cfg80211: fix callback type mismatches in wext-compat

Instead of casting callback functions to type iw_handler, which trips
indirect call checking with Clang's Control-Flow Integrity (CFI), add
stub functions with the correct function type for the callbacks.
Reported-by: Sedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: Sami Tolvanen <samitolvanen@google.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20201117205902.405316-1-samitolvanen@google.comSigned-off-by: Johannes Berg <johannes.berg@intel.com>

net/wireless/wext-compat.c

@@ -1421,39 +1421,78 @@ static int cfg80211_wext_siwpmksa(struct net_device *dev,
 	}
 }
 
+#define DEFINE_WEXT_COMPAT_STUB(func, type)			\
+	static int __ ## func(struct net_device *dev,		\
+			      struct iw_request_info *info,	\
+			      union iwreq_data *wrqu,		\
+			      char *extra)			\
+	{							\
+		return func(dev, info, (type *)wrqu, extra);	\
+	}
+
+DEFINE_WEXT_COMPAT_STUB(cfg80211_wext_giwname, char)
+DEFINE_WEXT_COMPAT_STUB(cfg80211_wext_siwfreq, struct iw_freq)
+DEFINE_WEXT_COMPAT_STUB(cfg80211_wext_giwfreq, struct iw_freq)
+DEFINE_WEXT_COMPAT_STUB(cfg80211_wext_siwmode, u32)
+DEFINE_WEXT_COMPAT_STUB(cfg80211_wext_giwmode, u32)
+DEFINE_WEXT_COMPAT_STUB(cfg80211_wext_giwrange, struct iw_point)
+DEFINE_WEXT_COMPAT_STUB(cfg80211_wext_siwap, struct sockaddr)
+DEFINE_WEXT_COMPAT_STUB(cfg80211_wext_giwap, struct sockaddr)
+DEFINE_WEXT_COMPAT_STUB(cfg80211_wext_siwmlme, struct iw_point)
+DEFINE_WEXT_COMPAT_STUB(cfg80211_wext_giwscan, struct iw_point)
+DEFINE_WEXT_COMPAT_STUB(cfg80211_wext_siwessid, struct iw_point)
+DEFINE_WEXT_COMPAT_STUB(cfg80211_wext_giwessid, struct iw_point)
+DEFINE_WEXT_COMPAT_STUB(cfg80211_wext_siwrate, struct iw_param)
+DEFINE_WEXT_COMPAT_STUB(cfg80211_wext_giwrate, struct iw_param)
+DEFINE_WEXT_COMPAT_STUB(cfg80211_wext_siwrts, struct iw_param)
+DEFINE_WEXT_COMPAT_STUB(cfg80211_wext_giwrts, struct iw_param)
+DEFINE_WEXT_COMPAT_STUB(cfg80211_wext_siwfrag, struct iw_param)
+DEFINE_WEXT_COMPAT_STUB(cfg80211_wext_giwfrag, struct iw_param)
+DEFINE_WEXT_COMPAT_STUB(cfg80211_wext_siwretry, struct iw_param)
+DEFINE_WEXT_COMPAT_STUB(cfg80211_wext_giwretry, struct iw_param)
+DEFINE_WEXT_COMPAT_STUB(cfg80211_wext_siwencode, struct iw_point)
+DEFINE_WEXT_COMPAT_STUB(cfg80211_wext_giwencode, struct iw_point)
