linux-kernel - [PATCH] usb: gadget: net2272: assert for a valid dma request

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Message-Id: <20200830183646.24930-1-trix@redhat.com>
Date:   Sun, 30 Aug 2020 11:36:46 -0700
From:   trix@...hat.com
To:     balbi@...nel.org, gregkh@...uxfoundation.org,
        natechancellor@...il.com, ndesaulniers@...gle.com,
        christophe.jaillet@...adoo.fr, peter.chen@....com, b-liu@...com,
        chunfeng.yun@...iatek.com, novikov@...ras.ru, yanaijie@...wei.com
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Tom Rix <trix@...hat.com>
Subject: [PATCH] usb: gadget: net2272: assert for a valid dma request

From: Tom Rix <trix@...hat.com>

clang static analysis flags this representive problem

net2272.c:1541:8: warning: Dereference of null pointer
    if ((req->req.length % ep->ep.maxpacket != 0) ||
         ^~~~~~~~~~~~~~~
This is mostly not a problem.

In net2272_handle_dma(), even though every path through
the routine dereferences req, it is set to NULL when the
ep->queue is empty.  If the eq->queue was ever empty this
would have oops.

So the else statement should not be needed.  If it is,
flag it as a BUG.

Signed-off-by: Tom Rix <trix@...hat.com>
---
 drivers/usb/gadget/udc/net2272.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/gadget/udc/net2272.c b/drivers/usb/gadget/udc/net2272.c
index 44d1ea2307bb..8301723a8b1a 100644
--- a/drivers/usb/gadget/udc/net2272.c
+++ b/drivers/usb/gadget/udc/net2272.c
@@ -1506,17 +1506,16 @@ static int net2272_stop(struct usb_gadget *_gadget)
 static void
 net2272_handle_dma(struct net2272_ep *ep)
 {
-	struct net2272_request *req;
+	struct net2272_request *req = NULL;
 	unsigned len;
 	int status;
 
 	if (!list_empty(&ep->queue))
 		req = list_entry(ep->queue.next,
 				struct net2272_request, queue);
-	else
-		req = NULL;
 
 	dev_vdbg(ep->dev->dev, "handle_dma %s req %p\n", ep->ep.name, req);
+	BUG_ON(!req);
 
 	/* Ensure DREQ is de-asserted */
 	net2272_write(ep->dev, DMAREQ,
-- 
2.18.1