net: wireless: nl80211: fix out-of-bounds access in nl80211_del_key()

In nl80211_parse_key(), key.idx is first initialized as -1.
If this value of key.idx remains unmodified and gets returned, and
nl80211_key_allowed() also returns 0, then rdev_del_key() gets called
with key.idx = -1.
This causes an out-of-bounds array access.

Handle this issue by checking if the value of key.idx after
nl80211_parse_key() is called and return -EINVAL if key.idx < 0.

Cc: stable@vger.kernel.org
Reported-by: syzbot+b1bb342d1d097516cbda@syzkaller.appspotmail.com
Tested-by: syzbot+b1bb342d1d097516cbda@syzkaller.appspotmail.com
Signed-off-by: Anant Thazhemadam <anant.thazhemadam@gmail.com>
Link: https://lore.kernel.org/r/20201007035401.9522-1-anant.thazhemadam@gmail.comSigned-off-by: Johannes Berg <johannes.berg@intel.com>

net/wireless/nl80211.c

@@ -4172,6 +4172,9 @@ static int nl80211_del_key(struct sk_buff *skb, struct genl_info *info)
 	if (err)
 		return err;
 
+	if (key.idx < 0)
+		return -EINVAL;
+
 	if (info->attrs[NL80211_ATTR_MAC])
 		mac_addr = nla_data(info->attrs[NL80211_ATTR_MAC]);