Re: usb/core: slab-out-of-bounds read in cdc_parse_cdc_header

[Greg Kroah-Hartman]

On Thu, Sep 21, 2017 at 03:51:44PM +0200, Andrey Konovalov wrote:
> On Thu, Sep 21, 2017 at 10:04 AM, Greg Kroah-Hartman
> <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
> > On Thu, Sep 21, 2017 at 09:31:54AM +0200, Greg Kroah-Hartman wrote:
> >> On Wed, Sep 20, 2017 at 04:45:08PM +0200, Andrey Konovalov wrote:
> >> > Hi!
> >> >
> >> > I've got the following crash while fuzzing the kernel with syzkaller.
> >> >
> >> > On commit ebb2c2437d8008d46796902ff390653822af6cc4 (Sep 18).
> >> >
> >> > It looks like cdc_parse_cdc_header() doesn't validate buflen before
> >> > accessing buffer[1], buffer[2] and so on. The only check present is
> >> > while (buflen > 0).
> >>
> >> Ugh, you are right, let me go work on a patch, thanks for the report...
> >
> > Here's a first cut at a fix for this.  I think this should solve it, but
> > it's early and my coffee has not fully kicked in...
> >
> > thanks,
> >
> > greg k-h
> > -----------------
> >
> > diff --git a/drivers/usb/core/message.c b/drivers/usb/core/message.c
> > index 4c38ea41ae96..028feaf01aa5 100644
> > --- a/drivers/usb/core/message.c
> > +++ b/drivers/usb/core/message.c
> > @@ -2069,6 +2069,10 @@ int cdc_parse_cdc_header(struct usb_cdc_parsed_header *hdr,
> >                         elength = 1;
> >                         goto next_desc;
> >                 }
> > +               if ((buflen < elength) || (elength < 2)) {
> 
> Hi Greg,
> 
> I think this should check (elength < 3), since we access both
> buffer[1] and buffer[2] after this check.

{sigh}  yes, you are right, counted this one wrong.

With this patch, updated one below, does it fix your crash?

thanks,

greg k-h


diff --git a/drivers/usb/core/message.c b/drivers/usb/core/message.c
index 4c38ea41ae96..028feaf01aa5 100644
--- a/drivers/usb/core/message.c
+++ b/drivers/usb/core/message.c
@@ -2069,6 +2069,10 @@ int cdc_parse_cdc_header(struct usb_cdc_parsed_header *hdr,
 			elength = 1;
 			goto next_desc;
 		}
+		if ((buflen < elength) || (elength < 3)) {
+			dev_err(&intf->dev, "invalid descriptor buffer length\n");
+			break;
+		}
 		if (buffer[1] != USB_DT_CS_INTERFACE) {
 			dev_err(&intf->dev, "skipping garbage\n");
 			goto next_desc;