Re: panic: invalid bcd xxx

On Tue, Feb 28, 2017 at 2:31 PM, Eric van Gyzen <vangyzen_at_freebsd.org> wrote:
> Your system's real-time clock is returning garbage.  r312702 added some
> input validation a few weeks ago.  Previously, the kernel was reading beyond
> the end of an array and either complaining about the clock or setting it to
> the wrong time based on whatever was in the memory beyond the array.
>
> The added validation shouldn't be an assertion because it operates on data
> beyond the kernel's control.  Try this:
>
> --- sys/libkern.h       (revision 314424)
> +++ sys/libkern.h       (working copy)
> _at__at_ -57,8 +57,10 _at__at_
>  bcd2bin(int bcd)
>  {
>
> -       KASSERT(bcd >= 0 && bcd < LIBKERN_LEN_BCD2BIN,
> -           ("invalid bcd %d", bcd));
> +       if (bcd < 0 || bcd >= LIBKERN_LEN_BCD2BIN) {
> +               printf("invalid bcd %d\n", bcd);
> +               return (0);
> +       }
>         return (bcd2bin_data[bcd]);
>  }

I don't think removing this assertion and truncating to zero is the
right thing to do.  Adding an error return to this routine is a little
much, though.  I think probably the caller should perform input
validation between the broken device and this routine.

Thanks,
Conrad