@@ -88,6 +88,15 @@ static void _batadv_update_route(struct batadv_priv *bat_priv,
neigh_node = NULL;
spin_lock_bh(&orig_node->neigh_list_lock);
+ /* curr_router used earlier may not be the current orig_ifinfo->router
+ * anymore because it was dereferenced outside of the neigh_list_lock
+ * protected region. After the new best neighbor has replace the current
+ * best neighbor the reference counter needs to decrease. Consequently,
+ * the code needs to ensure the curr_router variable contains a pointer
+ * to the replaced best neighbor.
+ */
+ curr_router = rcu_dereference_protected(orig_ifinfo->router, true);
+
rcu_assign_pointer(orig_ifinfo->router, neigh_node);
spin_unlock_bh(&orig_node->neigh_list_lock);
batadv_orig_ifinfo_free_ref(orig_ifinfo);
This is a note to let you know that I have just added a patch titled batman-adv: Reduce refcnt of removed router when updating route to the linux-3.19.y-queue branch of the 3.19.y-ckt extended stable tree which can be found at: https://git.launchpad.net/~canonical-kernel/linux/+git/linux-stable-ckt/log/?h=linux-3.19.y-queue This patch is scheduled to be released in version 3.19.8-ckt21. If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.19.y-ckt tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Kamal ---8<------------------------------------------------------------ From bcc00a38eabc53b67322c98024975275c1dc2ea7 Mon Sep 17 00:00:00 2001 From: Sven Eckelmann <sven@narfation.org> Date: Sun, 20 Mar 2016 12:27:53 +0100 Subject: batman-adv: Reduce refcnt of removed router when updating route commit d1a65f1741bfd9c69f9e4e2ad447a89b6810427d upstream. _batadv_update_route rcu_derefences orig_ifinfo->router outside of a spinlock protected region to print some information messages to the debug log. But this pointer is not checked again when the new pointer is assigned in the spinlock protected region. Thus is can happen that the value of orig_ifinfo->router changed in the meantime and thus the reference counter of the wrong router gets reduced after the spinlock protected region. Just rcu_dereferencing the value of orig_ifinfo->router inside the spinlock protected region (which also set the new pointer) is enough to get the correct old router object. Fixes: e1a5382f978b ("batman-adv: Make orig_node->router an rcu protected pointer") Signed-off-by: Sven Eckelmann <sven@narfation.org> Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch> Signed-off-by: Antonio Quartulli <a@unstable.cc> Signed-off-by: Kamal Mostafa <kamal@canonical.com> --- net/batman-adv/routing.c | 9 +++++++++ 1 file changed, 9 insertions(+) -- 2.7.4