Re: [Patch 1/1] wext: fix 32/64 bit alignment issue for 'point' type

[Johannes Berg <johannes@sipsolutions.net>]

On Thu, 2010-09-30 at 16:38 +0200, Johannes Berg wrote:
> On Thu, 2010-09-30 at 12:25 +0200, Gerrit Renker wrote:
> > wireless: fix alignment problem
> > 
> > With the current definition, IW_EV_POINT_PK_LEN is 12 on 64-bit and 8 on 32-bit systems,
> > due to the way struct iw_event is packed (24 byte on 64-bit systems instead of 20 byte
> > on 32-bit systems). Furthermore, the iwe_stream_add_point() in include/net/iw_handler.h
> > also uses IW_EV_LCP_PK_LEN as header length. 
> > 
> > The current definition appears to be a typo (PK_LEN instead of LEN); it causes 
> > misalignment on 64 bit systems.
> 
> So, correct me if I'm wrong, the only effect this change has is changing
> the second memcpy() in iwe_stream_add_point() to not copy an extra 4
> bytes that will be overwritten right away by the next memcpy()
> (presumably, unless the data is < 4, in which case the memcpy might
> actually be out of bounds).

Interestingly -- yay for wext! -- wireless-tools source code actually
uses the define you propose:

#define IW_EV_POINT_PK_LEN	(IW_EV_LCP_PK_LEN + 4)

which probably means that it was fixed there but the fix never
propagated to the kernel ...

johannes