[RFC PATCH] usb: gadget: composite: Fix NULL pointer dereference

[Kishon Vijay Abraham I <kishon@ti.com>]

commit f563d230903210acc ("usb: gadget: composite: add req_match method
to usb_function") accesses cdev->config even before set config
is invoked causing a NULL pointer dereferencing error while running
Lecroy Mass Storage Compliance test.

Fix it here by accessing cdev->config only if it is non NULL.

Fixes: commit f563d230903210acc ("usb: gadget: composite: add req_match
method to usb_function").

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
---
Running Mass Storage Examples (TD.1.01 Interface Descriptor Test) in Lecroy
Compliance Suite produces this NULL pointer dereference abort.

The request is actually
"non-core control reqa0.06 v2a00 i0000 l12"

Tested this patch using USB3 Gen X CV (ch9 tests: usb2 and usb3,
link layer testing and MSC tests) and using USB2 X CV (ch9 tests,
MSC tests) and verified this doesn't cause any failures.

 drivers/usb/gadget/composite.c |   11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/gadget/composite.c b/drivers/usb/gadget/composite.c
index 4e3447b..58b4657 100644
--- a/drivers/usb/gadget/composite.c
+++ b/drivers/usb/gadget/composite.c
@@ -1758,10 +1758,13 @@ unknown:
 		 * take such requests too, if that's ever needed:  to work
 		 * in config 0, etc.
 		 */
-		list_for_each_entry(f, &cdev->config->functions, list)
-			if (f->req_match && f->req_match(f, ctrl))
-				goto try_fun_setup;
-		f = NULL;
+		if (cdev->config) {
+			list_for_each_entry(f, &cdev->config->functions, list)
+				if (f->req_match && f->req_match(f, ctrl))
+					goto try_fun_setup;
+			f = NULL;
+		}
+
 		switch (ctrl->bRequestType & USB_RECIP_MASK) {
 		case USB_RECIP_INTERFACE:
 			if (!cdev->config || intf >= MAX_CONFIG_INTERFACES)
-- 
1.7.9.5