linux-kernel - [PATCH 3.10 038/250] usb: gadget: composite: Test get_alt() presence instead of set

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Message-Id: <1496876436-32402-39-git-send-email-w@1wt.eu>
Date:   Thu,  8 Jun 2017 00:57:04 +0200
From:   Willy Tarreau <w@....eu>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        linux@...ck-us.net
Cc:     Krzysztof Opasiak <k.opasiak@...sung.com>,
        Felipe Balbi <felipe.balbi@...ux.intel.com>,
        Willy Tarreau <w@....eu>
Subject: [PATCH 3.10 038/250] usb: gadget: composite: Test get_alt() presence instead of set_alt()

From: Krzysztof Opasiak <k.opasiak@...sung.com>

commit 7e4da3fcf7c9fe042f2f7cb7bf23861a899b4a8f upstream.

By convention (according to doc) if function does not provide
get_alt() callback composite framework should assume that it has only
altsetting 0 and should respond with error if host tries to set
other one.

After commit dd4dff8b035f ("USB: composite: Fix bug: should test
set_alt function pointer before use it")
we started checking set_alt() callback instead of get_alt().
This check is useless as we check if set_alt() is set inside
usb_add_function() and fail if it's NULL.

Let's fix this check and move comment about why we check the get
method instead of set a little bit closer to prevent future false
fixes.

Fixes: dd4dff8b035f ("USB: composite: Fix bug: should test set_alt function pointer before use it")
Signed-off-by: Krzysztof Opasiak <k.opasiak@...sung.com>
Signed-off-by: Felipe Balbi <felipe.balbi@...ux.intel.com>
Signed-off-by: Willy Tarreau <w@....eu>
---
 drivers/usb/gadget/composite.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/gadget/composite.c b/drivers/usb/gadget/composite.c
index a660716..584e43c 100644
--- a/drivers/usb/gadget/composite.c
+++ b/drivers/usb/gadget/composite.c
@@ -1320,9 +1320,7 @@ composite_setup(struct usb_gadget *gadget, const struct usb_ctrlrequest *ctrl)
 		value = min(w_length, (u16) 1);
 		break;
 
-	/* function drivers must handle get/set altsetting; if there's
-	 * no get() method, we know only altsetting zero works.
-	 */
+	/* function drivers must handle get/set altsetting */
 	case USB_REQ_SET_INTERFACE:
 		if (ctrl->bRequestType != USB_RECIP_INTERFACE)
 			goto unknown;
@@ -1331,7 +1329,13 @@ composite_setup(struct usb_gadget *gadget, const struct usb_ctrlrequest *ctrl)
 		f = cdev->config->interface[intf];
 		if (!f)
 			break;
-		if (w_value && !f->set_alt)
+
+		/*
+		 * If there's no get_alt() method, we know only altsetting zero
+		 * works. There is no need to check if set_alt() is not NULL
+		 * as we check this in usb_add_function().
+		 */
+		if (w_value && !f->get_alt)
 			break;
 		value = f->set_alt(f, w_index, w_value);
 		if (value == USB_GADGET_DELAYED_STATUS) {
-- 
2.8.0.rc2.1.gbe9624a