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Date: Tue, 07 Jun 2016 04:39:22 +0000
From: Chung-Geol Kim <chunggeol.kim@...sung.com>
To: Alan Stern <stern@...land.harvard.edu>
Cc: gregkh@...uxfoundation.org
<gregkh@...uxfoundation.org>,
mathias.nyman@...ux.intel.com
<mathias.nyman@...ux.intel.com>,
stefan.koch10@...il.com
<stefan.koch10@...il.com>,
hkallweit1@...il.com <hkallweit1@...il.com>,
sergei.shtylyov@...entembedded.com
<sergei.shtylyov@...entembedded.com>,
dan.j.williams@...el.com
<dan.j.williams@...el.com>,
sarah.a.sharp@...ux.intel.com
<sarah.a.sharp@...ux.intel.com>,
chris.bainbridge@...il.com
<chris.bainbridge@...il.com>,
linux-usb@...r.kernel.org
<linux-usb@...r.kernel.org>,
linux-kernel@...r.kernel.org
<linux-kernel@...r.kernel.org>
Subject: RE: Re: Re: Re: [PATCH] usb: core: fix a double free in the usb driver
>On Fri, 3 Jun 2016, Chung-Geol Kim wrote:
>
>> Yes, you are right, The presentational errors in order to obtain an understanding of the process.
>> Therefore, I will be happy to explain again the diagrammatic representation as shown below.
>> If using usb 3.0 storage(OTG), you can see as below.
>>
>> ==============================================
>> At *Insert USB(3.0) Storage
>> sequence <1> --> <5>
>> ==============================================
>> VOLD
>> =================================|============
>> (uevent)
>> ______|___________
>> |<5> |
>> | SCSI |
>> |usb_get_hcd |
>> |shared_hcd(kref=3)|
>> |__________________|
>> ___________________ ________|_________
>> |<2> | |<4> |
>> |dwc3_otg_sm_work | |dwc3_otg_sm_work |
>> |usb_get_hcd | |usb_get_hcd |
>> |primary_hcd(kref=2)| |shared_hcd(kref=2)|
>> |___________________| |__________________|
>> _________|_________ ________|_________
>> |<1> | |<3> |
>> |New USB BUS #1 | |New USB BUS #2 |
>> |usb_create_hcd | |usb_create_hcd |
>> |primary_hcd(kref=1)| |shared_hcd(kref=1)|
>> | | | |
>> |bandXX_mutex(alloc)|<-(Link)-bandXX_mutex |
>> |___________________| |__________________|
>>
>
>When people present diagrams like this, the universal convention is to
>show earlier times at the top and later times at the bottom. That way
>the order in which you read the diagram is the same as the order in
>which the events are supposed to occur.
>
>Also, the convention is to put events next to each other if they happen
>at the same time. In your diagram, <1> and <3> are next to each other
>but they don't happen at the same time.
Thank you for your kind explanation. It has been modified as shown below.
=================================================
At *Insert USB(3.0) Storage
sequence <1> --> <5>
=================================================
___________________
|<1> |
|New USB BUS #1 |
|usb_create_hcd |
|primary_hcd(kref=1)|
| |
|bandXX_mutex(alloc)|<--
|___________________| |
_________|_________ |
|<2> | |
|dwc3_otg_sm_work | |
|usb_get_hcd | |
|primary_hcd(kref=2)| |
|___________________| |
| __________________
| |<3> |
| |New USB BUS #2 |
| |usb_create_hcd |
| |shared_hcd(kref=1)|
| | |
--(Link)-bandXX_mutex|
|__________________|
________|_________
|<4> |
|dwc3_otg_sm_work |
|usb_get_hcd |
|shared_hcd(kref=2)|
|__________________|
_______|__________
|<5> |
| SCSI |
|usb_get_hcd |
|shared_hcd(kref=3)|
|__________________|
|
(uevent)
-----------------------------------|------------
VOLD
=================================================
=================================================
At *remove USB(3.0) Storage
sequence <1> --> <5> ((Normal Case))
=================================================
VOLD
------------------------------------|------------
(uevent)
______|___________
|<1> |
| SCSI |
|usb_put_hcd |
|shared_hcd(kref=2)|
|__________________|
________|_________
|<2> |
|dwc3_otg_sm_work |
|usb_put_hcd |
|shared_hcd(kref=1)|
|__________________|
________|_________
|<3> |
|New USB BUS #2 |
|hcd_release |
