nl80211: validate key indexes for cfg80211_registered_device

syzbot discovered a bug in which an OOB access was being made because
an unsuitable key_idx value was wrongly considered to be acceptable
while deleting a key in nl80211_del_key().

Since we don't know the cipher at the time of deletion, if
cfg80211_validate_key_settings() were to be called directly in
nl80211_del_key(), even valid keys would be wrongly determined invalid,
and deletion wouldn't occur correctly.
For this reason, a new function - cfg80211_valid_key_idx(), has been
created, to determine if the key_idx value provided is valid or not.
cfg80211_valid_key_idx() is directly called in 2 places -
nl80211_del_key(), and cfg80211_validate_key_settings().

Reported-by: syzbot+49d4cab497c2142ee170@syzkaller.appspotmail.com
Tested-by: syzbot+49d4cab497c2142ee170@syzkaller.appspotmail.com
Suggested-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Anant Thazhemadam <anant.thazhemadam@gmail.com>
Link: https://lore.kernel.org/r/20201204215825.129879-1-anant.thazhemadam@gmail.com
Cc: stable@vger.kernel.org
[also disallow IGTK key IDs if no IGTK cipher is supported]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/wireless/core.h

@@ -433,6 +433,8 @@ void cfg80211_sme_abandon_assoc(struct wireless_dev *wdev);
 
 /* internal helpers */
 bool cfg80211_supported_cipher_suite(struct wiphy *wiphy, u32 cipher);
+bool cfg80211_valid_key_idx(struct cfg80211_registered_device *rdev,
+			    int key_idx, bool pairwise);
 int cfg80211_validate_key_settings(struct cfg80211_registered_device *rdev,
 				   struct key_params *params, int key_idx,
 				   bool pairwise, const u8 *mac_addr);

net/wireless/nl80211.c

@@ -4239,9 +4239,6 @@ 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]);
 
@@ -4257,6 +4254,10 @@ static int nl80211_del_key(struct sk_buff *skb, struct genl_info *info)
 	    key.type != NL80211_KEYTYPE_GROUP)
 		return -EINVAL;
 
+	if (!cfg80211_valid_key_idx(rdev, key.idx,
+				    key.type == NL80211_KEYTYPE_PAIRWISE))
+		return -EINVAL;
+
 	if (!rdev->ops->del_key)
 		return -EOPNOTSUPP;
 

net/wireless/util.c

@@ -272,18 +272,53 @@ bool cfg80211_supported_cipher_suite(struct wiphy *wiphy, u32 cipher)
 	return false;
 }
 
-int cfg80211_validate_key_settings(struct cfg80211_registered_device *rdev,
-				   struct key_params *params, int key_idx,
-				   bool pairwise, const u8 *mac_addr)
+static bool
+cfg80211_igtk_cipher_supported(struct cfg80211_registered_device *rdev)
 {
-	int max_key_idx = 5;
+	struct wiphy *wiphy = &rdev->wiphy;
+	int i;
+
+	for (i = 0; i < wiphy->n_cipher_suites; i++) {
+		switch (wiphy->cipher_suites[i]) {
+		case WLAN_CIPHER_SUITE_AES_CMAC:
+		case WLAN_CIPHER_SUITE_BIP_CMAC_256:
+		case WLAN_CIPHER_SUITE_BIP_GMAC_128:
+		case WLAN_CIPHER_SUITE_BIP_GMAC_256:
+			return true;
+		}
+	}
+
+	return false;
+}
 
-	if (wiphy_ext_feature_isset(&rdev->wiphy,
-				    NL80211_EXT_FEATURE_BEACON_PROTECTION) ||
-	    wiphy_ext_feature_isset(&rdev->wiphy,
-				    NL80211_EXT_FEATURE_BEACON_PROTECTION_CLIENT))
+bool cfg80211_valid_key_idx(struct cfg80211_registered_device *rdev,
+			    int key_idx, bool pairwise)
+{
+	int max_key_idx;
+
+	if (pairwise)
+		max_key_idx = 3;
+	else if (wiphy_ext_feature_isset(&rdev->wiphy,
+					 NL80211_EXT_FEATURE_BEACON_PROTECTION) ||
+		 wiphy_ext_feature_isset(&rdev->wiphy,
+					 NL80211_EXT_FEATURE_BEACON_PROTECTION_CLIENT))
 		max_key_idx = 7;
+	else if (cfg80211_igtk_cipher_supported(rdev))
+		max_key_idx = 5;
+	else
+		max_key_idx = 3;
+
 	if (key_idx < 0 || key_idx > max_key_idx)
+		return false;
+
+	return true;
+}
+
+int cfg80211_validate_key_settings(struct cfg80211_registered_device *rdev,
+				   struct key_params *params, int key_idx,
+				   bool pairwise, const u8 *mac_addr)
+{
+	if (!cfg80211_valid_key_idx(rdev, key_idx, pairwise))
 		return -EINVAL;
 
 	if (!pairwise && mac_addr && !(rdev->wiphy.flags & WIPHY_FLAG_IBSS_RSN))