linux-kernel - Re: [PATCH RESEND] xhci: Use xhci_get_virt_ep() to validate ep

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Date:   Fri, 29 Apr 2022 12:01:56 -0700
From:   Mayank Rana <quic_mrana@...cinc.com>
To:     Mathias Nyman <mathias.nyman@...ux.intel.com>,
        <peter.chen@...nel.org>, <balbi@...nel.org>,
        <stern@...land.harvard.edu>, <chunfeng.yun@...iatek.com>,
        <gregkh@...uxfoundation.org>
CC:     <linux-kernel@...r.kernel.org>, <linux-usb@...r.kernel.org>
Subject: Re: [PATCH RESEND] xhci: Use xhci_get_virt_ep() to validate ep_index

On 4/29/2022 3:13 AM, Mathias Nyman wrote:
> On 29.4.2022 12.49, Mathias Nyman wrote:
>> On 28.4.2022 22.04, Mayank Rana wrote:
>>> ring_doorbell_for_active_rings() API is being called from
>>> multiple context. This specific API tries to get virt_dev
>>> based endpoint using passed slot_id and ep_index. Some caller
>>> API is having check against slot_id and ep_index using
>>> xhci_get_virt_ep() API whereas xhci_handle_cmd_config_ep() API
>>> only check ep_index against -1 value but not upper bound i.e.
>>> EP_CTX_PER_DEV. Hence use xhci_get_virt_ep() API to get virt_dev
>>> based endpoint which checks both slot_id and ep_index to get
>>> valid endpoint.
>> ep_index upper bound is known to be in range as EP_CTX_PER_DEV is 31,
>> and ep_index = fls(u32 value)  - 1 - 1;
>>
>> We can change to use xhci_get_virt_ep(), but this would be more useful
>> earlier in xhci_handle_cmd_config_ep() where we touch the ep before
>> calling ring_doorbell_for_active_rings()
>>
> After a second look I would appreciate if you could clean up
> ep_index checking in xhci_handle_cmd_config_ep()
>
> It currenty does some horrible typecasting.
> ep_index is an unsigned int, so the fls() -1 operation might wrap it around.
> Checking this was solved by typecasting a -1 to an unsigned int.
>
> if (ep_index != (unsigned int) -1)
>
> Thanks
> Mathias

Thanks Mathias for review and suggestion here.
let me try to clean up xhci_handle_cmd_config_ep() API based ep_index 
usage.