[PATCH] net: wireless: validate key indexes for cfg80211_registered_device

[Anant Thazhemadam]

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@xxxxxxxxxxxxxxxxxxxxxxxxx
Tested-by: syzbot+49d4cab497c2142ee170@xxxxxxxxxxxxxxxxxxxxxxxxx
Suggested-by: Johannes Berg <johannes@xxxxxxxxxxxxxxxx>
Signed-off-by: Anant Thazhemadam <anant.thazhemadam@xxxxxxxxx>
---
For the bug that was getting triggered, pairwise was true, and 
the NL80211_EXT_FEATURE_BEACON_PROTECTION feature was set too.
The control logic for cfg80211_validate_key_settings() has been
designed keeping this also in mind.

 net/wireless/core.h    |  2 ++
 net/wireless/nl80211.c |  7 ++++---
 net/wireless/util.c    | 27 ++++++++++++++++++++-------
 3 files changed, 26 insertions(+), 10 deletions(-)

diff --git a/net/wireless/core.h b/net/wireless/core.h
index e3e9686859d4..7df91f940212 100644
--- a/net/wireless/core.h
+++ b/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);
diff --git a/net/wireless/nl80211.c b/net/wireless/nl80211.c
index a77174b99b07..db36158911ae 100644
--- a/net/wireless/nl80211.c
+++ b/net/wireless/nl80211.c
@@ -4260,9 +4260,6 @@ 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]);
 
@@ -4278,6 +4275,10 @@ 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;
 
diff --git a/net/wireless/util.c b/net/wireless/util.c
index f01746894a4e..07b17feb9b1e 100644
--- a/net/wireless/util.c
+++ b/net/wireless/util.c
@@ -272,18 +272,31 @@ 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)
+bool cfg80211_valid_key_idx(struct cfg80211_registered_device *rdev,
+			    int key_idx, bool pairwise)
 {
 	int max_key_idx = 5;
 
-	if (wiphy_ext_feature_isset(&rdev->wiphy,
-				    NL80211_EXT_FEATURE_BEACON_PROTECTION) ||
-	    wiphy_ext_feature_isset(&rdev->wiphy,
-				    NL80211_EXT_FEATURE_BEACON_PROTECTION_CLIENT))
+	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;
+
 	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))
-- 
2.25.1