linux-kernel - Re: BUG: KASAN: use-after-free in xhci_trb_virt_to

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Date:   Wed, 8 Jan 2020 11:34:22 +0200
From:   Mathias Nyman <mathias.nyman@...ux.intel.com>
To:     Paul Menzel <pmenzel@...gen.mpg.de>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:     Greg KH <greg@...ah.com>, Mathias Nyman <mathias.nyman@...el.com>,
        linux-usb@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: BUG: KASAN: use-after-free in
 xhci_trb_virt_to_dma.part.24+0x1c/0x80

On 7.1.2020 17.35, Paul Menzel wrote:
> Dear Mathias, dear Mika,
> 
> 
> On 2020-01-07 13:09, Mathias Nyman wrote:
>> On 3.1.2020 13.04, Mika Westerberg wrote:
>>> On Thu, Jan 02, 2020 at 03:10:14PM +0100, Paul Menzel wrote:
>>>> Mika, as you fixed the other leak, any idea, how to continue from the
>>>> kmemleak log below?
>>>>
>>>> ```
>>>> unreferenced object 0xffff8c207a1e1408 (size 8):
>>>>     comm "systemd-udevd", pid 183, jiffies 4294667978 (age 752.292s)
>>>>     hex dump (first 8 bytes):
>>>>       34 01 05 00 00 00 00 00                          4.......
>>>>     backtrace:
>>>>       [<00000000aea7b46d>] xhci_mem_init+0xcfa/0xec0 [xhci_hcd]
>>>
>>> There are probably better ways for doing this but you can use objdump
>>> for example:
>>>
>>>     $ objdump -l --prefix-addresses -j .text --disassemble=xhci_mem_init drivers/usb/host/xhci-hcd.ko
>>>
>>> then find the offset xhci_mem_init+0xcfa. It should show you the line
>>> numbers as well if you have compiled your kernel with debug info. This
>>> should be close to the line that allocated the memory that was leaked.
> 
> Thank you. I actually remembered `script/f2addr2line`.
> 
>      $ scripts/faddr2line drivers/usb/host/xhci-hcd.o xhci_mem_init+0xcfa
>      xhci_mem_init+0xcfa/0xec0:
>      xhci_add_in_port at /mnt/drivers/usb/host/xhci-mem.c:2161
>      (inlined by) xhci_setup_port_arrays at /mnt/drivers/usb/host/xhci-mem.c:2309
>      (inlined by) xhci_mem_init at /mnt/drivers/usb/host/xhci-mem.c:2538
> 
>> Paul, it possible that your xhci controller has several
>> supported protocol extended capabilities for usb 3 ports, each
>> with their own custom protocol speed ID table.
>>
>> xhci driver assumes there is only one custome PSI table per roothub,
>> and we will end up allocating the second PSI table on top of the first,
>> leaking the first.
>>
>> Could you boot with xhci dynamic debug enabled, and show dmesg after boot, add:
>> xhci_hcd.dyndbg=+p
>> to you kernel cmdline.
>>
>> Or as an alternative, show output of:
>>
>> sudo cat /sys/kernel/debug/usb/xhci/*/reg-ext-protocol*
> 
> `/sys/kernel/debug/` cannot be read by unprivileged users, so the wildcard does
> not work with `sudo`.
> 
> ```
> $ sudo ls /sys/kernel/debug/usb/xhci
> 0000:12:00.0  0000:26:00.3  0000:26:00.4
> # cat /sys/kernel/debug/usb/xhci/*/reg-ext-protocol*

problematic xhci:
capability for first four USB 2 ports
> EXTCAP_REVISION = 0x02000402
> EXTCAP_NAME = 0x20425355
> EXTCAP_PORTINFO = 0x00180401
> EXTCAP_PORTTYPE = 0x00000000

capability for one USB 3.1 port (5th port)
> EXTCAP_REVISION = 0x03100802
> EXTCAP_NAME = 0x20425355
> EXTCAP_PORTINFO = 0x10000105
> EXTCAP_PORTTYPE = 0x00000000
> EXTCAP_MANTISSA1 = 0x00050134
capability for one USB 3.1 port (6th port)
> EXTCAP_REVISION = 0x03100802
> EXTCAP_NAME = 0x20425355
> EXTCAP_PORTINFO = 0x10000106
> EXTCAP_PORTTYPE = 0x00000000
> EXTCAP_MANTISSA1 = 0x00050134
capability for one USB 3.1 port (7th port)
> EXTCAP_REVISION = 0x03100802
> EXTCAP_NAME = 0x20425355
> EXTCAP_PORTINFO = 0x10000107
> EXTCAP_PORTTYPE = 0x00000000
> EXTCAP_MANTISSA1 = 0x00050134
capability for one USB 3.1 port (8th port)
> EXTCAP_REVISION = 0x03100802
> EXTCAP_NAME = 0x20425355
> EXTCAP_PORTINFO = 0x10000108
> EXTCAP_PORTTYPE = 0x00000000
> EXTCAP_MANTISSA1 = 0x00050134

It has eight ports.  last four of them are USB 3.1 ports.
It has a very odd setup where each 3.1 port has their own
supported protocol capability with a custom PSI, but all the PSI's are similar,
telling the port only support a 5Gbps speed.

We leak all the custom PSI tables for USB 3.1 ports except the last,
these would be the EXTCAP_MANTISSA1 = 0x00050134, which is the same as
the hex dump of the unreferenced object you posted earlier (considering byte order):

hex dump (first 8 bytes):
34 01 05 00 00 00 00 00                          4.......

I'm working on a patch for this

-Mathias