Re: usb/wireless/rsi_91x: use-after-free write in __run_timers

[Andrey Konovalov]

On Mon, Sep 25, 2017 at 6:26 AM, Kalle Valo <kvalo@xxxxxxxxxxxxxx> wrote:
> Andrey Konovalov <andreyknvl@xxxxxxxxxx> writes:
>
>> I've got the following report while fuzzing the kernel with syzkaller.
>>
>> On commit 6e80ecdddf4ea6f3cd84e83720f3d852e6624a68 (Sep 21).
>>
>> ==================================================================
>> BUG: KASAN: use-after-free in __run_timers+0xc0e/0xd40
>> Write of size 8 at addr ffff880069f701b8 by task swapper/0/0
>>
>> CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.14.0-rc1-42311-g6e80ecdddf4e #234
>> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Bochs 01/01/2011
>
> [...]
>
>> Allocated by task 1845:
>>  save_stack_trace+0x1b/0x20 arch/x86/kernel/stacktrace.c:59
>>  save_stack+0x43/0xd0 mm/kasan/kasan.c:447
>>  set_track mm/kasan/kasan.c:459
>>  kasan_kmalloc+0xad/0xe0 mm/kasan/kasan.c:551
>>  kmem_cache_alloc_trace+0x11e/0x2d0 mm/slub.c:2772
>>  kmalloc ./include/linux/slab.h:493
>>  kzalloc ./include/linux/slab.h:666
>>  rsi_91x_init+0x98/0x510 drivers/net/wireless/rsi/rsi_91x_main.c:203
>>  rsi_probe+0xb6/0x13b0 drivers/net/wireless/rsi/rsi_91x_usb.c:665
>>  usb_probe_interface+0x35d/0x8e0 drivers/usb/core/driver.c:361
>
> I'm curious about your setup. Apparently you are running syzkaller on
> QEMU but what I don't understand is how the rsi device comes into the
> picture. Did you have a rsi usb device connected to the virtual machine
> or what? Or does syzkaller do some kind of magic here?

I use dummy_hcd and gadgetfs to connect random USB devices to the
kernel from a userspace application. This happens inside a QEMU
instance. This simplifies fuzzing, since everything is virtualized,
but the found bugs can be triggered on a real machine by connecting a
malicious USB device.

>
> --
> Kalle Valo
>
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