[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 :)

1 files changed, 28 insertions, 2 deletions

diff --git a/udevd.c b/udevd.c
index 104cb2b987..366c227a3b 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);