linux-kernel - Re: [PATCH] usbip: Fix free of unallocated memory in vhci tx

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Date:   Tue, 22 Oct 2019 18:26:11 +0900
From:   Suwan Kim <suwan.kim027@...il.com>
To:     shuah <shuah@...nel.org>
Cc:     Julia Lawall <julia.lawall@...6.fr>, gregkh@...uxfoundation.org,
        linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
        valentina.manea.m@...il.com, kbuild test robot <lkp@...el.com>
Subject: Re: [PATCH] usbip: Fix free of
 unallocated memory in vhci tx

On Mon, Oct 21, 2019 at 01:28:54PM -0600, shuah wrote:
> On 10/21/19 9:08 AM, Julia Lawall wrote:
> > 
> > 
> > On Mon, 21 Oct 2019, Suwan Kim wrote:
> > 
> > > iso_buffer should be set to NULL after use and free in the while loop.
> > > In the case of isochronous URB in the while loop, iso_buffer is
> > > allocated and after sending it to server, buffer is deallocated. And
> > > then, if the next URB in the while loop is not a isochronous pipe,
> > > iso_buffer still holds the previously deallocated buffer address and
> > > kfree tries to free wrong buffer address.
> > > 
> > > Fixes: ea44d190764b (“usbip: Implement SG support to vhci-hcd and stub driver”)
> > > Reported-by: kbuild test robot <lkp@...el.com>
> > > Reported-by: Julia Lawall <julia.lawall@...6.fr>
> > > Signed-off-by: Suwan Kim <suwan.kim027@...il.com>
> > > ---
> > >   drivers/usb/usbip/vhci_tx.c | 1 +
> > >   1 file changed, 1 insertion(+)
> > > 
> > > diff --git a/drivers/usb/usbip/vhci_tx.c b/drivers/usb/usbip/vhci_tx.c
> > > index c3803785f6ef..b290e810d11b 100644
> > > --- a/drivers/usb/usbip/vhci_tx.c
> > > +++ b/drivers/usb/usbip/vhci_tx.c
> > > @@ -73,6 +73,7 @@ static int vhci_send_cmd_submit(struct vhci_device *vdev)
> > >   		memset(&pdu_header, 0, sizeof(pdu_header));
> > >   		memset(&msg, 0, sizeof(msg));
> > >   		memset(&iov, 0, sizeof(iov));
> > > +		iso_buffer = NULL;
> > 
> > Somehow I would have put it after the kfree, since the kfree makes the
> > value invalid.  iso_buffer is already initialized to NULL for the first
> > iteration.  If you want to put the setting to NULL at the top of the loop,
> > maybe the = NULL in the first line should be removed.
> > 
> 
> It makes sense to clear it after kfree() on line 150.
> 
> This kfree() and clearing iso_buffer are necessary only for
> PIPE_ISOCHRONOUS case.
> 
> Please add a comment above that this is for isoc case.

Ok. I will send v2.

Regards
Suwan Kim