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* [PATCH 4.14] wireless: Use offsetof instead of custom macro.
@ 2020-07-31 21:03 Nick Desaulniers
  0 siblings, 0 replies; only message in thread
From: Nick Desaulniers @ 2020-07-31 21:03 UTC (permalink / raw)
  To: stable; +Cc: Pi-Hsun Shih, Johannes Berg, Nick Desaulniers

From: Pi-Hsun Shih <>

commit 6989310f5d4327e8595664954edd40a7f99ddd0d upstream.

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:
 ___cfg80211_scan_done+0x13c/0x220 [cfg80211]
 __cfg80211_scan_done+0x28/0x34 [cfg80211]

Signed-off-by: Pi-Hsun Shih <>
Reviewed-by: Nick Desaulniers <>
Signed-off-by: Johannes Berg <>
Signed-off-by: Nick Desaulniers <>
Fix landed in v5.7-rc1. Thanks to James Hsu of MediaTek for the report.

 include/uapi/linux/wireless.h | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/wireless.h b/include/uapi/linux/wireless.h
index 86eca3208b6b..a2c006a364e0 100644
--- a/include/uapi/linux/wireless.h
+++ b/include/uapi/linux/wireless.h
@@ -74,6 +74,8 @@
 #include <linux/socket.h>		/* for "struct sockaddr" et al	*/
 #include <linux/if.h>			/* for IFNAMSIZ and co... */
+#include <stddef.h>                     /* for offsetof */
 /***************************** VERSION *****************************/
  * This constant is used to know the availability of the wireless
@@ -1090,8 +1092,7 @@ 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) - \

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