Code: int rds_recvmsg(struct kiocb *iocb, struct socket *sock, struct msghdr *msg,
		size_t size, int msg_flags)
{
	struct sock *sk = sock->sk;
	struct rds_sock *rs = rds_sk_to_rs(sk);
	long timeo;
	int ret = 0, nonblock = msg_flags & MSG_DONTWAIT;
	struct sockaddr_in *sin;
	struct rds_incoming *inc = NULL;

	/* udp_recvmsg()->sock_recvtimeo() gets away without locking too.. */
	timeo = sock_rcvtimeo(sk, nonblock);
 
 	rdsdebug("size %zu flags 0x%x timeo %ld\n", size, msg_flags, timeo);
 
 	if (msg_flags & MSG_OOB)
 		goto out;
 
	while (1) {
		/* If there are pending notifications, do those - and nothing else */
		if (!list_empty(&rs->rs_notify_queue)) {
			ret = rds_notify_queue_get(rs, msg);
			break;
		}

		if (rs->rs_cong_notify) {
			ret = rds_notify_cong(rs, msg);
			break;
		}

		if (!rds_next_incoming(rs, &inc)) {
			if (nonblock) {
				ret = -EAGAIN;
				break;
			}

			timeo = wait_event_interruptible_timeout(*sk_sleep(sk),
					(!list_empty(&rs->rs_notify_queue) ||
					 rs->rs_cong_notify ||
					 rds_next_incoming(rs, &inc)), timeo);
			rdsdebug("recvmsg woke inc %p timeo %ld\n", inc,
				 timeo);
			if (timeo > 0 || timeo == MAX_SCHEDULE_TIMEOUT)
				continue;

			ret = timeo;
			if (ret == 0)
				ret = -ETIMEDOUT;
			break;
		}

		rdsdebug("copying inc %p from %pI4:%u to user\n", inc,
			 &inc->i_conn->c_faddr,
			 ntohs(inc->i_hdr.h_sport));
		ret = inc->i_conn->c_trans->inc_copy_to_user(inc, msg->msg_iov,
							     size);
		if (ret < 0)
			break;

		/*
		 * if the message we just copied isn't at the head of the
		 * recv queue then someone else raced us to return it, try
		 * to get the next message.
		 */
		if (!rds_still_queued(rs, inc, !(msg_flags & MSG_PEEK))) {
			rds_inc_put(inc);
			inc = NULL;
			rds_stats_inc(s_recv_deliver_raced);
			continue;
		}

		if (ret < be32_to_cpu(inc->i_hdr.h_len)) {
			if (msg_flags & MSG_TRUNC)
				ret = be32_to_cpu(inc->i_hdr.h_len);
			msg->msg_flags |= MSG_TRUNC;
		}

		if (rds_cmsg_recv(inc, msg)) {
			ret = -EFAULT;
			goto out;
		}

		rds_stats_inc(s_recv_delivered);

		sin = (struct sockaddr_in *)msg->msg_name;
		if (sin) {
			sin->sin_family = AF_INET;
 			sin->sin_port = inc->i_hdr.h_sport;
 			sin->sin_addr.s_addr = inc->i_saddr;
 			memset(sin->sin_zero, 0, sizeof(sin->sin_zero));
 		}
 		break;
 	}

	if (inc)
		rds_inc_put(inc);

out:
	return ret;
}

Vulnerability Type: +Info 
CWE ID: CWE-200
Summary: The rds_recvmsg function in net/rds/recv.c in the Linux kernel before 3.0.44 does not initialize a certain structure member, which allows local users to obtain potentially sensitive information from kernel stack memory via a (1) recvfrom or (2) recvmsg system call on an RDS socket.
Commit Message: rds: set correct msg_namelen

Jay Fenlason (fenlason@redhat.com) found a bug,
that recvfrom() on an RDS socket can return the contents of random kernel
memory to userspace if it was called with a address length larger than
sizeof(struct sockaddr_in).
rds_recvmsg() also fails to set the addr_len paramater properly before
returning, but that's just a bug.
There are also a number of cases wher recvfrom() can return an entirely bogus
address. Anything in rds_recvmsg() that returns a non-negative value but does
not go through the "sin = (struct sockaddr_in *)msg->msg_name;" code path
at the end of the while(1) loop will return up to 128 bytes of kernel memory
to userspace.

And I write two test programs to reproduce this bug, you will see that in
rds_server, fromAddr will be overwritten and the following sock_fd will be
destroyed.
Yes, it is the programmer's fault to set msg_namelen incorrectly, but it is
better to make the kernel copy the real length of address to user space in
such case.

How to run the test programs ?
I test them on 32bit x86 system, 3.5.0-rc7.

