linux-kernel - [PATCH 3.16 023/136] mac80211: Reject malformed SSID elements

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Message-ID: <lsq.1576543535.569796514@decadent.org.uk>
Date:   Tue, 17 Dec 2019 00:45:57 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Nicolas Waisman" <nico@...mle.com>,
        "Will Deacon" <will@...nel.org>,
        "Johannes Berg" <johannes.berg@...el.com>,
        "Kees Cook" <keescook@...omium.org>
Subject: [PATCH 3.16 023/136] mac80211: Reject malformed SSID elements

3.16.80-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Will Deacon <will@...nel.org>

commit 4152561f5da3fca92af7179dd538ea89e248f9d0 upstream.

Although this shouldn't occur in practice, it's a good idea to bounds
check the length field of the SSID element prior to using it for things
like allocations or memcpy operations.

Cc: Kees Cook <keescook@...omium.org>
Reported-by: Nicolas Waisman <nico@...mle.com>
Signed-off-by: Will Deacon <will@...nel.org>
Link: https://lore.kernel.org/r/20191004095132.15777-1-will@kernel.org
Signed-off-by: Johannes Berg <johannes.berg@...el.com>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 net/mac80211/mlme.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

--- a/net/mac80211/mlme.c
+++ b/net/mac80211/mlme.c
@@ -2046,7 +2046,8 @@ struct sk_buff *ieee80211_ap_probereq_ge
 
 	rcu_read_lock();
 	ssid = ieee80211_bss_get_ie(cbss, WLAN_EID_SSID);
-	if (WARN_ON_ONCE(ssid == NULL))
+	if (WARN_ONCE(!ssid || ssid[1] > IEEE80211_MAX_SSID_LEN,
+		      "invalid SSID element (len=%d)", ssid ? ssid[1] : -1))
 		ssid_len = 0;
 	else
 		ssid_len = ssid[1];
@@ -4195,7 +4196,7 @@ int ieee80211_mgd_assoc(struct ieee80211
 
 	rcu_read_lock();
 	ssidie = ieee80211_bss_get_ie(req->bss, WLAN_EID_SSID);
-	if (!ssidie) {
+	if (!ssidie || ssidie[1] > sizeof(assoc_data->ssid)) {
 		rcu_read_unlock();
 		kfree(assoc_data);
 		return -EINVAL;