From 311b810b9e2660231935c085429d94c5567b9522 Mon Sep 17 00:00:00 2001
From: Natanael Copa <ncopa@alpinelinux.org>
Date: Sun, 15 Mar 2015 15:30:01 +0100
Subject: pass over the netlink socket to handler instead of using a pipe

hand over the netlink socket directly to the handler and let handler
read from netlink instead of forwarding the message via pipe.

This simplifies the logic of the longtime running netlink daemon and
it simplifies the handling of partially read messages since all reading
happens is done by the handler.
---
 nldev.c | 133 +++++++---------------------------------------------------------
 1 file changed, 14 insertions(+), 119 deletions(-)

(limited to 'nldev.c')

diff --git a/nldev.c b/nldev.c
index a771931..bbc8eb2 100644
--- a/nldev.c
+++ b/nldev.c
@@ -24,44 +24,22 @@
 #include "arg.h"
 #include "log.h"
 
-int listfd = -1;
 int dofork = 0;
 
-struct handler {
-	int fd;
-	int argc;
-	char **argv;
-};
-
-void
-spawn_handler(struct handler *child)
+pid_t
+spawn_handler(int fd, char **argv)
 {
-	int pipefd[2];
-
-	if (pipe(pipefd) == -1)
-		edie("pipe");
-
 	pid_t pid = fork();
 
 	if (pid < 0)
 		edie("fork");
 
 	if (pid == 0) {
-		close(pipefd[1]);
-		dup2(pipefd[0], 0);
-		execv(child->argv[0], child->argv);
+		dup2(fd, 0);
+		execv(argv[0], argv);
 		edie("execl");
 	}
-	close(pipefd[0]);
-	child->fd = pipefd[1];
-}
-
-int
-write_to_handler(struct handler *child, const char *buf, size_t count)
-{
-	if (child->fd == -1)
-		spawn_handler(child);
-	return write(child->fd, buf, count);
+	return pid;
 }
 
 void
@@ -129,25 +107,13 @@ init_netlink_socket(void)
 void
 usage(void)
 {
-	die("usage: %s [-hdb] [-ku] [-- run [...]]\n", argv0);
+	die("usage: %s [-bd] -- runpath [...]\n", argv0);
 }
 
 int
 main(int argc, char *argv[])
 {
-	struct sockaddr_nl cnls;
-	struct pollfd fds[2];
-	struct msghdr hdr;
-	struct iovec iov;
-	char buf[4097], cbuf[CMSG_SPACE(sizeof(struct ucred))];
-	struct cmsghdr *chdr;
-	struct ucred *cred;
-	int len, showudev, showkernel;
-
-	struct handler child;
-
-	showkernel = 1;
-	showudev = 1;
+	struct pollfd fds;
 
 	ARGBEGIN {
 	case 'b':
@@ -156,27 +122,12 @@ main(int argc, char *argv[])
 	case 'd':
 		dodebug = 1;
 		break;
-	case 'k':
-		showudev = 0;
-		break;
-	case 'u':
-		showkernel = 0;
-		break;
 	default:
 		usage();
 	} ARGEND;
 
-	child.fd = -1;
-	child.argc = argc;
-	child.argv = argv;
-
-	fds[0].events = POLLIN;
-	fds[0].fd = init_netlink_socket();
-
-	fds[1].fd = child.fd;
-	fds[1].events = POLLERR;
-
-	listfd = fds[0].fd;
+	fds.events = POLLIN;
+	fds.fd = init_netlink_socket();
 
 	if (dofork) {
 		if (daemon(0, 0) < 0)
@@ -186,68 +137,12 @@ main(int argc, char *argv[])
 
 	initsignals();
 
-	while (poll(fds, 2, -1) > -1) {
-		if (fds[1].revents & POLLERR) {
-			dbg("handler exited");
-			close(child.fd);
-			fds[1].fd = child.fd = -1;
-		}
-
-		if (!(fds[0].revents & POLLIN))
-			continue;
-
-		iov.iov_base = &buf;
-		iov.iov_len = sizeof(buf);
-		memset(&hdr, 0, sizeof(hdr));
-		hdr.msg_iov = &iov;
-		hdr.msg_iovlen = 1;
-		hdr.msg_control = cbuf;
-		hdr.msg_controllen = sizeof(cbuf);
-		hdr.msg_name = &cnls;
-		hdr.msg_namelen = sizeof(cnls);
-
-		len = recvmsg(fds[0].fd, &hdr, 0);
-		if (len < 0) {
-			if (errno == EINTR)
-				continue;
-			edie("recvmsg");
-		}
-		if (len < 32 || len >= sizeof(buf))
-			continue;
-
-		chdr = CMSG_FIRSTHDR(&hdr);
-		if (chdr == NULL || chdr->cmsg_type != SCM_CREDENTIALS)
-			continue;
-
-		/*
-		 * Don't allow anyone but root to send us messages.
-		 *
-		 * We will allow users to send us messages, when
-		 * udev is enabled. Udev is just a toy you should
-		 * only use for testing.
-		 */
-		cred = (struct ucred *)CMSG_DATA(chdr);
-		if (cred->uid != 0 && !showudev)
-			continue;
-
-		if (!memcmp(buf, "libudev", 8)) {
-			/*
-			 * Receiving messages from udev is insecure.
-			 */
-			if (!showudev)
-				continue;
-		} else {
-			if (!showkernel)
-				continue;
-			/*
-			 * Kernel messages shouldn't come from the
-			 * userspace.
-			 */
-			if (cnls.nl_pid > 0)
-				continue;
+	while (poll(&fds, 1, -1) > -1) {
+		if (fds.revents & POLLIN) {
+			int status;
+			pid_t childpid = spawn_handler(fds.fd, argv);
+			waitpid(childpid, &status, 0);
 		}
-		write_to_handler(&child, buf, len);
-		fds[1].fd = child.fd;
 	}
 
 	return 0;
-- 
cgit v1.2.3