libqb/backport-ipc_shm-Don-t-truncate-SHM-files-of-an-active-server.patch

From 75ab31bdd05a15947dc56edf4d6b7f377355435e Mon Sep 17 00:00:00 2001
From: Chrissie Caulfield <ccaulfie@redhat.com>
Date: Fri, 20 Apr 2018 09:48:04 +0100
Subject: [PATCH] ipc_shm: Don't truncate SHM files of an active server (#307)

* ipc_shm: Don't truncate SHM files of an active server

I've put in an extra check so that clients don't truncate the
SHM file if the server still exists. Sadly on FreeBSD we can't
get the server PID for the client (unless someone has a patch handy!)
so we still do the truncate when disconnected. As a backstop (and also
to cover the BSD issue) I've added a SIGBUS trap to the server shutdown
so that it doesn't cause a server crash.

Signed-off-by: Christine Caulfield <ccaulfie@redhat.com>
Reviewed by: Jan Friesse <jfriesse@redhat.com>
---
 include/qb/qbipcs.h |  4 ++++
 lib/ipc_int.h       |  1 +
 lib/ipc_setup.c     |  1 +
 lib/ipc_shm.c       | 48 +++++++++++++++++++++++++++++++++++----------
 tests/check_ipc.c   | 24 +++++++++++++++++------
 5 files changed, 62 insertions(+), 16 deletions(-)

diff --git a/include/qb/qbipcs.h b/include/qb/qbipcs.h
index 55c0f815..7b4daa7d 100644
--- a/include/qb/qbipcs.h
+++ b/include/qb/qbipcs.h
@@ -142,6 +142,10 @@ typedef void (*qb_ipcs_connection_created_fn) (qb_ipcs_connection_t *c);
  * successfully created.
  * @note if you return anything but 0 this function will be
  * repeatedly called (until 0 is returned).
+ *
+ * With SHM connections libqb will briefly trap SIGBUS during the
+ * disconnect process to guard against server crashes if the mapped
+ * file is truncated. The signal will be restored afterwards.
  */
 typedef int32_t (*qb_ipcs_connection_closed_fn) (qb_ipcs_connection_t *c);
 
diff --git a/lib/ipc_int.h b/lib/ipc_int.h
index 67fc444c..9cd06cfe 100644
--- a/lib/ipc_int.h
+++ b/lib/ipc_int.h
@@ -92,6 +92,7 @@ struct qb_ipcc_connection {
 	char name[NAME_MAX];
 	int32_t needs_sock_for_poll;
 	gid_t egid;
+	pid_t server_pid;
 	struct qb_ipc_one_way setup;
 	struct qb_ipc_one_way request;
 	struct qb_ipc_one_way response;
diff --git a/lib/ipc_setup.c b/lib/ipc_setup.c
index 57d755b4..0e169643 100644
--- a/lib/ipc_setup.c
+++ b/lib/ipc_setup.c
@@ -494,6 +494,7 @@ qb_ipcc_us_setup_connect(struct qb_ipcc_connection *c,
 
 	qb_ipc_auth_creds(data);
 	c->egid = data->ugp.gid;
+	c->server_pid = data->ugp.pid;
 
 	destroy_ipc_auth_data(data);
 	return r->hdr.error;
diff --git a/lib/ipc_shm.c b/lib/ipc_shm.c
index 699f4e47..9f237b6e 100644
--- a/lib/ipc_shm.c
+++ b/lib/ipc_shm.c
@@ -20,6 +20,8 @@
  */
 #include "os_base.h"
 #include <poll.h>
+#include <signal.h>
+#include <setjmp.h>
 
 #include "ipc_int.h"
 #include "util_int.h"
@@ -36,9 +38,12 @@
 static void
 qb_ipcc_shm_disconnect(struct qb_ipcc_connection *c)
 {
-	void (*rb_destructor)(struct qb_ringbuffer_s *) = c->is_connected
-		? qb_rb_close
-		: qb_rb_force_close;
+	void (*rb_destructor)(struct qb_ringbuffer_s *);
+
+	rb_destructor = qb_rb_close;
+	if (!c->is_connected && (!c->server_pid || (kill(c->server_pid, 0) == -1 && errno == ESRCH))) {
+		rb_destructor = qb_rb_force_close;
+	}
 
 	qb_ipcc_us_sock_close(c->setup.u.us.sock);
 