|shared_hcd(kref=0)|
| |
-X-(cut off)-bandXX_mutex|
| |__________________|
|
___________________ |
|<4> | |
|dwc3_otg_sm_work | |
|usb_put_hcd | |
|primary_hcd(kref=1)| |
|___________________| |
_________|_________ |
|<5> | |
|New USB BUS #1 | |
|hcd_release | |
|primary_hcd(kref=0)| |
| | |
|bandXX_mutex(free) |<-
|___________________|
=================================================
>
>> ==============================================
>> At *remove USB(3.0) Storage
>> sequence <1> --> <5> ((Normal Case))
>> ==============================================
>> VOLD
>> =================================|============
>> (uevent)
>> ______|___________
>> |<1> |
>> | SCSI |
>> |usb_put_hcd |
>> |shared_hcd(kref=2)|
>> |__________________|
>> ___________________ ________|_________
>> |<4> | |<2> |
>> |dwc3_otg_sm_work | |dwc3_otg_sm_work |
>> |usb_put_hcd | |usb_put_hcd |
>> |primary_hcd(kref=1)| |shared_hcd(kref=1)|
>> |___________________| |__________________|
>> _________|_________ ________|_________
>> |<5> | |<3> |
>> |New USB BUS #1 | |New USB BUS #2 |
>> |hcd_release | |hcd_release |
>> |primary_hcd(kref=0)| |shared_hcd(kref=0)|
>> | | | |
>> |bandXX_mutex(free) | -X-cut off)-bandXX_mutex|
>> |___________________| |__________________|
>>
>> ----------------------------------------------
>
>> >The real bug here is that the shared_hcd is released after the
>> >primary_hcd. That's what you need to fix.
>>
>> NO, It 's only depend on vold(scsi) release time.
>> If the vold later released and is being released first hcd,
>> Double free happened at <5> as below.
>>
>> ==============================================
>> At *remove USB(3.0) Storage
>> sequence <1> --> <5> ((Problem Case))
>> ==============================================
>> VOLD
>> =================================|============
>> (uevent)
>> ______|___________
>> |<5> |
>> | SCSI |
>> |usb_put_hcd |
>> |shared_hcd(kref=0)|
>> |*hcd_release |
>> |bandXX_mutex(free*)|<- double free
>> |__________________|
>> ___________________ ________|_________
>> |<3> | |<1> |
>> |dwc3_otg_sm_work | |dwc3_otg_sm_work |
>> |usb_put_hcd | |usb_put_hcd |
>> |primary_hcd(kref=1)| |shared_hcd(kref=2)|
>> |___________________| |__________________|
>> _________|_________ ________|_________
>> |<4> | |<2> |
>> |New USB BUS #1 | |New USB BUS #2 |
>> |hcd_release | | |
>> |primary_hcd(kref=0)| |shared_hcd(kref=1)|
>> | | | |
>> |bandXX_mutex(free) |<-(Link)-bandXX_mutex |
>> |___________________| |__________________|
>>
>> ----------------------------------------------
>
>That's the same as what I said. In your diagram, vold releases the
>shared_hcd (in <5>) after dwc3_otg_sm_work releases the primary_hcd
>(in <4>).
>
=================================================
At *remove USB(3.0) Storage
sequence <1> --> <5> ((Problem Case))
=================================================
VOLD
------------------------------------|------------
(uevent)
________|_________
|<1> |
|dwc3_otg_sm_work |
|usb_put_hcd |
|shared_hcd(kref=2)|
|__________________|
________|_________
|<2> |
|New USB BUS #2 |
| |
|shared_hcd(kref=1)|
| |
--(Link)-bandXX_mutex|
| |__________________|
|
___________________ |
|<3> | |
|dwc3_otg_sm_work | |
|usb_put_hcd | |
|primary_hcd(kref=1)| |
|___________________| |
_________|_________ |
|<4> | |
|New USB BUS #1 | |
|hcd_release | |
|primary_hcd(kref=0)| |
| | |
|bandXX_mutex(free) |<-
|___________________|
(( VOLD ))
______|___________
|<5> |
| SCSI |
|usb_put_hcd |
|shared_hcd(kref=0)|
|*hcd_release |
|bandXX_mutex(free*)|<- double free
|__________________|
=================================================
>If you change the code so that the shared_hcd takes a reference to the
>primary_hcd and drops that reference when the shared_hcd is released,
>this will never occur.
>
>Alan Stern
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