Re: [PATCH] usb: gadget: provide interface for legacy gadgets to get UDC name

[Marek Szyprowski <m.szyprowski@samsung.com>]

Hello,

On 2016-02-08 12:31, Vegard Nossum wrote:
> On 02/08/2016 12:12 PM, Marek Szyprowski wrote:
>> Since commit 855ed04a3758b205e84b269f92d26ab36ed8e2f7 ("usb: gadget:
>> udc-core: independent registration of gadgets and gadget drivers") 
>> gadget
>> drivers can not assume that UDC drivers are already available on their
>> initialization. This broke the HACK, which was used in gadgetfs driver,
>> to get UDC controller name. This patch removes this hack and replaces it
>> by additional function in the UDC core (which is usefully only for 
>> legacy
>> drivers, please don't use it in the new code).
>>
>> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
>> ---
>> Vegard: Could you check if this patch fixes your issue with gadgetfs 
>> and NULL
>> pointer dereference?
>>
>> Best regards,
>> Marek Szyprowski
>> ---
>
> [snip patch]
>
> Thanks for the patch, I gave it a try.
>
> Firstly, it changes /dev/gadget/dummy_udc into /dev/gadget/dummy_udc.0
> so it may break some userspace expectations (I don't really know).

Right, thanks for pointing this issue.

>
> Secondly, I still get this crash which looks a lot like what I
> originally reported:
>
> kasan: GPF could be caused by NULL-ptr deref or user memory 
> accessgeneral protection fault: 0000 [#1] DEBUG_PAGEALLOC KASAN
> CPU: 0 PID: 35 Comm: afl-fuzz Not tainted 4.5.0-rc2 #1
> task: ffff8800003b6900 ti: ffff88000c840000 task.ti: ffff88000c840000
> RIP: 0010:[<ffffffff81388536>]  [<ffffffff81388536>] 
> __list_del_entry+0x86/0x1d0
> RSP: 0018:ffff88000c847da8  EFLAGS: 00010246
> RAX: dffffc0000000000 RBX: 0000000000000000 RCX: ffffffff81a13f08
> RDX: 0000000000000000 RSI: 0000000000000061 RDI: ffffffff81a13f10
> RBP: ffff88000c847dc0 R08: 0000000000000246 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
> R13: dffffc0000000000 R14: ffffffff81a13e40 R15: ffff88000c83c500
> FS:  00007ffff7ff2740(0000) GS:ffffffff8193f000(0000) 
> knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00007ffff78c53a0 CR3: 000000000c850000 CR4: 00000000001406b0
> Stack:
>  ffffffff81a13e40 ffffffff81a13f08 ffffffff81a118e0 ffff88000c847dd8
>  ffffffff8138868d ffffffff81a11638 ffff88000c847e10 ffffffff81523a5d
>  ffffffff817f62a0 ffff880000277a40 ffff88000c83c510 ffff88000c83c520
> Call Trace:
>  [<ffffffff8138868d>] list_del+0xd/0x70
>  [<ffffffff81523a5d>] usb_gadget_unregister_driver+0x11d/0x240
>  [<ffffffff81533c34>] dev_release+0x44/0x110
>  [<ffffffff811f0ccb>] __fput+0x11b/0x490
>  [<ffffffff811f10a9>] ____fput+0x9/0x10
>  [<ffffffff810c8881>] task_work_run+0xf1/0x190
>  [<ffffffff811ea9ea>] ? filp_close+0x8a/0xe0
>  [<ffffffff81001c3c>] exit_to_usermode_loop+0xec/0x100
>  [<ffffffff81002531>] syscall_return_slowpath+0x91/0xc0
>  [<ffffffff817a4389>] int_ret_from_sys_call+0x25/0x8f
> Code: c4 0f 84 94 00 00 00 48 b8 00 02 00 00 00 00 ad de 48 39 c3 0f 
> 84 a5 00 00 00 48 89 da 48 b8 00 00 00 00 00 fc ff df 48 c1 ea 03 <80> 
> 3c 02 00 0f 85 e8 00 00 00 4c 8b 03 4c 39 c1 0f 85 9b 00 00
> RIP  [<ffffffff81388536>] __list_del_entry+0x86/0x1d0
>  RSP <ffff88000c847da8>
> ---[ end trace 9a6416535ca1ec01 ]---
>
> I am more than happy to try other patches :-) Thanks,

Okay, now I managed to reproduce it and I've sent a fix for gadgetfs driver
a few minutes ago. When both patches are applied, no more issue should 
be observed.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland