RDMA/ucma: Check that device exists prior to accessing it

Ensure that device exists prior to accessing its properties.

Reported-by: <syzbot+71655d44855ac3e76366@syzkaller.appspotmail.com>
Fixes: 75216638572f ("RDMA/cma: Export rdma cm interface to userspace")
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/core/ucma.c

@@ -1336,7 +1336,7 @@ static ssize_t ucma_notify(struct ucma_file *file, const char __user *inbuf,
 {
 	struct rdma_ucm_notify cmd;
 	struct ucma_context *ctx;
-	int ret;
+	int ret = -EINVAL;
 
 	if (copy_from_user(&cmd, inbuf, sizeof(cmd)))
 		return -EFAULT;
@@ -1345,7 +1345,9 @@ static ssize_t ucma_notify(struct ucma_file *file, const char __user *inbuf,
 	if (IS_ERR(ctx))
 		return PTR_ERR(ctx);
 
-	ret = rdma_notify(ctx->cm_id, (enum ib_event_type) cmd.event);
+	if (ctx->cm_id->device)
+		ret = rdma_notify(ctx->cm_id, (enum ib_event_type)cmd.event);
+
 	ucma_put_ctx(ctx);
 	return ret;
 }