mac80211: Reject malformed SSID elements

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: <stable@vger.kernel.org>
Cc: Kees Cook <keescook@chromium.org>
Reported-by: Nicolas Waisman <nico@semmle.com>
Signed-off-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20191004095132.15777-1-will@kernel.org
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

1 files changed, 3 insertions, 2 deletions

diff --git a/net/mac80211/mlme.c b/net/mac80211/mlme.c
index 26a2f49208b6..54dd8849d1cc 100644
--- a/net/mac80211/mlme.c
+++ b/net/mac80211/mlme.c
@@ -2633,7 +2633,8 @@ struct sk_buff *ieee80211_ap_probereq_get(struct ieee80211_hw *hw,
 
         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];
@@ -5233,7 +5234,7 @@ int ieee80211_mgd_assoc(struct ieee80211_sub_if_data *sdata,
 
         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;