mac80211: mesh: fix call_rcu() usage

When using call_rcu(), the called function may be delayed quite
significantly, and without a matching rcu_barrier() there's no
way to be sure it has finished.
Therefore, global state that could be gone/freed/reused should
never be touched in the callback.

Fix this in mesh by moving the atomic_dec() into the caller;
that's not really a problem since we already unlinked the path
and it will be destroyed anyway.

This fixes a crash Jouni observed when running certain tests in
a certain order, in which the mesh interface was torn down, the
memory reused for a function pointer (work struct) and running
that then crashed since the pointer had been decremented by 1,
resulting in an invalid instruction byte stream.

Cc: stable@vger.kernel.org
Fixes: eb2b9311fd00 ("mac80211: mesh path table implementation")
Reported-by: Jouni Malinen <j@w1.fi>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

diff --git a/net/mac80211/mesh_pathtbl.c b/net/mac80211/mesh_pathtbl.c
index b890e225a8f1b98681c53c764fc5252e5f2d5c8d..b3b44a5dd375c3a4bc391e29de21ae702a62418d 100644 (file)
--- a/net/mac80211/mesh_pathtbl.c
+++ b/net/mac80211/mesh_pathtbl.c
@@ -779,10 +779,8 @@ void mesh_plink_broken(struct sta_info *sta)
 static void mesh_path_node_reclaim(struct rcu_head *rp)
 {
        struct mpath_node *node = container_of(rp, struct mpath_node, rcu);
-       struct ieee80211_sub_if_data *sdata = node->mpath->sdata;
 
        del_timer_sync(&node->mpath->timer);
-       atomic_dec(&sdata->u.mesh.mpaths);
        kfree(node->mpath);
        kfree(node);
 }
@@ -790,8 +788,9 @@ static void mesh_path_node_reclaim(struct rcu_head *rp)
 /* needs to be called with the corresponding hashwlock taken */
 static void __mesh_path_del(struct mesh_table *tbl, struct mpath_node *node)
 {
-       struct mesh_path *mpath;
-       mpath = node->mpath;
+       struct mesh_path *mpath = node->mpath;
+       struct ieee80211_sub_if_data *sdata = node->mpath->sdata;
+
        spin_lock(&mpath->state_lock);
        mpath->flags |= MESH_PATH_RESOLVING;
        if (mpath->is_gate)
@@ -799,6 +798,7 @@ static void __mesh_path_del(struct mesh_table *tbl, struct mpath_node *node)
        hlist_del_rcu(&node->list);
        call_rcu(&node->rcu, mesh_path_node_reclaim);
        spin_unlock(&mpath->state_lock);
+       atomic_dec(&sdata->u.mesh.mpaths);
        atomic_dec(&tbl->entries);
 }