wifi: rtw89: mcc: prevent shift wrapping in rtw89_core_mlsr_switch()

The "link_id" value comes from the user via debugfs.  If it's larger
than BITS_PER_LONG then that would result in shift wrapping and
potentially an out of bounds access later.  In fact, we can limit it
to IEEE80211_MLD_MAX_NUM_LINKS (15).

Fortunately, only root can write to debugfs files so the security
impact is minimal.

Fixes: 9dd85e7 ("wifi: rtw89: debug: add mlo_mode dbgfs")
Signed-off-by: Dan Carpenter <[email protected]>
Reviewed-by: Zong-Zhe Yang <[email protected]>
Signed-off-by: Ping-Ke Shih <[email protected]>
Link: https://patch.msgid.link/[email protected]

Author: Dan Carpenter

drivers/net/wireless/realtek/rtw89/core.c

@@ -5239,7 +5239,8 @@ int rtw89_core_mlsr_switch(struct rtw89_dev *rtwdev, struct rtw89_vif *rtwvif,
 	if (unlikely(!ieee80211_vif_is_mld(vif)))
 		return -EOPNOTSUPP;
 
-	if (unlikely(!(usable_links & BIT(link_id)))) {
+	if (unlikely(link_id >= IEEE80211_MLD_MAX_NUM_LINKS ||
+		     !(usable_links & BIT(link_id)))) {
 		rtw89_warn(rtwdev, "%s: link id %u is not usable\n", __func__,
 			   link_id);
 		return -ENOLINK;