[PATCH] staging: rtl8723bs: Check for NULL header value

[Kees Cook]

When building with -Warray-bounds, the following warning is emitted:

In file included from ./include/linux/string.h:253,
                 from ./arch/x86/include/asm/page_32.h:22,
                 from ./arch/x86/include/asm/page.h:14,
                 from ./arch/x86/include/asm/thread_info.h:12,
                 from ./include/linux/thread_info.h:60,
                 from ./arch/x86/include/asm/preempt.h:7,
                 from ./include/linux/preempt.h:78,
                 from ./include/linux/rcupdate.h:27,
                 from ./include/linux/rculist.h:11,
                 from ./include/linux/sched/signal.h:5,
                 from ./drivers/staging/rtl8723bs/include/drv_types.h:17,
                 from drivers/staging/rtl8723bs/core/rtw_recv.c:7:
In function 'memcpy',
    inlined from 'wlanhdr_to_ethhdr' at drivers/staging/rtl8723bs/core/rtw_recv.c:1554:2:
./include/linux/fortify-string.h:41:33: warning: '__builtin_memcpy' offset [0, 5] is out of the bounds [0, 0] [-Warray-bounds]
   41 | #define __underlying_memcpy     __builtin_memcpy
      |                                 ^

This is because the compiler sees it is possible for "ptr" to be a NULL
value, and concludes that it has zero size and attempts to copy to it
would overflow. Instead, detect the NULL return and error out early.

Cc: Larry Finger <Larry.Finger@xxxxxxxxxxxx>
Cc: Phillip Potter <phil@xxxxxxxxxxxxxxxx>
Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
Cc: Michael Straube <straube.linux@xxxxxxxxx>
Cc: Fabio Aiuto <fabioaiuto83@xxxxxxxxx>
Cc: linux-staging@xxxxxxxxxxxxxxx
Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
---
 drivers/staging/rtl8723bs/core/rtw_recv.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/staging/rtl8723bs/core/rtw_recv.c b/drivers/staging/rtl8723bs/core/rtw_recv.c
index 41bfca549c64..61135c49322b 100644
--- a/drivers/staging/rtl8723bs/core/rtw_recv.c
+++ b/drivers/staging/rtl8723bs/core/rtw_recv.c
@@ -1513,6 +1513,9 @@ static signed int wlanhdr_to_ethhdr(union recv_frame *precvframe)
 	u8 *ptr = get_recvframe_data(precvframe) ; /*  point to frame_ctrl field */
 	struct rx_pkt_attrib *pattrib = &precvframe->u.hdr.attrib;
 
+	if (!ptr)
+		return _FAIL;
+
 	if (pattrib->encrypt)
 		recvframe_pull_tail(precvframe, pattrib->icv_len);
 
-- 
2.30.2