From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Anant Thazhemadam <anant.thazhemadam@gmail.com>
Cc: devel@driverdev.osuosl.org,
syzbot+009f546aa1370056b1c2@syzkaller.appspotmail.com,
Ian Abbott <abbotti@mev.co.uk>,
linux-kernel-mentees@lists.linuxfoundation.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v3] staging: comedi: check validity of wMaxPacketSize of usb endpoints found
Date: Sat, 10 Oct 2020 12:37:23 +0200 [thread overview]
Message-ID: <20201010103723.GA1456353@kroah.com> (raw)
In-Reply-To: <20201010093519.GA981987@kroah.com>
On Sat, Oct 10, 2020 at 11:35:19AM +0200, Greg Kroah-Hartman wrote:
> On Sat, Oct 10, 2020 at 01:59:32PM +0530, Anant Thazhemadam wrote:
> > While finding usb endpoints in vmk80xx_find_usb_endpoints(), check if
> > wMaxPacketSize = 0 for the endpoints found.
> >
> > Some devices have isochronous endpoints that have wMaxPacketSize = 0
> > (as required by the USB-2 spec).
> > However, since this doesn't apply here, wMaxPacketSize = 0 can be
> > considered to be invalid.
> >
> > Reported-by: syzbot+009f546aa1370056b1c2@syzkaller.appspotmail.com
> > Tested-by: syzbot+009f546aa1370056b1c2@syzkaller.appspotmail.com
> > Signed-off-by: Anant Thazhemadam <anant.thazhemadam@gmail.com>
> > ---
> > Changes in v3:
> > * Correctly list version information
> >
> > Changes in v2:
> > * Fix coding style issue
> >
> > The error (as detected by syzbot) is generated in
> > vmk80xx_write_packet() (which is called in vmk80xx_reset_device()) when
> > it tries to assign devpriv->usb_tx_buf[0] = cmd.
> >
> > This NULL pointer dereference issue arises because
> > size = usb_endpoint_maxp(devpriv->ep_tx) = 0.
> >
> > This can be traced back to vmk80xx_find_usb_endpoints(), where the usb
> > endpoints are found, and assigned accordingly.
> > (For some more insight, in vmk80xx_find_usb_endpoints(),
> > if one of intf->cur_altsetting->iface_desc->endpoints' desc value = 0,
> > and consequently this endpoint is assigned to devpriv->ep_tx,
> > this issue gets triggered.)
> >
> > Checking if the wMaxPacketSize of an endpoint is invalid and returning
> > an error value accordingly, seems to fix the error.
> >
> > We could also alternatively perform this checking (if the size is 0 or not)
> > in vmk80xx_reset_device() itself, but it only seemed like covering up the issue
> > at that place, rather than fixing it, so I wasn't sure that was any better.
> >
> > However, if I'm not wrong, this might end up causing the probe to fail, and I'm
> > not sure if that's the right thing to do in cases like this, and if it isn't I'd
> > like some input on what exactly is the required course of action in cases like this.
> >
> > drivers/staging/comedi/drivers/vmk80xx.c | 3 +++
> > 1 file changed, 3 insertions(+)
> >
> > diff --git a/drivers/staging/comedi/drivers/vmk80xx.c b/drivers/staging/comedi/drivers/vmk80xx.c
> > index 65dc6c51037e..cb0a965d3c37 100644
> > --- a/drivers/staging/comedi/drivers/vmk80xx.c
> > +++ b/drivers/staging/comedi/drivers/vmk80xx.c
> > @@ -667,6 +667,9 @@ static int vmk80xx_find_usb_endpoints(struct comedi_device *dev)
> > if (!devpriv->ep_rx || !devpriv->ep_tx)
> > return -ENODEV;
> >
> > + if (!usb_endpoint_maxp(devpriv->ep_rx) || !usb_endpoint_maxp(devpriv->ep_tx))
> > + return -EINVAL;
> > +
> > return 0;
> > }
>
> Why not just rewrite vmk80xx_find_usb_endpoints() to use the
> usb_find_common_endpoints() or other helper functions like
> usb_find_bulk_in_endpoint() or others, so that this type of thing is
> checked there?
>
> Ah, wait, no, the packet size is not checked there, sorry, maybe that
> will not help out here. Is a bulk urb allowed to have a 0 size? If
> not, maybe we should just forbid that in the core? Time to go read the
> USB spec...
That being said, this patch is correct, I'll go queue it up now so that
it gets into 5.10-rc1.
thanks,
greg k-h
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prev parent reply other threads:[~2020-10-10 10:36 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-10 8:29 [PATCH v3] staging: comedi: check validity of wMaxPacketSize of usb endpoints found Anant Thazhemadam
2020-10-10 9:35 ` Greg Kroah-Hartman
2020-10-10 10:37 ` Greg Kroah-Hartman [this message]
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