1 files changed, 74 insertions, 6 deletions

diff --git a/nldev-handler.c b/nldev-handler.c
index 4fa6e2a..f4f7eb4 100644
--- a/nldev-handler.c
+++ b/nldev-handler.c
@@ -1,12 +1,17 @@
 
+#include <errno.h>
 #include <fcntl.h>
 #include <poll.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
+
 #include <sys/types.h>
 #include <sys/wait.h>
+#include <sys/socket.h>
+
+#include <linux/netlink.h>
 
 #include "log.h"
 
@@ -33,21 +38,31 @@ child(char *runpath)
 void
 usage(void)
 {
-	die("usage: %s [-d] [-r run]\n", argv0);
+	die("usage: %s [-dku] [-f subsystem] [-r run]\n", argv0);
 }
 
 int main(int argc, char *argv[])
 {
 	struct pollfd fds;
 	int r;
-	static char buf[16384];
 	char *runpath = "/bin/mdev";
 	char *subsystem = NULL;
 
+	int showudev, showkernel;
+
+	showudev = 1;
+	showkernel = 1;
+
 	ARGBEGIN {
 	case 'd':
 		dodebug = 1;
 		break;
+	case 'k':
+		showudev = 0;
+		break;
+	case 'u':
+		showkernel = 0;
+		break;
 	case 'r':
 		runpath = EARGF(usage());
 		break;
@@ -66,6 +81,13 @@ int main(int argc, char *argv[])
 		size_t len;
 		int i, slen;
 		char *key, *value;
+		struct iovec iov;
+		char cbuf[CMSG_SPACE(sizeof(struct ucred))];
+		char buf[16384];
+		struct cmsghdr *chdr;
+		struct ucred *cred;
+		struct msghdr hdr;
+		struct sockaddr_nl cnls;
 
 		clearenv();
 		setenv("PATH", "/sbin:/bin", 1);
@@ -73,11 +95,57 @@ int main(int argc, char *argv[])
 		if (!(fds.revents & POLLIN))
 			continue;
 
-		len = read(fds.fd, buf, sizeof(buf)-1);
-		buf[len] = 0;
-		dbg("Got %u bytes", len);
+		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.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;
+		}
 
-		slen = 0;
 		for (i = 0; i < len; i += slen + 1) {
 			key = buf + i;
 			value = strchr(key, '=');