From: Karsten Keil <kkeil@suse.de>

I found a bug in the PPPIOCSPASS PPPIOCSACTIVE IOCTL implementation in
kernel 2.5/2.6.

The current pppd code use a empty filter (uprog.len=0) to detach the filter
in the kernel, but this code was removed in 2.5.71 while fixing a compiler
warning.

Here the new patch, also with better limit checking.

The second patch check for flen == 0 in the filter check too, since later
in this code a filter[flen - 1] access is done, which is not so funny with
flen 0.  Maybe it's not really needed anymore, since with the first patch
it would not longer called with flen=0.

paulus says:

    It looks correct.  Previously we had (and in 2.4 we still have)

        if (uprog.len > 0 && uprog.len < 65536) {
		...

    which gave warnings since uprog.len is unsigned short.  So someone
    decided that both parts of the condition were redundant.