Re: [PATCH net] net: usb: cdc_ncm: reject negative chained NDP offsets

Greg Kroah-Hartman
2026-04-13T10:43:29Z

On Mon, Apr 13, 2026 at 10:36:19AM +0200, Oliver Neukum wrote:
>
>
> On 11.04.26 12:53, Greg Kroah-Hartman wrote:
> > cdc_ncm_rx_fixup() reads dwNextNdpIndex from each NDP32 to chain to the
> > next one. The 32-bit value from the device is stored into the signed
> > int ndpoffset so that means values with the high bit set become
>
> Well, then isn't the problem rather that you should not store an
> unsigned value in a signed variable?

No. well, yes. but no.

cdc_ncm_rx_verify_nth16() returns an int, and is negative if something
went wrong, so we need it that way, and then we need to check it, like
we properly do at the top of the loop, it's just that at the bottom of
the loop we also need to do the same exact thing.

So I really think this patch is the correct thing to do unless you want
to add another temp variable here just for the sign -> unsigned
transition and but that might be even messier.

thanks,

greg k-h