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

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Message-ID: <8e186a1d-23f9-dec8-234e-9599b65a65c2@linux.intel.com>
Date:   Fri, 6 May 2022 16:58:40 +0300
From:   Mathias Nyman <mathias.nyman@...ux.intel.com>
To:     Mayank Rana <quic_mrana@...cinc.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 29.4.2022 22.01, Mayank Rana wrote:
> 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.
> 

Please don't spend too much time on this,
I'm going to remove this code as Greg suggested.

Should have replied earlier, sorry about the delay

Thanks
-Mathias