@@ -215,18 +220,30 @@ qb_ipcc_shm_connect(struct qb_ipcc_connection * c,
  * service functions
  * --------------------------------------------------------
  */
+static jmp_buf sigbus_jmpbuf;
+static void catch_sigbus(int signal)
+{
+	longjmp(sigbus_jmpbuf, 1);
+}
 
 static void
 qb_ipcs_shm_disconnect(struct qb_ipcs_connection *c)
 {
-	if (c->state == QB_IPCS_CONNECTION_ESTABLISHED ||
-	    c->state == QB_IPCS_CONNECTION_ACTIVE) {
-		if (c->setup.u.us.sock > 0) {
-			(void)c->service->poll_fns.dispatch_del(c->setup.u.us.sock);
-			qb_ipcc_us_sock_close(c->setup.u.us.sock);
-			c->setup.u.us.sock = -1;
-		}
+	struct sigaction sa;
+	struct sigaction old_sa;
+
+	/* Don't die if the client has truncated the SHM under us */
+	memset(&old_sa, 0, sizeof(old_sa));
+	memset(&sa, 0, sizeof(sa));
+	sa.sa_handler = catch_sigbus;
+	sigemptyset(&sa.sa_mask);
+	sa.sa_flags = 0;
+	sigaction(SIGBUS, &sa, &old_sa);
+
+	if (setjmp(sigbus_jmpbuf) == 1) {
+		goto end_disconnect;
 	}
+
 	if (c->state == QB_IPCS_CONNECTION_SHUTTING_DOWN ||
 	    c->state == QB_IPCS_CONNECTION_ACTIVE) {
 		if (c->response.u.shm.rb) {
@@ -239,6 +256,17 @@ qb_ipcs_shm_disconnect(struct qb_ipcs_connection *c)
 			qb_rb_close(qb_rb_lastref_and_ret(&c->request.u.shm.rb));
 		}
 	}
+
+	if (c->state == QB_IPCS_CONNECTION_ESTABLISHED ||
+	    c->state == QB_IPCS_CONNECTION_ACTIVE) {
+		if (c->setup.u.us.sock > 0) {
+			(void)c->service->poll_fns.dispatch_del(c->setup.u.us.sock);
+			qb_ipcc_us_sock_close(c->setup.u.us.sock);
+			c->setup.u.us.sock = -1;
+		}
+	}
+end_disconnect:
+	sigaction(SIGBUS, &old_sa, NULL);
 }
 
 static int32_t
diff --git a/tests/check_ipc.c b/tests/check_ipc.c
index f8af2c5e..46c3b404 100644
--- a/tests/check_ipc.c
+++ b/tests/check_ipc.c
@@ -444,18 +444,30 @@ run_ipc_server(void)
 static pid_t
 run_function_in_new_process(void (*run_ipc_server_fn)(void))
 {
-	pid_t pid = fork ();
+	pid_t pid1 = fork ();
+	pid_t pid2;
 
-	if (pid == -1) {
+	if (pid1 == -1) {
 		fprintf (stderr, "Can't fork\n");
 		return -1;
 	}
 
-	if (pid == 0) {
-		run_ipc_server_fn();
-		exit(0);
+	/* Double-fork so the servers can be reaped in a timely manner */
+	if (pid1 == 0) {
+		pid2 = fork();
+		if (pid2 == -1) {
+			fprintf (stderr, "Can't fork twice\n");
+			exit(0);
+		}
+		if (pid2 == 0) {
+			run_ipc_server_fn();
+			exit(0);
+		} else {
+			waitpid(pid2, NULL, 0);
+			exit(0);
+		}
 	}
-	return pid;
+	return pid1;
 }
 
 static void