caif: Bugfix list_del_rcu race in cfmuxl_ctrlcmd.

Always use cfmuxl_remove_uplayer when removing a up-layer.
cfmuxl_ctrlcmd() can be called independently and in parallel with
cfmuxl_remove_uplayer(). The race between them could cause list_del_rcu
to be called on a node which has been already taken out from the list.
That lead to a (rare) crash on accessing poisoned node->prev inside
list_del_rcu.

This fix ensures that deletion are done holding the same lock.

Reported-by: Dmitry Tarnyagin <dmitry.tarnyagin@stericsson.com>
Signed-off-by: Sjur Brændeland <sjur.brandeland@stericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 3 insertions, 9 deletions

diff --git a/net/caif/cfmuxl.c b/net/caif/cfmuxl.c
index b36f24a4c8e7..94b08612a4d8 100644
--- a/net/caif/cfmuxl.c
+++ b/net/caif/cfmuxl.c
@@ -248,7 +248,6 @@ static void cfmuxl_ctrlcmd(struct cflayer *layr, enum caif_ctrlcmd ctrl,
 {
         struct cfmuxl *muxl = container_obj(layr);
         struct cflayer *layer;
-        int idx;
 
         rcu_read_lock();
         list_for_each_entry_rcu(layer, &muxl->srvl_list, node) {
@@ -257,14 +256,9 @@ static void cfmuxl_ctrlcmd(struct cflayer *layr, enum caif_ctrlcmd ctrl,
 
                         if ((ctrl == _CAIF_CTRLCMD_PHYIF_DOWN_IND ||
                                 ctrl == CAIF_CTRLCMD_REMOTE_SHUTDOWN_IND) &&
-                                        layer->id != 0) {
-
-                                idx = layer->id % UP_CACHE_SIZE;
-                                spin_lock_bh(&muxl->receive_lock);
-                                RCU_INIT_POINTER(muxl->up_cache[idx], NULL);
-                                list_del_rcu(&layer->node);
-                                spin_unlock_bh(&muxl->receive_lock);
-                        }
+                                        layer->id != 0)
+                                cfmuxl_remove_uplayer(layr, layer->id);
+
                         /* NOTE: ctrlcmd is not allowed to block */
                         layer->ctrlcmd(layer, ctrl, phyid);
                 }