Re: [PATCH] udevd - client access authorization

[Kay Sievers <kay.sievers@vrfy.org>]

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On Wed, Feb 11, 2004 at 02:34:32PM -0800, Greg KH wrote:
> On Wed, Feb 11, 2004 at 04:04:04AM +0100, Kay Sievers wrote:
> > Here is the badly needed client authorization for udevd.
> > Since we switched to abstract namespace sockets, we are unable to
> > control the access of the socket by file permissions.
> > 
> > So here we send a ancillary credential message with every datagram,
> > to be able to verify the uid of the sender. The sender can't fake the
> > credentials, cause the kernel doesn't allow it for non root users.
> 
> Thanks a lot for fixing this up.  I wouldn't want any user to be able to
> add or remove devices from /dev by just talking through a socket.

Here is a small improvement. We check for the type of message we receive
and udevsend seems not to need all the credential setup stuff, the
kernel will fill it for us.

udevd now refuses to start as non root, cause it doesn't make any sense.

Are we changing the mode_t in udev.h to unsigned int now?

thanks,
Kay

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diff -Nru a/udevd.c b/udevd.c
--- a/udevd.c	Thu Feb 12 00:58:08 2004
+++ b/udevd.c	Thu Feb 12 00:58:08 2004
@@ -252,16 +252,19 @@
 	cmsg = CMSG_FIRSTHDR(&smsg);
 	cred = (struct ucred *) CMSG_DATA(cmsg);
 
+	if (cmsg == NULL || cmsg->cmsg_type != SCM_CREDENTIALS) {
+		dbg("no sender credentials received, message ignored");
+		goto skip;
+	}
+
 	if (cred->uid != 0) {
 		dbg("sender uid=%i, message ignored", cred->uid);
-		free(msg);
-		return;
+		goto skip;
 	}
 
 	if (strncmp(msg->magic, UDEV_MAGIC, sizeof(UDEV_MAGIC)) != 0 ) {
 		dbg("message magic '%s' doesn't match, ignore it", msg->magic);
-		free(msg);
-		return;
+		goto skip;
 	}
 
 	/* if no seqnum is given, we move straight to exec queue */
@@ -271,6 +274,11 @@
 	} else {
 		msg_queue_insert(msg);
 	}
+	return;
+
+skip:
+	free(msg);
+	return;
 }
 
 static void sig_handler(int signum)
@@ -316,6 +324,11 @@
 
 	init_logging("udevd");
 
+	if (getuid() != 0) {
+		dbg("need to be root, exit");
+		exit(1);
+	}
+
 	/* set signal handler */
 	act.sa_handler = sig_handler;
 	sigemptyset (&act.sa_mask);
@@ -336,14 +349,14 @@
 
 	ssock = socket(AF_LOCAL, SOCK_DGRAM, 0);
 	if (ssock == -1) {
-		dbg("error getting socket");
+		dbg("error getting socket, exit");
 		exit(1);
 	}
 
 	/* the bind takes care of ensuring only one copy running */
 	retval = bind(ssock, (struct sockaddr *) &saddr, addrlen);
 	if (retval < 0) {
-		dbg("bind failed\n");
+		dbg("bind failed, exit");
 		goto exit;
 	}
 
diff -Nru a/udevsend.c b/udevsend.c
--- a/udevsend.c	Thu Feb 12 00:58:08 2004
+++ b/udevsend.c	Thu Feb 12 00:58:08 2004
@@ -133,13 +133,6 @@
 	struct sockaddr_un saddr;
 	socklen_t addrlen;
 	int started_daemon = 0;
-	struct iovec iov;
-	struct msghdr smsg;
-	char cred_msg[CMSG_SPACE(sizeof(struct ucred))];
-	struct cmsghdr *cmsg;
-	struct ucred *cred;
-	
-
 
 #ifdef DEBUG
 	init_logging("udevsend");
@@ -183,32 +176,10 @@
 
 	size = build_hotplugmsg(&msg, action, devpath, subsystem, seq);
 
-	/* prepare message with credentials to authenticate ourself */
-	iov.iov_base = &msg;
-	iov.iov_len = size;
-
-	smsg.msg_name = &saddr;
-	smsg.msg_namelen = addrlen;
-	smsg.msg_iov = &iov;
-	smsg.msg_iovlen = 1;
-	smsg.msg_control = cred_msg;
-	smsg.msg_controllen = CMSG_LEN(sizeof(struct ucred));;
-	smsg.msg_flags = 0;
-
-	cmsg = CMSG_FIRSTHDR(&smsg);
-	cmsg->cmsg_level = SOL_SOCKET;
-	cmsg->cmsg_type = SCM_CREDENTIALS;
-	cmsg->cmsg_len = sizeof(cred_msg);
-	cred = (struct ucred *) CMSG_DATA(cmsg);
-	cred->uid = getuid();
-	cred->gid = getgid();
-	cred->pid = getpid();
-	cred->pid = getpid();
-
 	/* If we can't send, try to start daemon and resend message */
 	loop = UDEVSEND_CONNECT_RETRY;
 	while (loop--) {
-		retval = sendmsg(sock, &smsg, 0);
+		retval = sendto(sock, &msg, size, 0, (struct sockaddr *)&saddr, addrlen);
 		if (retval != -1) {
 			retval = 0;
 			goto close_and_exit;