cfg80211: wext: avoid copying malformed SSIDs

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

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

1 files changed, 6 insertions, 2 deletions

diff --git a/net/wireless/wext-sme.c b/net/wireless/wext-sme.c
index c67d7a82ab13..73fd0eae08ca 100644
--- a/net/wireless/wext-sme.c
+++ b/net/wireless/wext-sme.c
@@ -202,6 +202,7 @@ 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))
@@ -219,7 +220,10 @@ 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) {
@@ -229,7 +233,7 @@ 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,