release/5.2.22/nl80211-validate-beacon-head.patch

From 71a265419348c2ba9a8b7b24e16aded3dd4fd954 Mon Sep 17 00:00:00 2001
From: Johannes Berg <johannes.berg@intel.com>
Date: Fri, 20 Sep 2019 21:54:17 +0200
Subject: [PATCH] nl80211: validate beacon head

commit f88eb7c0d002a67ef31aeb7850b42ff69abc46dc upstream.

We currently don't validate the beacon head, i.e. the header,
fixed part and elements that are to go in front of the TIM
element. This means that the variable elements there can be
malformed, e.g. have a length exceeding the buffer size, but
most downstream code from this assumes that this has already
been checked.

Add the necessary checks to the netlink policy.

Cc: stable@vger.kernel.org
Fixes: ed1b6cc7f80f ("cfg80211/nl80211: add beacon settings")
Link: https://lore.kernel.org/r/1569009255-I7ac7fbe9436e9d8733439eab8acbbd35e55c74ef@changeid
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

diff --git a/net/wireless/nl80211.c b/net/wireless/nl80211.c
index b28aaddbe08e..73891b7c2f8b 100644
--- a/net/wireless/nl80211.c
+++ b/net/wireless/nl80211.c
@@ -201,6 +201,38 @@ cfg80211_get_dev_from_info(struct net *netns, struct genl_info *info)
 	return __cfg80211_rdev_from_attrs(netns, info->attrs);
 }
 
+static int validate_beacon_head(const struct nlattr *attr,
+				struct netlink_ext_ack *extack)
+{
+	const u8 *data = nla_data(attr);
+	unsigned int len = nla_len(attr);
+	const struct element *elem;
+	const struct ieee80211_mgmt *mgmt = (void *)data;
+	unsigned int fixedlen = offsetof(struct ieee80211_mgmt,
+					 u.beacon.variable);
+
+	if (len < fixedlen)
+		goto err;
+
+	if (ieee80211_hdrlen(mgmt->frame_control) !=
+	    offsetof(struct ieee80211_mgmt, u.beacon))
+		goto err;
+
+	data += fixedlen;
+	len -= fixedlen;
+
+	for_each_element(elem, data, len) {
+		/* nothing */
+	}
+
+	if (for_each_element_completed(elem, data, len))
+		return 0;
+
+err:
+	NL_SET_ERR_MSG_ATTR(extack, attr, "malformed beacon head");
+	return -EINVAL;
+}
+
 static int validate_ie_attr(const struct nlattr *attr,
 			    struct netlink_ext_ack *extack)
 {
@@ -322,8 +354,9 @@ const struct nla_policy nl80211_policy[NUM_NL80211_ATTR] = {
 
 	[NL80211_ATTR_BEACON_INTERVAL] = { .type = NLA_U32 },
 	[NL80211_ATTR_DTIM_PERIOD] = { .type = NLA_U32 },
-	[NL80211_ATTR_BEACON_HEAD] = { .type = NLA_BINARY,
-				       .len = IEEE80211_MAX_DATA_LEN },
+	[NL80211_ATTR_BEACON_HEAD] =
+		NLA_POLICY_VALIDATE_FN(NLA_BINARY, validate_beacon_head,
+				       IEEE80211_MAX_DATA_LEN),
 	[NL80211_ATTR_BEACON_TAIL] =
 		NLA_POLICY_VALIDATE_FN(NLA_BINARY, validate_ie_attr,
 				       IEEE80211_MAX_DATA_LEN),
-- 
2.7.4