mac80211: fix possible null-pointer de-reference

This patch not only fixes a null-pointer de-reference
that would be triggered by a PLINK_OPEN frame with mis-
matching/incompatible mesh configuration, but also
responds correctly to non-compatible PLINK_OPEN frames
by generating a PLINK_CLOSE with the right reason code.

The original bug was detected by smatch.
( http://repo.or.cz/w/smatch.git )

net/mac80211/mesh_plink.c +574 mesh_rx_plink_frame(168)
error: we previously assumed 'sta' could be null.

Cc: <stable@kernel.org>
Reviewed-and-Tested-by: Steve deRosier <steve@cozybit.com>
Reviewed-and-Tested-by: Javier Cardona <javier@cozybit.com>
Acked-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

1 files changed, 14 insertions, 3 deletions

diff --git a/net/mac80211/mesh_plink.c b/net/mac80211/mesh_plink.c
index ea13a80a476..1c91f0f3c30 100644
--- a/net/mac80211/mesh_plink.c
+++ b/net/mac80211/mesh_plink.c
@@ -412,7 +412,7 @@ void mesh_rx_plink_frame(struct ieee80211_sub_if_data *sdata, struct ieee80211_m
         enum plink_event event;
         enum plink_frame_type ftype;
         size_t baselen;
-        bool deactivated;
+        bool deactivated, matches_local = true;
         u8 ie_len;
         u8 *baseaddr;
         __le16 plid, llid, reason;
@@ -487,6 +487,7 @@ void mesh_rx_plink_frame(struct ieee80211_sub_if_data *sdata, struct ieee80211_m
         /* Now we will figure out the appropriate event... */
         event = PLINK_UNDEFINED;
         if (ftype != PLINK_CLOSE && (!mesh_matches_local(&elems, sdata))) {
+                matches_local = false;
                 switch (ftype) {
                 case PLINK_OPEN:
                         event = OPN_RJCT;
@@ -498,7 +499,15 @@ void mesh_rx_plink_frame(struct ieee80211_sub_if_data *sdata, struct ieee80211_m
                         /* avoid warning */
                         break;
                 }
-                spin_lock_bh(&sta->lock);
+        }
+
+        if (!sta && !matches_local) {
+                rcu_read_unlock();
+                reason = cpu_to_le16(MESH_CAPABILITY_POLICY_VIOLATION);
+                llid = 0;
+                mesh_plink_frame_tx(sdata, PLINK_CLOSE, mgmt->sa, llid,
+                                    plid, reason);
+                return;
         } else if (!sta) {
                 /* ftype == PLINK_OPEN */
                 u32 rates;
@@ -522,7 +531,7 @@ void mesh_rx_plink_frame(struct ieee80211_sub_if_data *sdata, struct ieee80211_m
                 }
                 event = OPN_ACPT;
                 spin_lock_bh(&sta->lock);
-        } else {
+        } else if (matches_local) {
                 spin_lock_bh(&sta->lock);
                 switch (ftype) {
                 case PLINK_OPEN:
@@ -564,6 +573,8 @@ void mesh_rx_plink_frame(struct ieee80211_sub_if_data *sdata, struct ieee80211_m
                         rcu_read_unlock();
                         return;
                 }
+        } else {
+                spin_lock_bh(&sta->lock);
         }
 
         mpl_dbg("Mesh plink (peer, state, llid, plid, event): %pM %s %d %d %d\n",