From 0de38b3f6324744b81b8bf837fea384938f88557 Mon Sep 17 00:00:00 2001
From: hselasky <hselasky@ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f>
Date: Mon, 30 Jul 2018 09:22:21 +0000
Subject: [PATCH] MFC r335700: Improve the kernel's USB descriptor reading
 function. Some USB devices does not allow a partial descriptor readout.

Found by:	bz@
Sponsored by:	Mellanox Technologies


git-svn-id: svn://svn.freebsd.org/base/stable/9@336888 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f
---
 sys/dev/usb/usb_request.c | 29 +++++++++++++++++++++++++++--
 1 file changed, 27 insertions(+), 2 deletions(-)

diff --git a/sys/dev/usb/usb_request.c b/sys/dev/usb/usb_request.c
index 874a5ffff..f2c6e2db3 100644
--- a/sys/dev/usb/usb_request.c
+++ b/sys/dev/usb/usb_request.c
@@ -981,7 +981,7 @@ usbd_req_get_desc(struct usb_device *udev,
     uint8_t retries)
 {
 	struct usb_device_request req;
-	uint8_t *buf;
+	uint8_t *buf = desc;
 	usb_error_t err;
 
 	DPRINTFN(4, "id=%d, type=%d, index=%d, max_len=%d\n",
@@ -1003,6 +1003,32 @@ usbd_req_get_desc(struct usb_device *udev,
 		err = usbd_do_request_flags(udev, mtx, &req,
 		    desc, 0, NULL, 500 /* ms */);
 
+		if (err != 0 && err != USB_ERR_TIMEOUT &&
+		    min_len != max_len) {
+			/* clear descriptor data */
+			memset(desc, 0, max_len);
+
+			/* try to read full descriptor length */
+			USETW(req.wLength, max_len);
+
+			err = usbd_do_request_flags(udev, mtx, &req,
+			    desc, USB_SHORT_XFER_OK, NULL, 500 /* ms */);
+
+			if (err == 0) {
+				/* verify length */
+				if (buf[0] > max_len)
+					buf[0] = max_len;
+				else if (buf[0] < 2)
+					err = USB_ERR_INVAL;
+
+				min_len = buf[0];
+
+				/* enforce descriptor type */
+				buf[1] = type;
+				goto done;
+			}
+		}
+
 		if (err) {
 			if (!retries) {
 				goto done;
@@ -1013,7 +1039,6 @@ usbd_req_get_desc(struct usb_device *udev,
 
 			continue;
 		}
-		buf = desc;
 
 		if (min_len == max_len) {
 
-- 
2.42.0