1 compile
gcc -o rds_client rds_client.c
gcc -o rds_server rds_server.c

2 run ./rds_server on one console

3 run ./rds_client on another console

4 you will see something like:
server is waiting to receive data...
old socket fd=3
server received data from client:data from client
msg.msg_namelen=32
new socket fd=-1067277685
sendmsg()
: Bad file descriptor

/***************** rds_client.c ********************/

int main(void)
{
	int sock_fd;
	struct sockaddr_in serverAddr;
	struct sockaddr_in toAddr;
	char recvBuffer[128] = "data from client";
	struct msghdr msg;
	struct iovec iov;

	sock_fd = socket(AF_RDS, SOCK_SEQPACKET, 0);
	if (sock_fd < 0) {
		perror("create socket error\n");
		exit(1);
	}

	memset(&serverAddr, 0, sizeof(serverAddr));
	serverAddr.sin_family = AF_INET;
	serverAddr.sin_addr.s_addr = inet_addr("127.0.0.1");
	serverAddr.sin_port = htons(4001);

	if (bind(sock_fd, (struct sockaddr*)&serverAddr, sizeof(serverAddr)) < 0) {
		perror("bind() error\n");
		close(sock_fd);
		exit(1);
	}

	memset(&toAddr, 0, sizeof(toAddr));
	toAddr.sin_family = AF_INET;
	toAddr.sin_addr.s_addr = inet_addr("127.0.0.1");
	toAddr.sin_port = htons(4000);
	msg.msg_name = &toAddr;
	msg.msg_namelen = sizeof(toAddr);
	msg.msg_iov = &iov;
	msg.msg_iovlen = 1;
	msg.msg_iov->iov_base = recvBuffer;
	msg.msg_iov->iov_len = strlen(recvBuffer) + 1;
	msg.msg_control = 0;
	msg.msg_controllen = 0;
	msg.msg_flags = 0;

	if (sendmsg(sock_fd, &msg, 0) == -1) {
		perror("sendto() error\n");
		close(sock_fd);
		exit(1);
	}

	printf("client send data:%s\n", recvBuffer);

	memset(recvBuffer, '\0', 128);

	msg.msg_name = &toAddr;
	msg.msg_namelen = sizeof(toAddr);
	msg.msg_iov = &iov;
	msg.msg_iovlen = 1;
	msg.msg_iov->iov_base = recvBuffer;
	msg.msg_iov->iov_len = 128;
	msg.msg_control = 0;
	msg.msg_controllen = 0;
	msg.msg_flags = 0;
	if (recvmsg(sock_fd, &msg, 0) == -1) {
		perror("recvmsg() error\n");
		close(sock_fd);
		exit(1);
	}

	printf("receive data from server:%s\n", recvBuffer);

	close(sock_fd);

	return 0;
}

/***************** rds_server.c ********************/

int main(void)
{
	struct sockaddr_in fromAddr;
	int sock_fd;
	struct sockaddr_in serverAddr;
	unsigned int addrLen;
	char recvBuffer[128];
	struct msghdr msg;
	struct iovec iov;

	sock_fd = socket(AF_RDS, SOCK_SEQPACKET, 0);
	if(sock_fd < 0) {
		perror("create socket error\n");
		exit(0);
	}

	memset(&serverAddr, 0, sizeof(serverAddr));
	serverAddr.sin_family = AF_INET;
	serverAddr.sin_addr.s_addr = inet_addr("127.0.0.1");
	serverAddr.sin_port = htons(4000);
	if (bind(sock_fd, (struct sockaddr*)&serverAddr, sizeof(serverAddr)) < 0) {
		perror("bind error\n");
		close(sock_fd);
		exit(1);
	}

	printf("server is waiting to receive data...\n");
	msg.msg_name = &fromAddr;

	/*
	 * I add 16 to sizeof(fromAddr), ie 32,
	 * and pay attention to the definition of fromAddr,
	 * recvmsg() will overwrite sock_fd,
	 * since kernel will copy 32 bytes to userspace.
	 *
	 * If you just use sizeof(fromAddr), it works fine.
	 * */
	msg.msg_namelen = sizeof(fromAddr) + 16;
	/* msg.msg_namelen = sizeof(fromAddr); */
	msg.msg_iov = &iov;
	msg.msg_iovlen = 1;
	msg.msg_iov->iov_base = recvBuffer;
	msg.msg_iov->iov_len = 128;
	msg.msg_control = 0;
	msg.msg_controllen = 0;
	msg.msg_flags = 0;

	while (1) {
		printf("old socket fd=%d\n", sock_fd);
		if (recvmsg(sock_fd, &msg, 0) == -1) {
			perror("recvmsg() error\n");
			close(sock_fd);
			exit(1);
		}
		printf("server received data from client:%s\n", recvBuffer);
		printf("msg.msg_namelen=%d\n", msg.msg_namelen);
		printf("new socket fd=%d\n", sock_fd);
		strcat(recvBuffer, "--data from server");
		if (sendmsg(sock_fd, &msg, 0) == -1) {
			perror("sendmsg()\n");
			close(sock_fd);
			exit(1);
		}
	}

	close(sock_fd);
	return 0;
}

Signed-off-by: Weiping Pan <wpan@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>