From: Sven Eckelmann <sven@narfation.org>
Date: Thu, 3 Oct 2019 17:02:01 +0200
Subject: batman-adv: Avoid free/alloc race when handling OGM buffer

Each slave interface of an B.A.T.M.A.N. IV virtual interface has an OGM
packet buffer which is initialized using data from the RTNL lock protected
netdevice notifier and other rtnetlink related hooks. It is sent regularly
via various slave interfaces of the batadv virtual interface and in this
process also modified (realloced) to integrate additional state information
via TVLV containers.

It must be avoided that the worker item is executed without a common lock
with the netdevice notifier/rtnetlink helpers. Otherwise it can either
happen that half modified/freed data is sent out or functions modifying the
OGM buffer try to access already freed memory regions.

Reported-by: syzbot+0cc629f19ccb8534935b@syzkaller.appspotmail.com
Fixes: ea6f8d42a595 ("batman-adv: move /proc interface handling to /sys")
Signed-off-by: Sven Eckelmann <sven@narfation.org>

Origin: upstream, https://git.open-mesh.org/batman-adv.git/commit/9b8ceef26c697d0c8319748428944c3339a498dc

diff --git a/net/batman-adv/bat_iv_ogm.c b/net/batman-adv/bat_iv_ogm.c
index d78938e3e0085d9cff138b805148a0e77de3f654..e20c3813182c422a52f58178f05010869c5ebe66 100644
--- a/net/batman-adv/bat_iv_ogm.c
+++ b/net/batman-adv/bat_iv_ogm.c
@@ -29,6 +29,7 @@
 #include <linux/random.h>
 #include <linux/rculist.h>
 #include <linux/rcupdate.h>
+#include <linux/rtnetlink.h>
 #include <linux/seq_file.h>
 #include <linux/skbuff.h>
 #include <linux/slab.h>
@@ -193,6 +194,8 @@ static int batadv_iv_ogm_iface_enable(struct batadv_hard_iface *hard_iface)
 	unsigned char *ogm_buff;
 	u32 random_seqno;
 
+	ASSERT_RTNL();
+
 	/* randomize initial seqno to avoid collision */
 	get_random_bytes(&random_seqno, sizeof(random_seqno));
 	atomic_set(&hard_iface->bat_iv.ogm_seqno, random_seqno);
@@ -217,6 +220,8 @@ static int batadv_iv_ogm_iface_enable(struct batadv_hard_iface *hard_iface)
 
 static void batadv_iv_ogm_iface_disable(struct batadv_hard_iface *hard_iface)
 {
+	ASSERT_RTNL();
+
 	kfree(hard_iface->bat_iv.ogm_buff);
 	hard_iface->bat_iv.ogm_buff = NULL;
 }
@@ -226,6 +231,8 @@ static void batadv_iv_ogm_iface_update_mac(struct batadv_hard_iface *hard_iface)
 	struct batadv_ogm_packet *batadv_ogm_packet;
 	unsigned char *ogm_buff = hard_iface->bat_iv.ogm_buff;
 
+	ASSERT_RTNL();
+
 	batadv_ogm_packet = (struct batadv_ogm_packet *)ogm_buff;
 	ether_addr_copy(batadv_ogm_packet->orig,
 			hard_iface->net_dev->dev_addr);
@@ -239,6 +246,8 @@ batadv_iv_ogm_primary_iface_set(struct batadv_hard_iface *hard_iface)
 	struct batadv_ogm_packet *batadv_ogm_packet;
 	unsigned char *ogm_buff = hard_iface->bat_iv.ogm_buff;
 
+	ASSERT_RTNL();
+
 	batadv_ogm_packet = (struct batadv_ogm_packet *)ogm_buff;
 	batadv_ogm_packet->ttl = BATADV_TTL;
 }
@@ -753,6 +762,8 @@ static void batadv_iv_ogm_schedule(struct batadv_hard_iface *hard_iface)
 	u16 tvlv_len = 0;
 	unsigned long send_time;
 
+	ASSERT_RTNL();
+
 	if (hard_iface->if_status == BATADV_IF_NOT_IN_USE ||
 	    hard_iface->if_status == BATADV_IF_TO_BE_REMOVED)
 		return;
@@ -1643,16 +1654,12 @@ static void batadv_iv_ogm_process(const struct sk_buff *skb, int ogm_offset,
 	batadv_orig_node_put(orig_node);
 }
 
-static void batadv_iv_send_outstanding_bat_ogm_packet(struct work_struct *work)
+static void
+batadv_iv_send_outstanding_forw_packet(struct batadv_forw_packet *forw_packet)
 {
-	struct delayed_work *delayed_work;
-	struct batadv_forw_packet *forw_packet;
 	struct batadv_priv *bat_priv;
 	bool dropped = false;
 
-	delayed_work = to_delayed_work(work);
-	forw_packet = container_of(delayed_work, struct batadv_forw_packet,
-				   delayed_work);
 	bat_priv = netdev_priv(forw_packet->if_incoming->soft_iface);
 
 	if (atomic_read(&bat_priv->mesh_state) == BATADV_MESH_DEACTIVATING) {
@@ -1681,6 +1688,20 @@ static void batadv_iv_send_outstanding_bat_ogm_packet(struct work_struct *work)
 		batadv_forw_packet_free(forw_packet, dropped);
 }
 
+static void batadv_iv_send_outstanding_bat_ogm_packet(struct work_struct *work)
+{
+	struct delayed_work *delayed_work;
+	struct batadv_forw_packet *forw_packet;
+
+	delayed_work = to_delayed_work(work);
+	forw_packet = container_of(delayed_work, struct batadv_forw_packet,
+				   delayed_work);
+
+	rtnl_lock();
+	batadv_iv_send_outstanding_forw_packet(forw_packet);
+	rtnl_unlock();
+}
+
 static int batadv_iv_ogm_receive(struct sk_buff *skb,
 				 struct batadv_hard_iface *if_incoming)
 {
diff --git a/net/batman-adv/types.h b/net/batman-adv/types.h
index f298e9a04986faf40db04ece14180b7f43b5a7b7..f3084b005ed641d8ab8910df542762bc7dff450a 100644
--- a/net/batman-adv/types.h
+++ b/net/batman-adv/types.h
@@ -71,10 +71,10 @@ enum batadv_dhcp_recipient {
  * struct batadv_hard_iface_bat_iv - per hard-interface B.A.T.M.A.N. IV data
  */
 struct batadv_hard_iface_bat_iv {
-	/** @ogm_buff: buffer holding the OGM packet */
+	/** @ogm_buff: buffer holding the OGM packet. rtnl protected */
 	unsigned char *ogm_buff;
 
-	/** @ogm_buff_len: length of the OGM packet buffer */
+	/** @ogm_buff_len: length of the OGM packet buffer. rtnl protected */
 	int ogm_buff_len;
 
 	/** @ogm_seqno: OGM sequence number - used to identify each OGM */