linux-kernel - [PATCH 19/26] usb: gadget: udc: max3420_udc: remove using list iterator after loop body as a ptr

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Date:   Sun,  6 Mar 2022 18:50:27 +0100
From:   Jakob Koschel <jakobkoschel@...il.com>
To:     Greg Kroah-Hartman <greg@...ah.com>
Cc:     Jakob Koschel <jakobkoschel@...il.com>,
        linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Felipe Balbi <balbi@...nel.org>, Joel Stanley <joel@....id.au>,
        Andrew Jeffery <andrew@...id.au>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Claudiu Beznea <claudiu.beznea@...rochip.com>,
        Cristian Birsan <cristian.birsan@...rochip.com>,
        Al Cooper <alcooperx@...il.com>, Li Yang <leoyang.li@....com>,
        Vladimir Zapolskiy <vz@...ia.com>,
        Daniel Mack <daniel@...que.org>,
        Haojian Zhuang <haojian.zhuang@...il.com>,
        Robert Jarzmik <robert.jarzmik@...e.fr>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Michal Simek <michal.simek@...inx.com>,
        linux-usb@...r.kernel.org (open list:USB GADGET/PERIPHERAL SUBSYSTEM),
        Mike Rapoport <rppt@...nel.org>,
        "Brian Johannesmeyer" <bjohannesmeyer@...il.com>,
        Cristiano Giuffrida <c.giuffrida@...nl>,
        "Bos, H.J." <h.j.bos@...nl>
Subject: [PATCH 19/26] usb: gadget: udc: max3420_udc: remove using list iterator after loop body as a ptr

If the list does not contain the expected element, the value of
list_for_each_entry() iterator will not point to a valid structure.
To avoid type confusion in such case, the list iterator
scope will be limited to list_for_each_entry() loop.

In preparation to limiting scope of a list iterator to the list traversal
loop, use a dedicated pointer to point to the found element [1].
Determining if an element was found is then simply checking if
the pointer is != NULL instead of using the potentially bogus pointer.

Link: https://lore.kernel.org/all/YhdfEIwI4EdtHdym@kroah.com/
Signed-off-by: Jakob Koschel <jakobkoschel@...il.com>
---
 drivers/usb/gadget/udc/max3420_udc.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/drivers/usb/gadget/udc/max3420_udc.c b/drivers/usb/gadget/udc/max3420_udc.c
index d2a2b20cc1ad..d1b010b5f4a0 100644
--- a/drivers/usb/gadget/udc/max3420_udc.c
+++ b/drivers/usb/gadget/udc/max3420_udc.c
@@ -1044,22 +1044,25 @@ static int max3420_ep_queue(struct usb_ep *_ep, struct usb_request *_req,
 
 static int max3420_ep_dequeue(struct usb_ep *_ep, struct usb_request *_req)
 {
-	struct max3420_req *t, *req = to_max3420_req(_req);
+	struct max3420_req *t = NULL;
+	struct max3420_req *req = to_max3420_req(_req);
+	struct max3420_req *tmp;
 	struct max3420_ep *ep = to_max3420_ep(_ep);
 	unsigned long flags;
 
 	spin_lock_irqsave(&ep->lock, flags);
 
 	/* Pluck the descriptor from queue */
-	list_for_each_entry(t, &ep->queue, queue)
-		if (t == req) {
+	list_for_each_entry(tmp, &ep->queue, queue)
+		if (tmp == req) {
 			list_del_init(&req->queue);
+			t = tmp;
 			break;
 		}
 
 	spin_unlock_irqrestore(&ep->lock, flags);
 
-	if (t == req)
+	if (t)
 		max3420_req_done(req, -ECONNRESET);
 
 	return 0;
-- 
2.25.1