Re: [PATCH] USB: gadget: Reject endpoints with 0 maxpacket value

[Felipe Balbi <balbi@kernel.org>]

[-- Attachment #1: Type: text/plain, Size: 2166 bytes --]


Hi,

Greg KH <gregkh@linuxfoundation.org> writes:
> On Mon, Oct 28, 2019 at 10:54:26AM -0400, Alan Stern wrote:
>> Endpoints with a maxpacket length of 0 are probably useless.  They
>> can't transfer any data, and it's not at all unlikely that a UDC will
>> crash or hang when trying to handle a non-zero-length usb_request for
>> such an endpoint.  Indeed, dummy-hcd gets a divide error when trying
>> to calculate the remainder of a transfer length by the maxpacket
>> value, as discovered by the syzbot fuzzer.
>> 
>> Currently the gadget core does not check for endpoints having a
>> maxpacket value of 0.  This patch adds a check to usb_ep_enable(),
>> preventing such endpoints from being used.
>> 
>> As far as I know, none of the gadget drivers in the kernel tries to
>> create an endpoint with maxpacket = 0, but until now there has been
>> nothing to prevent userspace programs under gadgetfs or configfs from
>> doing it.
>> 
>> Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
>> Reported-and-tested-by: syzbot+8ab8bf161038a8768553@syzkaller.appspotmail.com
>> CC: <stable@vger.kernel.org>
>> 
>> ---
>> 
>> 
>> [as1925]
>> 
>> 
>>  drivers/usb/gadget/udc/core.c |   11 +++++++++++
>>  1 file changed, 11 insertions(+)
>> 
>> Index: usb-devel/drivers/usb/gadget/udc/core.c
>> ===================================================================
>> --- usb-devel.orig/drivers/usb/gadget/udc/core.c
>> +++ usb-devel/drivers/usb/gadget/udc/core.c
>> @@ -98,6 +98,17 @@ int usb_ep_enable(struct usb_ep *ep)
>>  	if (ep->enabled)
>>  		goto out;
>>  
>> +	/* UDC drivers can't handle endpoints with maxpacket size 0 */
>> +	if (usb_endpoint_maxp(ep->desc) == 0) {
>> +		/*
>> +		 * We should log an error message here, but we can't call
>> +		 * dev_err() because there's no way to find the gadget
>> +		 * given only ep.
>> +		 */
>> +		ret = -EINVAL;
>> +		goto out;
>> +	}
>> +
>>  	ret = ep->ops->enable(ep, ep->desc);
>>  	if (ret)
>>  		goto out;
>> 
>
> Felipe, I can take this now in my tree if I can get an ack.

Definitely:

Acked-by: Felipe Balbi <balbi@kernel.org>

-- 
balbi

[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 832 bytes --]