Re: mysterious -1 offset in staging rt2860 driver

[Darren Jenkins <darrenrjenkins@gmail.com>]

On Fri, Mar 5, 2010 at 6:14 AM, Dan Carpenter <error27@gmail.com> wrote:
> So here is a mystery for people who enjoy such mysterious things.
>
> drivers/staging/rt2860/sta_ioctl.c +1020 rt_ioctl_giwscan(219)
>  1011                  if (CAP_IS_PRIVACY_ON
>  1012                      (pAdapter->ScanTab.BssEntry[i].CapabilityInfo))
>  1013                          iwe.u.data.flags = IW_ENCODE_ENABLED | IW_ENCODE_NOKEY;
>  1014                  else
>  1015                          iwe.u.data.flags = IW_ENCODE_DISABLED;
>  1016
>  1017                  __smatch_value("iwe.u.data.flags");
>  1018                  previous_ev = current_ev;
>  1019                  current_ev >  1020                      iwe_stream_add_point(info, current_ev, end_buf, &iwe,
>  1021                                           (char *)pAdapter->
>  1022                                           SharedKey[BSS0][(iwe.u.data.
>  1023                                                            flags &
>  1024                                                            IW_ENCODE_INDEX) -
>  1025                                                           1].Key);
>
>
> That last bit is easier to read if it's on one line.
>
> SharedKey[BSS0][(iwe.u.data.flags & IW_ENCODE_INDEX) - 1].Key);
>
> iwe.u.data.flags is either 0x0400 or 0x8000.  IW_ENCODE_INDEX is 0xff, so
> after we mask off the lower bits we get 0x00 and then we subtract 1 we get
> an array offset of -1.
>
> I doubt that's what we want, but what _do_ we want here?
>

Looking at the use of IW_ENCODE_INDEX elsewhere it seems to be a mask
for a key value that can be 0..4 where 0 means some default value and
1 - 4 means use value-- ie 0 - 3.

iwe.u.data.flags is assigned to 1 earlier so I would assume the code should be

                                iwe.u.data.flags  &= ~ IW_ENCODE_FLAGS
>>   1011                  if (CAP_IS_PRIVACY_ON
>>   1012                      (pAdapter->ScanTab.BssEntry[i].CapabilityInfo))
>>   1013                          iwe.u.data.flags |= IW_ENCODE_ENABLED | IW_ENCODE_NOKEY;
>>   1014                  else
>>   1015                          iwe.u.data.flags |= IW_ENCODE_DISABLED;

Which I think would both make sense and give an array index of 0.


Darren J.
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