linux-kernel - Re: [PATCH] wireless: Use offsetof instead of custom macro.

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Date:   Wed, 27 Nov 2019 15:39:58 -0800
From:   Brian Norris <briannorris@...omium.org>
To:     Nicolas Boichat <drinkcat@...omium.org>
Cc:     Pi-Hsun Shih <pihsun@...omium.org>,
        open list <linux-kernel@...r.kernel.org>,
        linux-wireless@...r.kernel.org
Subject: Re: [PATCH] wireless: Use offsetof instead of custom macro.

+ linux-wireless

[Top-posting because the important stuff is up here, and the rest is
missing from linux-wireless]

Hey Pi-Hsun, Nicolas: you failed to copy linux-wireless, so no one's
going to pick this patch up. Please re-send if you care.

Regards,
Brian

On Thu, May 02, 2019 at 03:56:33PM +0800, Nicolas Boichat wrote:
> On Thu, Apr 18, 2019 at 3:50 PM Pi-Hsun Shih <pihsun@...omium.org> wrote:
> >
> > Use offsetof to calculate offset of a field to take advantage of
> > compiler built-in version when possible, and avoid UBSAN warning when
> > compiling with Clang:
> >
> > ==================================================================
> > UBSAN: Undefined behaviour in net/wireless/wext-core.c:525:14
> > member access within null pointer of type 'struct iw_point'
> > CPU: 3 PID: 165 Comm: kworker/u16:3 Tainted: G S      W         4.19.23 #43
> > Workqueue: cfg80211 __cfg80211_scan_done [cfg80211]
> > Call trace:
> >  dump_backtrace+0x0/0x194
> >  show_stack+0x20/0x2c
> >  __dump_stack+0x20/0x28
> >  dump_stack+0x70/0x94
> >  ubsan_epilogue+0x14/0x44
> >  ubsan_type_mismatch_common+0xf4/0xfc
> >  __ubsan_handle_type_mismatch_v1+0x34/0x54
> >  wireless_send_event+0x3cc/0x470
> >  ___cfg80211_scan_done+0x13c/0x220 [cfg80211]
> >  __cfg80211_scan_done+0x28/0x34 [cfg80211]
> >  process_one_work+0x170/0x35c
> >  worker_thread+0x254/0x380
> >  kthread+0x13c/0x158
> >  ret_from_fork+0x10/0x18
> > ===================================================================
> >
> > Signed-off-by: Pi-Hsun Shih <pihsun@...omium.org>
> 
> The warning from clang is spurious, but in another case, we felt that
> the cleanup was worth it, nevertheless
> (https://lore.kernel.org/patchwork/patch/1050040/).
> 
> Reviewed-By: Nicolas Boichat <drinkcat@...omium.org>
> 
> > ---
> >  include/uapi/linux/wireless.h | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/include/uapi/linux/wireless.h b/include/uapi/linux/wireless.h
> > index 86eca3208b6b..f259cca5cc2b 100644
> > --- a/include/uapi/linux/wireless.h
> > +++ b/include/uapi/linux/wireless.h
> > @@ -1090,8 +1090,7 @@ struct iw_event {
> >  /* iw_point events are special. First, the payload (extra data) come at
> >   * the end of the event, so they are bigger than IW_EV_POINT_LEN. Second,
> >   * we omit the pointer, so start at an offset. */
> > -#define IW_EV_POINT_OFF (((char *) &(((struct iw_point *) NULL)->length)) - \
> > -                         (char *) NULL)
> > +#define IW_EV_POINT_OFF offsetof(struct iw_point, length)
> >  #define IW_EV_POINT_LEN        (IW_EV_LCP_LEN + sizeof(struct iw_point) - \
> >                          IW_EV_POINT_OFF)
> >
> > --
> > 2.21.0.392.gf8f6787159e-goog
> >