linux-kernel - RE: [PATCH v2] usb: gadget: composite: Fix null pointer exception

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Date:   Mon, 8 Nov 2021 13:10:14 +0000
From:   胡启航(Nick Hu) <huqihang@...o.com>
To:     Greg KH <gregkh@...uxfoundation.org>
CC:     "balbi@...nel.org" <balbi@...nel.org>,
        "peter.chen@...nel.org" <peter.chen@...nel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v2] usb: gadget: composite: Fix null pointer exception

> -----Original Message-----
> From: Greg KH <gregkh@...uxfoundation.org>
> Sent: Monday, November 8, 2021 8:56 PM
> To: 胡启航(Nick Hu) <huqihang@...o.com>
> Cc: balbi@...nel.org; peter.chen@...nel.org; linux-usb@...r.kernel.org;
> linux-kernel@...r.kernel.org
> Subject: Re: [PATCH v2] usb: gadget: composite: Fix null pointer exception
> 
> On Mon, Nov 08, 2021 at 12:42:24PM +0000, 胡启航(Nick Hu) wrote:
> > > -----Original Message-----
> > > From: Greg KH <gregkh@...uxfoundation.org>
> > > Sent: Friday, November 5, 2021 8:45 PM
> > > To: 胡启航(Nick Hu) <huqihang@...o.com>
> > > Cc: balbi@...nel.org; peter.chen@...nel.org;
> > > linux-usb@...r.kernel.org; linux-kernel@...r.kernel.org
> > > Subject: Re: [PATCH v2] usb: gadget: composite: Fix null pointer
> > > exception
> > >
> > > On Fri, Nov 05, 2021 at 06:48:40PM +0800, Qihang Hu wrote:
> > > > In the config_ep_by_speed_and_alt function, select the
> > > > corresponding descriptor through g->speed, but the function driver
> > > > may not support the corresponding speed. So, we need to check
> > > > whether the function driver provides the corresponding speed
> > > > descriptor when selecting the descriptor.
> > > >
> > > > [  237.708146]  android_work: sent uevent USB_STATE=CONNECTED [
> > > > 237.712464]  kconfigfs-gadget gadget: super-speed config #1: b [
> > > > 237.712487]  kUnable to handle kernel NULL pointer dereference at
> > > virtual address 0000000000000000
> > >
> > > So this is an invalid driver causing this problem?  Or can this be
> > > triggered by userspace?
> >
> > Yes, if the kernel is loaded with an interface driver that does not
> > support all speeds, this problem can be triggered in userspace.
> 
> What in-kernel driver does not support all speeds that can trigger this?
> 
> Why not fix the drivers?

This problem is caused by android f_audio_source.c
I think the core driver code should be improved to make it less susceptible to function-driven influence. 
Of course, repairing the function driver is the fundamental solution to the problem.

> > > > [  237.712493]  kMem abort info:
> > > > [  237.712498]  k  ESR = 0x96000006 [  237.712504]  k  EC = 0x25:
> > > > DABT (current EL), IL = 32 bits [  237.712510]  k  SET = 0, FnV =
> > > > 0 [  237.712515]  k  EA = 0, S1PTW = 0 [  237.712520]  kData abort
> > > > info:
> > > > [  237.712525]  k  ISV = 0, ISS = 0x00000006 [  237.712530]  k  CM
> > > > = 0, WnR = 0 [  237.712536]  kuser pgtable: 4k pages, 39-bit VAs,
> > > pgdp=000000020ef29000
> > > > [  237.712541]  k[0000000000000000] pgd=000000020ef2a003,
> > > pud=000000020ef2a003, pmd=0000000000000000
> > > > [  237.712554]  kInternal error: Oops: 96000006 [#1] PREEMPT SMP [
> > > > 237.722067]  kSkip md ftrace buffer dump for: 0x1609e0 [
> > > > 237.787037]  kWorkqueue: dwc_wq dwc3_bh_work.cfi_jt
> [  237.854922]
> > > > kpstate: 60c00085 (nZCv daIf +PAN +UAO) [  237.863165]  kpc :
> > > > config_ep_by_speed_and_alt+0x90/0x308
> > > > [  237.871766]  klr : audio_set_alt+0x54/0x78 [  237.879108]  ksp
> > > > : ffffffc0104839e0
> > > >
> > > > Signed-off-by: Qihang Hu <huqihang@...o.com>
> > >
> > > What commit id does this fix?
> >
> > I have not submitted a BUG.
> > I will study and submit a BUG as soon as possible.
> 
> I do not understand what you mean by this.  I am asking what commit caused
> this problem so we can mark this one as fixing it.
> 

This is a problem with Android's driver code.
The kernel does not include it.

Thanks