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From:   Mathias Nyman <mathias.nyman@linux.intel.com>
To:     Mayank Rana <quic_mrana@quicinc.com>, peter.chen@kernel.org,
        balbi@kernel.org, stern@rowland.harvard.edu,
        chunfeng.yun@mediatek.com, gregkh@linuxfoundation.org
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 <71347c81-3887-d80e-707b-c0f1018b1a50@linux.intel.com>
Subject: Re: [PATCH RESEND] xhci: Use xhci_get_virt_ep() to validate ep_index
Message-ID: <06d5e94f-1c3b-9ab1-b4ff-79007026585a@linux.intel.com>
Date:   Fri, 29 Apr 2022 13:13:01 +0300
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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