[PATCH] udevd - client access authorization

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.

udevd is still working with klibc here :)

2 files changed, 61 insertions, 6 deletions

diff --git a/udevd.c b/udevd.c
index 104cb2b98..366c227a3 100644
--- a/udevd.c
+++ b/udevd.c
@@ -222,6 +222,11 @@ static void handle_msg(int sock)
 {
 	struct hotplug_msg *msg;
 	int retval;
+	struct msghdr smsg;
+	struct cmsghdr *cmsg;
+	struct iovec iov;
+	struct ucred *cred;
+	char cred_msg[CMSG_SPACE(sizeof(struct ucred))];
 
 	msg = msg_create();
 	if (msg == NULL) {
@@ -229,13 +234,30 @@ static void handle_msg(int sock)
 		return;
 	}
 
-	retval = recv(sock, msg, sizeof(struct hotplug_msg), 0);
+	iov.iov_base = msg;
+	iov.iov_len = sizeof(struct hotplug_msg);
+
+	memset(&smsg, 0x00, sizeof(struct msghdr));
+	smsg.msg_iov = &iov;
+	smsg.msg_iovlen = 1;
+	smsg.msg_control = cred_msg;
+	smsg.msg_controllen = sizeof(cred_msg);
+
+	retval = recvmsg(sock, &smsg, 0);
 	if (retval <  0) {
 		if (errno != EINTR)
 			dbg("unable to receive message");
 		return;
 	}
-	
+	cmsg = CMSG_FIRSTHDR(&smsg);
+	cred = (struct ucred *) CMSG_DATA(cmsg);
+
+	if (cred->uid != 0) {
+		dbg("sender uid=%i, message ignored", cred->uid);
+		free(msg);
+		return;
+	}
+
 	if (strncmp(msg->magic, UDEV_MAGIC, sizeof(UDEV_MAGIC)) != 0 ) {
 		dbg("message magic '%s' doesn't match, ignore it", msg->magic);
 		free(msg);
@@ -289,6 +311,7 @@ int main(int argc, char *argv[])
 	struct sockaddr_un saddr;
 	socklen_t addrlen;
 	int retval;
+	const int on = 1;
 	struct sigaction act;
 
 	init_logging("udevd");
@@ -324,6 +347,9 @@ int main(int argc, char *argv[])
 		goto exit;
 	}
 
+	/* enable receiving of the sender credentials */
+	setsockopt(ssock, SOL_SOCKET, SO_PASSCRED, &on, sizeof(on));
+
 	while (1) {
 		handle_msg(ssock);
 
diff --git a/udevsend.c b/udevsend.c
index a24e7d75e..b26c74442 100644
--- a/udevsend.c
+++ b/udevsend.c
@@ -119,7 +119,7 @@ static int start_daemon(void)
 
 int main(int argc, char* argv[])
 {
-	struct hotplug_msg message;
+	struct hotplug_msg msg;
 	char *action;
 	char *devpath;
 	char *subsystem;
@@ -133,6 +133,13 @@ int main(int argc, char* argv[])
 	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");
@@ -174,12 +181,34 @@ int main(int argc, char* argv[])
 	strcpy(&saddr.sun_path[1], UDEVD_SOCK_PATH);
 	addrlen = offsetof(struct sockaddr_un, sun_path) + strlen(saddr.sun_path+1) + 1;
 
-	size = build_hotplugmsg(&message, action, devpath, subsystem, seq);
-	
+	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 = sendto(sock, &message, size, 0, (struct sockaddr *)&saddr, addrlen);
+		retval = sendmsg(sock, &smsg, 0);
 		if (retval != -1) {
 			retval = 0;
 			goto close_and_exit;