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SubjectRe: [PATCH] usb: gadget: net2272: assert for a valid dma request
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On 8/30/20 2:22 PM, Alan Stern wrote:
> On Sun, Aug 30, 2020 at 11:36:46AM -0700, trix@redhat.com wrote:
>> From: Tom Rix <trix@redhat.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@redhat.com>
> This patch really seems to be overkill. In particular, Linus Torvalds
> feels very strongly that people should not add BUG or BUG_ON calls
> except in extreme situations -- which this isn't.
>
>> ---
>> 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);
> There's no point in adding this. If the function goes on to dereference
> a NULL pointer, you'll get the same effect in any case -- an oops.
>
> If you want to make the point that req had better not be NULL, just get
> rid of the "if" test entirely. You could even change the list_entry to
> list_first_entry.

Since nothing is really going to change, drop this patch.

Tom

> Alan Stern
>

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