+DEFINE_WEXT_COMPAT_STUB(cfg80211_wext_giwpower, struct iw_param)
+DEFINE_WEXT_COMPAT_STUB(cfg80211_wext_siwpower, struct iw_param)
+DEFINE_WEXT_COMPAT_STUB(cfg80211_wext_siwgenie, struct iw_point)
+DEFINE_WEXT_COMPAT_STUB(cfg80211_wext_giwauth, struct iw_param)
+DEFINE_WEXT_COMPAT_STUB(cfg80211_wext_siwauth, struct iw_param)
+DEFINE_WEXT_COMPAT_STUB(cfg80211_wext_siwencodeext, struct iw_point)
+DEFINE_WEXT_COMPAT_STUB(cfg80211_wext_siwpmksa, struct iw_point)
+
 static const iw_handler cfg80211_handlers[] = {
-	[IW_IOCTL_IDX(SIOCGIWNAME)]	= (iw_handler) cfg80211_wext_giwname,
-	[IW_IOCTL_IDX(SIOCSIWFREQ)]	= (iw_handler) cfg80211_wext_siwfreq,
-	[IW_IOCTL_IDX(SIOCGIWFREQ)]	= (iw_handler) cfg80211_wext_giwfreq,
-	[IW_IOCTL_IDX(SIOCSIWMODE)]	= (iw_handler) cfg80211_wext_siwmode,
-	[IW_IOCTL_IDX(SIOCGIWMODE)]	= (iw_handler) cfg80211_wext_giwmode,
-	[IW_IOCTL_IDX(SIOCGIWRANGE)]	= (iw_handler) cfg80211_wext_giwrange,
-	[IW_IOCTL_IDX(SIOCSIWAP)]	= (iw_handler) cfg80211_wext_siwap,
-	[IW_IOCTL_IDX(SIOCGIWAP)]	= (iw_handler) cfg80211_wext_giwap,
-	[IW_IOCTL_IDX(SIOCSIWMLME)]	= (iw_handler) cfg80211_wext_siwmlme,
-	[IW_IOCTL_IDX(SIOCSIWSCAN)]	= (iw_handler) cfg80211_wext_siwscan,
-	[IW_IOCTL_IDX(SIOCGIWSCAN)]	= (iw_handler) cfg80211_wext_giwscan,
-	[IW_IOCTL_IDX(SIOCSIWESSID)]	= (iw_handler) cfg80211_wext_siwessid,
-	[IW_IOCTL_IDX(SIOCGIWESSID)]	= (iw_handler) cfg80211_wext_giwessid,
-	[IW_IOCTL_IDX(SIOCSIWRATE)]	= (iw_handler) cfg80211_wext_siwrate,
-	[IW_IOCTL_IDX(SIOCGIWRATE)]	= (iw_handler) cfg80211_wext_giwrate,
-	[IW_IOCTL_IDX(SIOCSIWRTS)]	= (iw_handler) cfg80211_wext_siwrts,
-	[IW_IOCTL_IDX(SIOCGIWRTS)]	= (iw_handler) cfg80211_wext_giwrts,
-	[IW_IOCTL_IDX(SIOCSIWFRAG)]	= (iw_handler) cfg80211_wext_siwfrag,
-	[IW_IOCTL_IDX(SIOCGIWFRAG)]	= (iw_handler) cfg80211_wext_giwfrag,
-	[IW_IOCTL_IDX(SIOCSIWTXPOW)]	= (iw_handler) cfg80211_wext_siwtxpower,
-	[IW_IOCTL_IDX(SIOCGIWTXPOW)]	= (iw_handler) cfg80211_wext_giwtxpower,
-	[IW_IOCTL_IDX(SIOCSIWRETRY)]	= (iw_handler) cfg80211_wext_siwretry,
-	[IW_IOCTL_IDX(SIOCGIWRETRY)]	= (iw_handler) cfg80211_wext_giwretry,
-	[IW_IOCTL_IDX(SIOCSIWENCODE)]	= (iw_handler) cfg80211_wext_siwencode,
-	[IW_IOCTL_IDX(SIOCGIWENCODE)]	= (iw_handler) cfg80211_wext_giwencode,
-	[IW_IOCTL_IDX(SIOCSIWPOWER)]	= (iw_handler) cfg80211_wext_siwpower,
