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From: Mathias Nyman <>
To: Johan Hovold <>
Cc:,,, "# v5 . 3" <>
Subject: Re: [RFT PATCH] xhci: Fix use-after-free regression in xhci clear hub TT implementation
Date: Mon, 14 Oct 2019 16:18:49 +0300
Message-ID: <> (raw)
In-Reply-To: <20191014101611.GN13531@localhost>

On 14.10.2019 13.16, Johan Hovold wrote:
> On Fri, Oct 11, 2019 at 03:58:42PM +0300, Mathias Nyman wrote:
>> commit ef513be0a905 ("usb: xhci: Add Clear_TT_Buffer") schedules work
>> to clear TT buffer, but causes a use-after-free regression at the same time
>> Make sure hub_tt_work finishes before endpoint is disabled, otherwise
>> the work will dereference already freed endpoint and device related
>> pointers.
>> This was triggered when usb core failed to read the configuration
>> descriptor of a FS/LS device during enumeration.
>> xhci driver queued clear_tt_work while usb core freed and reallocated
>> a new device for the next enumeration attempt.
>> EHCI driver implents ehci_endpoint_disable() that makes sure
>> clear_tt_work has finished before it returns, but xhci lacks this support.
>> usb core will call hcd->driver->endpoint_disable() callback before
>> disabling endpoints, so we want this in xhci as well.
>> The added xhci_endpoint_disable() is based on ehci_endpoint_disable()
> I used essentially the same reproducer as you did for debugging this
> after I first hit it with an actually stalled control endpoint, and this
> patch works also with my fault-injection hack.
> I've reviewed the code and it looks good to me except for one mostly
> theoretical issue. You need to check ep->hc_priv while holding the
> xhci->lock in xhci_clear_tt_buffer_complete() or you could end up having
> xhci_endpoint_disable() reschedule indefinitely while waiting for
> EP_CLEARING_TT to be cleared on a sufficiently weakly ordered
> system.

Good point, I'll change that

> Since cfbb8a84c2d2 ("xhci: Fix NULL pointer dereference in
> xhci_clear_tt_buffer_complete()") isn't needed anymore and is slightly
> misleading, I suggest amending the patch with the following:

I'll add those changes and your tags to the patch


      reply index

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-04 11:59 [PATCH 0/8] xhci fixes for usb-linus Mathias Nyman
2019-10-04 11:59 ` [PATCH 1/8] xhci: Fix false warning message about wrong bounce buffer write length Mathias Nyman
2019-10-04 11:59 ` [PATCH 2/8] xhci: Prevent device initiated U1/U2 link pm if exit latency is too long Mathias Nyman
2019-10-04 11:59 ` [PATCH 3/8] xhci: Check all endpoints for LPM timeout Mathias Nyman
2019-10-04 11:59 ` [PATCH 4/8] xhci: Fix USB 3.1 capability detection on early xHCI 1.1 spec based hosts Mathias Nyman
2019-10-04 11:59 ` [PATCH 5/8] usb: xhci: wait for CNR controller not ready bit in xhci resume Mathias Nyman
2019-10-04 11:59 ` [PATCH 6/8] xhci: Prevent deadlock when xhci adapter breaks during init Mathias Nyman
2019-10-04 11:59 ` [PATCH 7/8] xhci: Increase STS_SAVE timeout in xhci_suspend() Mathias Nyman
     [not found]   ` <>
2019-10-07 18:51     ` Kai-Heng Feng
2019-10-04 11:59 ` [PATCH 8/8] xhci: Fix NULL pointer dereference in xhci_clear_tt_buffer_complete() Mathias Nyman
2019-10-07 14:02   ` Johan Hovold
2019-10-08  8:15     ` Mathias Nyman
2019-10-11 12:47       ` Mathias Nyman
2019-10-11 12:58         ` [RFT PATCH] xhci: Fix use-after-free regression in xhci clear hub TT implementation Mathias Nyman
2019-10-14 10:16           ` Johan Hovold
2019-10-14 13:18             ` Mathias Nyman [this message]

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