfork(atfork_prepare, atfork_parent,
+			       atfork_child);
+		start_services = true;
+#else
+		pid_t pid;
+		struct tfork *t = NULL;
+		t = tfork_create();
+		if (t == NULL) {
+			exit_daemon(
+				"Samba unable to fork master process",
+				0);
+		}
+		pid = tfork_child_pid(t);
+		if (pid == 0) {
+			start_services = false;
+		} else {
+			/* In the child process */
+			start_services = true;
+			close(child_pipe[1]);
+		}
+#endif
+		if (start_services) {
+			status = server_service_startup(
+				state->event_ctx, cmdline_lp_ctx, model,
+				lpcfg_server_services(cmdline_lp_ctx),
+				child_pipe[0]);
+			if (!NT_STATUS_IS_OK(status)) {
+				TALLOC_FREE(state);
+				exit_daemon("Samba failed to start services",
+				NT_STATUS_V(status));
+			}
+		}
 	}
 
 	if (opt_daemon) {
diff --git a/source4/smbd/service.c b/source4/smbd/service.c
index 403ae74964b..61ed684d00f 100644
--- a/source4/smbd/service.c
+++ b/source4/smbd/service.c
@@ -56,13 +56,16 @@ NTSTATUS register_server_service(TALLOC_CTX *ctx,
 static NTSTATUS server_service_init(const char *name,
 				    struct tevent_context *event_context,
 				    struct loadparm_context *lp_ctx,
-				    const struct model_ops *model_ops)
+				    const struct model_ops *model_ops,
+				    int from_parent_fd)
 {
 	struct registered_server *srv;
 	for (srv=registered_servers; srv; srv=srv->next) {
 		if (strcasecmp(name, srv->service_name) == 0) {
-			return task_server_startup(event_context, lp_ctx, srv->service_name,
-						   model_ops, srv->task_init);
+			return task_server_startup(event_context, lp_ctx,
+						   srv->service_name,
+						   model_ops, srv->task_init,
+						   from_parent_fd);
 		}
 	}
 	return NT_STATUS_INVALID_SYSTEM_SERVICE;
@@ -72,9 +75,10 @@ static NTSTATUS server_service_init(const char *name,
 /*
   startup all of our server services
 */
-NTSTATUS server_service_startup(struct tevent_context *event_ctx, 
+NTSTATUS server_service_startup(struct tevent_context *event_ctx,
 				struct loadparm_context *lp_ctx,
-				const char *model, const char **server_services)
+				const char *model, const char **server_services,
+				int from_parent_fd)
 {
 	int i;
 	const struct model_ops *model_ops;
@@ -93,7 +97,8 @@ NTSTATUS server_service_startup(struct tevent_context *event_ctx,
 	for (i=0;server_services[i];i++) {
 		NTSTATUS status;
 
-		status = server_service_init(server_services[i], event_ctx, lp_ctx, model_ops);
+		status = server_service_init(server_services[i], event_ctx,
+					     lp_ctx, model_ops, from_parent_fd);
 		if (!NT_STATUS_IS_OK(status)) {
 			DEBUG(0,("Failed to start service '%s' - %s\n", 
 				 server_services[i], nt_errstr(status)));
diff --git a/source4/smbd/service_task.c b/source4/smbd/service_task.c
index 34f73d9f4b2..e0e98f644e1 100644
--- a/source4/smbd/service_task.c
+++ b/source4/smbd/service_task.c
@@ -101,7 +101,8 @@ NTSTATUS task_server_startup(struct tevent_context *event_ctx,
 			     struct loadparm_context *lp_ctx,
 			     const char *service_name, 
 			     const struct model_ops *model_ops, 
-			     void (*task_init)(struct task_server *))
+			     void (*task_init)(struct task_server *),
+			     int from_parent_fd)
 {
 	struct task_state *state;
 
@@ -110,8 +111,10 @@ NTSTATUS task_server_startup(struct tevent_context *event_ctx,
 
 	state->task_init = task_init;
 	state->model_ops = model_ops;
-	
-	model_ops->new_task(event_ctx, lp_ctx, service_name, task_server_callback, state);
+
+	state->model_ops->new_task(event_ctx, lp_ctx, service_name,
+			           task_server_callback, state,
+				   from_parent_fd);
 
 	return NT_STATUS_OK;
 }