-	[IW_IOCTL_IDX(SIOCGIWPOWER)]	= (iw_handler) cfg80211_wext_giwpower,
-	[IW_IOCTL_IDX(SIOCSIWGENIE)]	= (iw_handler) cfg80211_wext_siwgenie,
-	[IW_IOCTL_IDX(SIOCSIWAUTH)]	= (iw_handler) cfg80211_wext_siwauth,
-	[IW_IOCTL_IDX(SIOCGIWAUTH)]	= (iw_handler) cfg80211_wext_giwauth,
-	[IW_IOCTL_IDX(SIOCSIWENCODEEXT)]= (iw_handler) cfg80211_wext_siwencodeext,
-	[IW_IOCTL_IDX(SIOCSIWPMKSA)]	= (iw_handler) cfg80211_wext_siwpmksa,
+	[IW_IOCTL_IDX(SIOCGIWNAME)]	= __cfg80211_wext_giwname,
+	[IW_IOCTL_IDX(SIOCSIWFREQ)]	= __cfg80211_wext_siwfreq,
+	[IW_IOCTL_IDX(SIOCGIWFREQ)]	= __cfg80211_wext_giwfreq,
+	[IW_IOCTL_IDX(SIOCSIWMODE)]	= __cfg80211_wext_siwmode,
+	[IW_IOCTL_IDX(SIOCGIWMODE)]	= __cfg80211_wext_giwmode,
+	[IW_IOCTL_IDX(SIOCGIWRANGE)]	= __cfg80211_wext_giwrange,
+	[IW_IOCTL_IDX(SIOCSIWAP)]	= __cfg80211_wext_siwap,
+	[IW_IOCTL_IDX(SIOCGIWAP)]	= __cfg80211_wext_giwap,
+	[IW_IOCTL_IDX(SIOCSIWMLME)]	= __cfg80211_wext_siwmlme,
+	[IW_IOCTL_IDX(SIOCSIWSCAN)]	= cfg80211_wext_siwscan,
+	[IW_IOCTL_IDX(SIOCGIWSCAN)]	= __cfg80211_wext_giwscan,
+	[IW_IOCTL_IDX(SIOCSIWESSID)]	= __cfg80211_wext_siwessid,
+	[IW_IOCTL_IDX(SIOCGIWESSID)]	= __cfg80211_wext_giwessid,
+	[IW_IOCTL_IDX(SIOCSIWRATE)]	= __cfg80211_wext_siwrate,
+	[IW_IOCTL_IDX(SIOCGIWRATE)]	= __cfg80211_wext_giwrate,
+	[IW_IOCTL_IDX(SIOCSIWRTS)]	= __cfg80211_wext_siwrts,
+	[IW_IOCTL_IDX(SIOCGIWRTS)]	= __cfg80211_wext_giwrts,
+	[IW_IOCTL_IDX(SIOCSIWFRAG)]	= __cfg80211_wext_siwfrag,
+	[IW_IOCTL_IDX(SIOCGIWFRAG)]	= __cfg80211_wext_giwfrag,
+	[IW_IOCTL_IDX(SIOCSIWTXPOW)]	= cfg80211_wext_siwtxpower,
+	[IW_IOCTL_IDX(SIOCGIWTXPOW)]	= cfg80211_wext_giwtxpower,
+	[IW_IOCTL_IDX(SIOCSIWRETRY)]	= __cfg80211_wext_siwretry,
+	[IW_IOCTL_IDX(SIOCGIWRETRY)]	= __cfg80211_wext_giwretry,
+	[IW_IOCTL_IDX(SIOCSIWENCODE)]	= __cfg80211_wext_siwencode,
+	[IW_IOCTL_IDX(SIOCGIWENCODE)]	= __cfg80211_wext_giwencode,
+	[IW_IOCTL_IDX(SIOCSIWPOWER)]	= __cfg80211_wext_siwpower,
+	[IW_IOCTL_IDX(SIOCGIWPOWER)]	= __cfg80211_wext_giwpower,
+	[IW_IOCTL_IDX(SIOCSIWGENIE)]	= __cfg80211_wext_siwgenie,
+	[IW_IOCTL_IDX(SIOCSIWAUTH)]	= __cfg80211_wext_siwauth,
+	[IW_IOCTL_IDX(SIOCGIWAUTH)]	= __cfg80211_wext_giwauth,
+	[IW_IOCTL_IDX(SIOCSIWENCODEEXT)]= __cfg80211_wext_siwencodeext,
+	[IW_IOCTL_IDX(SIOCSIWPMKSA)]	= __cfg80211_wext_siwpmksa,
 };
 
 const struct iw_handler_def cfg80211_wext_handler = {