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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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References: <1651172688-21439-1-git-send-email-quic_mrana@quicinc.com>
From:   Mathias Nyman <mathias.nyman@linux.intel.com>
Subject: Re: [PATCH RESEND] xhci: Use xhci_get_virt_ep() to validate ep_index
Message-ID: <71347c81-3887-d80e-707b-c0f1018b1a50@linux.intel.com>
Date:   Fri, 29 Apr 2022 12:49:59 +0300
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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()

Also note that this codepath is only used for some prototype
xHC controller that probably never made it to the market about 10 years ago. 

Thanks
Mathias