cfg80211: wext: avoid copying malformed SSIDs

commit 4ac2813cc867ae563a1ba5a9414bfb554e5796fa upstream.

Ensure the SSID element is bounds-checked prior to invoking memcpy()
with its length field, when copying to userspace.

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/20191004095132.15777-2-will@kernel.org
[adjust commit log a bit]
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/net/wireless/wext-sme.c b/net/wireless/wext-sme.c
index c7e5c8eb4f24708a27d90ae298a85c825ee81e38..e95b5e949406dd5894f93ca87d0a6df2ad9d0c6d 100644 (file)
--- a/net/wireless/wext-sme.c
+++ b/net/wireless/wext-sme.c
@@ -225,6 +225,7 @@ int cfg80211_mgd_wext_giwessid(struct net_device *dev,
                               struct iw_point *data, char *ssid)
 {
        struct wireless_dev *wdev = dev->ieee80211_ptr;
+       int ret = 0;
 
        /* call only for station! */
        if (WARN_ON(wdev->iftype != NL80211_IFTYPE_STATION))
@@ -242,7 +243,10 @@ int cfg80211_mgd_wext_giwessid(struct net_device *dev,
                if (ie) {
                        data->flags = 1;
                        data->length = ie[1];
-                       memcpy(ssid, ie + 2, data->length);
+                       if (data->length > IW_ESSID_MAX_SIZE)
+                               ret = -EINVAL;
+                       else
+                               memcpy(ssid, ie + 2, data->length);
                }
                rcu_read_unlock();
        } else if (wdev->wext.connect.ssid && wdev->wext.connect.ssid_len) {
@@ -252,7 +256,7 @@ int cfg80211_mgd_wext_giwessid(struct net_device *dev,
        }
        wdev_unlock(wdev);
 
-       return 0;
+       return ret;
 }
 
 int cfg80211_mgd_wext_siwap(struct net_device *dev,