Code: int rds_cmsg_atomic(struct rds_sock *rs, struct rds_message *rm,
		    struct cmsghdr *cmsg)
{
	struct page *page = NULL;
	struct rds_atomic_args *args;
	int ret = 0;

	if (cmsg->cmsg_len < CMSG_LEN(sizeof(struct rds_atomic_args))
	 || rm->atomic.op_active)
		return -EINVAL;

	args = CMSG_DATA(cmsg);

	/* Nonmasked & masked cmsg ops converted to masked hw ops */
	switch (cmsg->cmsg_type) {
	case RDS_CMSG_ATOMIC_FADD:
		rm->atomic.op_type = RDS_ATOMIC_TYPE_FADD;
		rm->atomic.op_m_fadd.add = args->fadd.add;
		rm->atomic.op_m_fadd.nocarry_mask = 0;
		break;
	case RDS_CMSG_MASKED_ATOMIC_FADD:
		rm->atomic.op_type = RDS_ATOMIC_TYPE_FADD;
		rm->atomic.op_m_fadd.add = args->m_fadd.add;
		rm->atomic.op_m_fadd.nocarry_mask = args->m_fadd.nocarry_mask;
		break;
	case RDS_CMSG_ATOMIC_CSWP:
		rm->atomic.op_type = RDS_ATOMIC_TYPE_CSWP;
		rm->atomic.op_m_cswp.compare = args->cswp.compare;
		rm->atomic.op_m_cswp.swap = args->cswp.swap;
		rm->atomic.op_m_cswp.compare_mask = ~0;
		rm->atomic.op_m_cswp.swap_mask = ~0;
		break;
	case RDS_CMSG_MASKED_ATOMIC_CSWP:
		rm->atomic.op_type = RDS_ATOMIC_TYPE_CSWP;
		rm->atomic.op_m_cswp.compare = args->m_cswp.compare;
		rm->atomic.op_m_cswp.swap = args->m_cswp.swap;
		rm->atomic.op_m_cswp.compare_mask = args->m_cswp.compare_mask;
		rm->atomic.op_m_cswp.swap_mask = args->m_cswp.swap_mask;
		break;
	default:
		BUG(); /* should never happen */
	}

	rm->atomic.op_notify = !!(args->flags & RDS_RDMA_NOTIFY_ME);
	rm->atomic.op_silent = !!(args->flags & RDS_RDMA_SILENT);
	rm->atomic.op_active = 1;
	rm->atomic.op_recverr = rs->rs_recverr;
	rm->atomic.op_sg = rds_message_alloc_sgs(rm, 1);
	if (!rm->atomic.op_sg) {
		ret = -ENOMEM;
		goto err;
	}

	/* verify 8 byte-aligned */
	if (args->local_addr & 0x7) {
		ret = -EFAULT;
		goto err;
	}

	ret = rds_pin_pages(args->local_addr, 1, &page, 1);
	if (ret != 1)
		goto err;
	ret = 0;

	sg_set_page(rm->atomic.op_sg, page, 8, offset_in_page(args->local_addr));

	if (rm->atomic.op_notify || rm->atomic.op_recverr) {
		/* We allocate an uninitialized notifier here, because
		 * we don't want to do that in the completion handler. We
		 * would have to use GFP_ATOMIC there, and don't want to deal
		 * with failed allocations.
		 */
		rm->atomic.op_notifier = kmalloc(sizeof(*rm->atomic.op_notifier), GFP_KERNEL);
		if (!rm->atomic.op_notifier) {
			ret = -ENOMEM;
			goto err;
		}

		rm->atomic.op_notifier->n_user_token = args->user_token;
		rm->atomic.op_notifier->n_status = RDS_RDMA_SUCCESS;
	}

	rm->atomic.op_rkey = rds_rdma_cookie_key(args->cookie);
	rm->atomic.op_remote_addr = args->remote_addr + rds_rdma_cookie_offset(args->cookie);

	return ret;
 err:
 	if (page)
 		put_page(page);
 	kfree(rm->atomic.op_notifier);
 
 	return ret;
}

Vulnerability Type: 
CWE ID: CWE-476
Summary: In the Linux kernel through 4.14.13, the rds_cmsg_atomic function in net/rds/rdma.c mishandles cases where page pinning fails or an invalid address is supplied, leading to an rds_atomic_free_op NULL pointer dereference.
Commit Message: RDS: null pointer dereference in rds_atomic_free_op

set rm->atomic.op_active to 0 when rds_pin_pages() fails
or the user supplied address is invalid,
this prevents a NULL pointer usage in rds_atomic_free_op()

Signed-off-by: Mohamed Ghannam <simo.ghannam@gmail.com>
Acked-by: Santosh Shilimkar <santosh.shilimkar@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>