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)
base-commit: 1875ff320f14afe21731a6e4c7b46dd33e45dfaa
--
2.24.0.393.g34dc348eaf-goog
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)
On Thu, Nov 28, 2019 at 11:54 AM Joe Perches <[email protected]> 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.
>