RDMA/uverbs: Use an unambiguous errno for method not supported

[ Upstream commit 3624a8f0 ]

Returning EOPNOTSUPP is problematic because it can also be
returned by the method function, and we use it in quite a few
places in drivers these days.

Instead, dedicate EPROTONOSUPPORT to indicate that the ioctl framework
is enabled but the requested object and method are not supported by
the kernel. No other case will return this code, and it lets userspace
know to fall back to write().

grep says we do not use it today in drivers/infiniband subsystem.
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Reviewed-by: Matan Barak <matanb@mellanox.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/infiniband/core/uverbs_ioctl.c

@@ -245,16 +245,13 @@ static long ib_uverbs_cmd_verbs(struct ib_device *ib_dev,
 	uintptr_t data[UVERBS_OPTIMIZE_USING_STACK_SZ / sizeof(uintptr_t)];
 #endif
 
-	if (hdr->reserved)
-		return -EINVAL;
-
 	object_spec = uverbs_get_object(ib_dev, hdr->object_id);
 	if (!object_spec)
-		return -EOPNOTSUPP;
+		return -EPROTONOSUPPORT;
 
 	method_spec = uverbs_get_method(object_spec, hdr->method_id);
 	if (!method_spec)
-		return -EOPNOTSUPP;
+		return -EPROTONOSUPPORT;
 
 	if ((method_spec->flags & UVERBS_ACTION_FLAG_CREATE_ROOT) ^ !file->ucontext)
 		return -EINVAL;
@@ -310,6 +307,16 @@ static long ib_uverbs_cmd_verbs(struct ib_device *ib_dev,
 
 	err = uverbs_handle_method(buf, ctx->uattrs, hdr->num_attrs, ib_dev,
 				   file, method_spec, ctx->uverbs_attr_bundle);
+
+	/*
+	 * EPROTONOSUPPORT is ONLY to be returned if the ioctl framework can
+	 * not invoke the method because the request is not supported.  No
+	 * other cases should return this code.
+	*/
+	if (unlikely(err == -EPROTONOSUPPORT)) {
+		WARN_ON_ONCE(err == -EPROTONOSUPPORT);
+		err = -EINVAL;
+	}
 out:
 #ifdef UVERBS_OPTIMIZE_USING_STACK_SZ
 	if (ctx_size > UVERBS_OPTIMIZE_USING_STACK_SZ)
@@ -348,7 +355,7 @@ long ib_uverbs_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 		}
 
 		if (hdr.reserved) {
-			err = -EOPNOTSUPP;
+			err = -EPROTONOSUPPORT;
 			goto out;
 		}