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* [PATCH RESEND] wireless: Use offsetof instead of custom macro.
@ 2019-11-28  3:39 Pi-Hsun Shih
  2019-11-28  3:53 ` Joe Perches
  0 siblings, 1 reply; 4+ messages in thread
From: Pi-Hsun Shih @ 2019-11-28  3:39 UTC (permalink / raw)
  To: unlisted-recipients:; (no To-header on input)
  Cc: Pi-Hsun Shih, linux-wireless, Johannes Berg, linux-kernel,
	clang-built-linux

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@chromium.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)
 

base-commit: 1875ff320f14afe21731a6e4c7b46dd33e45dfaa
-- 
2.24.0.393.g34dc348eaf-goog


^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [PATCH RESEND] wireless: Use offsetof instead of custom macro.
  2019-11-28  3:39 [PATCH RESEND] wireless: Use offsetof instead of custom macro Pi-Hsun Shih
@ 2019-11-28  3:53 ` Joe Perches
  2019-11-29  4:04   ` Pi-Hsun Shih
  0 siblings, 1 reply; 4+ messages in thread
From: Joe Perches @ 2019-11-28  3:53 UTC (permalink / raw)
  To: Pi-Hsun Shih
  Cc: linux-wireless, Johannes Berg, open list,
	open list:CLANG/LLVM BUILD SUPPORT

On Thu, 2019-11-28 at 11:39 +0800, Pi-Hsun Shih 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:
[]
> diff --git 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)

This is uapi.  Is offsetof guaranteed to be available?

Perhaps this is better without using another macro

#define IW_EV_POINT_OFF	((size_t)&((struct iw_point *)NULL)->length)


^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [PATCH RESEND] wireless: Use offsetof instead of custom macro.
  2019-11-28  3:53 ` Joe Perches
@ 2019-11-29  4:04   ` Pi-Hsun Shih
  2019-12-02 17:27     ` Nick Desaulniers
  0 siblings, 1 reply; 4+ messages in thread
From: Pi-Hsun Shih @ 2019-11-29  4:04 UTC (permalink / raw)
  To: Joe Perches
  Cc: linux-wireless, Johannes Berg, open list,
	open list:CLANG/LLVM BUILD SUPPORT

On Thu, Nov 28, 2019 at 11:54 AM Joe Perches <joe@perches.com> wrote:
>
> On Thu, 2019-11-28 at 11:39 +0800, Pi-Hsun Shih 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:
> []
> > diff --git 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)
>
> This is uapi.  Is offsetof guaranteed to be available?

offsetof is already used in other uapi headers
(include/uapi/linux/fuse.h FUSE_NAME_OFFSET).

Also offsetof is also defined back in C89 standard (in stddef.h), so
it should be widely available and should be fine to use here?
(Should I add a #ifndef __KERNEL__ #include <stddef.h> to the file?)

>
> Perhaps this is better without using another macro
>
> #define IW_EV_POINT_OFF ((size_t)&((struct iw_point *)NULL)->length)

Clang UBSAN would still complain about this, since it's the same
pattern as the original one.

>

^ permalink raw reply	[flat|nested] 4+ messages in thread

* Re: [PATCH RESEND] wireless: Use offsetof instead of custom macro.
  2019-11-29  4:04   ` Pi-Hsun Shih
@ 2019-12-02 17:27     ` Nick Desaulniers
  0 siblings, 0 replies; 4+ messages in thread
From: Nick Desaulniers @ 2019-12-02 17:27 UTC (permalink / raw)
  To: Pi-Hsun Shih
  Cc: Joe Perches, linux-wireless, Johannes Berg, open list,
	open list:CLANG/LLVM BUILD SUPPORT

On Thu, Nov 28, 2019 at 8:05 PM Pi-Hsun Shih <pihsun@chromium.org> wrote:
>
> On Thu, Nov 28, 2019 at 11:54 AM Joe Perches <joe@perches.com> wrote:
> >
> > On Thu, 2019-11-28 at 11:39 +0800, Pi-Hsun Shih 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:
> > []
> > > diff --git 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)
> >
> > This is uapi.  Is offsetof guaranteed to be available?
>
> offsetof is already used in other uapi headers
> (include/uapi/linux/fuse.h FUSE_NAME_OFFSET).
>
> Also offsetof is also defined back in C89 standard (in stddef.h), so
> it should be widely available and should be fine to use here?
> (Should I add a #ifndef __KERNEL__ #include <stddef.h> to the file?)

Yes, please, otherwise userspace could have a
-Wimplicit-function-definition warning from including this header,
since it would look like a function call to a previously undeclared
function.

Actually, it looks like include/uapi/linux/posix_types.h includes it
unconditionally, and many other headers under include/uapi/ include
include/uapi/linux/posix_types.h (unconditionally).  So it may be ok
to just include stddef.h unconditionally, but please do so in addition
to the current diff you have.

-- 
Thanks,
~Nick Desaulniers

^ permalink raw reply	[flat|nested] 4+ messages in thread

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Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2019-11-28  3:39 [PATCH RESEND] wireless: Use offsetof instead of custom macro Pi-Hsun Shih
2019-11-28  3:53 ` Joe Perches
2019-11-29  4:04   ` Pi-Hsun Shih
2019-12-02 17:27     ` Nick Desaulniers

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