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SubjectRe: [PATCH] USB: s2255 & stkwebcam: fix oops with malicious USB descriptors
On Tue, Apr 16, 2019 at 01:26:45PM +0200, Johan Hovold wrote:
> On Thu, Apr 11, 2019 at 12:54:12PM +0800, Young Xiao wrote:
> > From: Young Xiao <YangX92@hotmail.com>
> >
> > The driver expects at least one valid endpoint. If given
> > malicious descriptors that specify 0 for the number of endpoints,
> > it will crash in the probe function. Ensure there is at least
> > one endpoint on the interface before using it.
>
> Why do claim it will crash?

Ok, I see now that Björn already pointed this out to you in your
updated version of this patch.

> > This vulnerability is same as CVE-2016-2188.
>
> Note that the "fix" for this CVE that you're now copying was incomplete.
> Here's the proper fix:
>
> b7321e81fc36 ("USB: iowarrior: fix NULL-deref at probe")
>
> > Signed-off-by: Young Xiao <YangX92@hotmail.com>
> > ---
> > drivers/media/usb/s2255/s2255drv.c | 7 +++++++
> > drivers/media/usb/stkwebcam/stk-webcam.c | 6 ++++++
> > 2 files changed, 13 insertions(+)
> >
> > diff --git a/drivers/media/usb/s2255/s2255drv.c b/drivers/media/usb/s2255/s2255drv.c
> > index 5b3e54b..7fdf159 100644
> > --- a/drivers/media/usb/s2255/s2255drv.c
> > +++ b/drivers/media/usb/s2255/s2255drv.c
> > @@ -2263,6 +2263,13 @@ static int s2255_probe(struct usb_interface *interface,
> > iface_desc = interface->cur_altsetting;
> > dev_dbg(&interface->dev, "num EP: %d\n",
> > iface_desc->desc.bNumEndpoints);
> > +
> > + if (iface_desc->desc.bNumEndpoints < 1) {
> > + dev_err(&interface->dev, "Invalid number of endpoints\n");
> > + retval = -EINVAL;
> > + goto error;
> > + }
> > +
> > for (i = 0; i < iface_desc->desc.bNumEndpoints; ++i) {
>
> Besides that you didn't even bother compile-testing this, there is no
> bug here to fix to begin with.
>
> If bNumEndpoints is zero this loop will execute and the driver bails out
> just after since dev->read_endpoint is NULL.

That was meant to read "will never execute".

Johan

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