linux-kernel - Re: [PATCH] usb: mtu3: Fix possible use-before-initialization bug

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Message-ID: <20230711114155.4a000704@bootlin.com>
Date:   Tue, 11 Jul 2023 11:41:55 +0200
From:   Herve Codina <herve.codina@...tlin.com>
To:     "Chunfeng Yun (云春峰)" <Chunfeng.Yun@...iatek.com>
Cc:     "yhao016@....edu" <yhao016@....edu>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>
Subject: Re: [PATCH] usb: mtu3: Fix possible use-before-initialization bug

Hi Chunfeng,

On Tue, 11 Jul 2023 08:48:35 +0000
Chunfeng Yun (云春峰) <Chunfeng.Yun@...iatek.com> wrote:

> On Mon, 2023-07-10 at 08:25 +0200, Herve Codina wrote:
> >  	 
> > External email : Please do not click links or open attachments until
> > you have verified the sender or the content.
> >  Hi Yu,
> > 
> > On Sun, 9 Jul 2023 17:48:15 -0700
> > Yu Hao <yhao016@....edu> wrote:
> >   
> > > Hi Hervé,
> > > 
> > > Thanks for the comments. How about this patch?
> > > ---
> > >  drivers/usb/mtu3/mtu3_gadget_ep0.c | 11 ++++++++---
> > >  1 file changed, 8 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/drivers/usb/mtu3/mtu3_gadget_ep0.c
> > > b/drivers/usb/mtu3/mtu3_gadget_ep0.c
> > > index e4fd1bb14a55..af2884943c2a 100644
> > > --- a/drivers/usb/mtu3/mtu3_gadget_ep0.c
> > > +++ b/drivers/usb/mtu3/mtu3_gadget_ep0.c
> > > @@ -600,7 +600,7 @@ static void ep0_tx_state(struct mtu3 *mtu)
> > >         mtu3_readl(mtu->mac_base, U3D_EP0CSR));
> > >  }
> > > 
> > > -static void ep0_read_setup(struct mtu3 *mtu, struct  
> > usb_ctrlrequest *setup)  
> > > +static int ep0_read_setup(struct mtu3 *mtu, struct usb_ctrlrequest  
> > *setup)  
> > >  {
> > >     struct mtu3_request *mreq;
> > >     u32 count;
> > > @@ -608,6 +608,8 @@ static void ep0_read_setup(struct mtu3 *mtu,
> > > struct usb_ctrlrequest *setup)
> > > 
> > >     csr = mtu3_readl(mtu->mac_base, U3D_EP0CSR) & EP0_W1C_BITS;
> > >     count = mtu3_readl(mtu->mac_base, U3D_RXCOUNT0);
> > > +   if (count == 0)
> > > +       return -EINVAL;  
> > 
> > 'count' should be tested against sizeof(*setup). Indeed, we need to
> > have a
> > setup data packet in the fifo.
> > 
> > What do you think about:
> > if (count < sizef(*setup))
> > return -EINVAL;  
> before call this function, already check the data length in fifo, it
> should be 8 bytes.
> see mtu3_ep0_isr(), about line 761.

Indeed, I missed that point.
Thanks for pointing it.

Regards,
Hervé

> 
> I think no need this patch
> 
> Thanks a lot
> 
> >   
> > > 
> > >     ep0_read_fifo(mtu->ep0, (u8 *)setup, count);
> > > 
> > > @@ -642,7 +644,8 @@ __acquires(mtu->lock)
> > >     struct mtu3_request *mreq;
> > >     int handled = 0;
> > > 
> > > -   ep0_read_setup(mtu, &setup);
> > > +   if (ep0_read_setup(mtu, &setup))
> > > +       return -EINVAL;  
> > 
> > Forward the error code to the caller ?
> > 
> > ret = ep0_read_setup(mtu, &setup)
> > if (ret < 0)
> > return ret;
> > 
> >   
> > >     trace_mtu3_handle_setup(&setup);
> > > 
> > >     if ((setup.bRequestType & USB_TYPE_MASK) == USB_TYPE_STANDARD)
> > > @@ -764,7 +767,9 @@ irqreturn_t mtu3_ep0_isr(struct mtu3 *mtu)
> > >             break;
> > >         }
> > > 
> > > -       ep0_handle_setup(mtu);
> > > +       if (ep0_handle_setup(mtu))
> > > +           break;
> > > +  
> > 
> > Ok
> >   
> > >         ret = IRQ_HANDLED;
> > >         break;
> > >     default:  
> > 
> > Be careful, your patch is wrongly indented.
> > tabs replaced by 4 spaces. You need to keep tabs.
> > 
> > Regards,
> > Hervé Codina
> >