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 <[email protected]>
---
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
On Thu, Apr 18, 2019 at 3:50 PM Pi-Hsun Shih <[email protected]> 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 <[email protected]>
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 <[email protected]>
> ---
> 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
>