nldev

commit e2d4a797b6364fd79fc6102d866f074409604815
parent e2c236b300e4fa9f4f7fdb672251892c2be3e149
Author: Christoph Lohmann <20h@r-36.net>
Date:   Sat, 28 Apr 2012 10:59:36 +0200

Adding security and nasty comments.

Diffstat:
config.mk
 | 
2
+-
nldev.1
 | 
4
++--
nldev.c
 | 
67
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--------

3 files changed, 62 insertions(+), 11 deletions(-)
diff --git a/config.mk b/config.mk
@@ -13,7 +13,7 @@ INCS = -I. -I/usr/include
 LIBS = -L/usr/lib -lc
 
 # flags
-CPPFLAGS = -DVERSION=\"${VERSION}\" -D_BSD_SOURCE
+CPPFLAGS = -DVERSION=\"${VERSION}\" -D_BSD_SOURCE -D_GNU_SOURCE
 CFLAGS = -g -std=c99 -pedantic -Wall -O0 ${INCS} ${CPPFLAGS}
 LDFLAGS = -static -g ${LIBS}
 #LDFLAGS = -s ${LIBS}
diff --git a/nldev.1 b/nldev.1
@@ -13,7 +13,7 @@
 .Op Fl d
 .Op Fl b 
 .Op Fl k
-.Op Fl l
+.Op Fl u
 .Op Fl f Ar subsystem
 .Op Fl r Ar runpath 
 .Ek
@@ -51,7 +51,7 @@ Show usage.
 Only show netlink messages from the kernel.
 .
 .Bd -filled
-.It Fl l
+.It Fl u
 Only show netlink messages from libudev.
 .
 .It Fl r Ar runpath
diff --git a/nldev.c b/nldev.c
@@ -92,7 +92,7 @@ child(char *runpath)
 	int fd, pid;
 
 	if (!(pid = fork())) {
-		if (dofork) {
+		if (dofork && !dodebug) {
 			fd = open("/dev/null", O_RDWR);
 			if (fd >= 0) {
 				if (write(0, 0, 0) < 0)
@@ -153,15 +153,20 @@ initsignals(void)
 void
 usage(void)
 {
-	die("usage: %s [-hdb] [-kl] [-f subsystem] [-r run]\n", argv0);
+	die("usage: %s [-hdb] [-ku] [-f subsystem] [-r run]\n", argv0);
 }
 
 int
 main(int argc, char *argv[])
 {
-	struct sockaddr_nl nls;
+	struct sockaddr_nl nls, cnls;
 	struct pollfd fds;
-	char buf[4097], *subsystem, *runpath, *key, *value;
+	struct msghdr hdr;
+	struct iovec iov;
+	char buf[4097], *subsystem, *runpath, *key, *value,
+	     cbuf[CMSG_SPACE(sizeof(struct ucred))];
+	struct cmsghdr *chdr;
+	struct ucred *cred;
 	int i, len, slen, showudev, showkernel;
 
 	showkernel = 1;
@@ -182,7 +187,7 @@ main(int argc, char *argv[])
 	case 'k':
 		showudev = 0;
 		break;
-	case 'l':
+	case 'u':
 		showkernel = 0;
 		break;
 	case 'r':
@@ -208,6 +213,11 @@ main(int argc, char *argv[])
 				sizeof(slen)) < 0) {
 		edie("setsockopt");
 	}
+	slen = 1;
+	if (setsockopt(fds.fd, SOL_SOCKET, SO_PASSCRED, &slen,
+				sizeof(slen)) < 0) {
+		edie("setsockopt");
+	}
 
 	if (bind(fds.fd, (void *)&nls, sizeof(nls)))
 		edie("bind");
@@ -234,16 +244,57 @@ main(int argc, char *argv[])
 		unsetenv("MINOR");
 		unsetenv("FIRMWARE");
 
-		len = recv(fds.fd, buf, sizeof(buf)-1, MSG_DONTWAIT);
-		if (len < 0)
+		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);
+
+		printf("recvmsg\n");
+		len = recvmsg(fds.fd, &hdr, 0);
+		if (len < 0 && errno == EINTR)
+			continue;
+		printf("check 2\n");
+		if (len < 32 || len >= sizeof(buf))
 			edie("recv");
 
-		if (strstr(buf, "libudev")) {
+		printf("chdr\n");
+		chdr = CMSG_FIRSTHDR(&hdr);
+		if (chdr == NULL || chdr->cmsg_type != SCM_CREDENTIALS)
+			continue;
+		printf("cred\n");
+
+		/*
+		 * 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;
+
+		printf("libudev\n");
+		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.pid > 0)
+				continue;
 		}
 
 		for (i = 0; i < len; i += slen + 1) {