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Commit 9c4604a2 authored by Sven Eckelmann's avatar Sven Eckelmann Committed by David S. Miller
Browse files

batman-adv: Fix use-after-free/double-free of tt_req_node 



The tt_req_node is added and removed from a list inside a spinlock. But the
locking is sometimes removed even when the object is still referenced and
will be used later via this reference. For example batadv_send_tt_request
can create a new tt_req_node (including add to a list) and later
re-acquires the lock to remove it from the list and to free it. But at this
time another context could have already removed this tt_req_node from the
list and freed it.

CPU#0

    batadv_batman_skb_recv from net_device 0
    -> batadv_iv_ogm_receive
      -> batadv_iv_ogm_process
        -> batadv_iv_ogm_process_per_outif
          -> batadv_tvlv_ogm_receive
            -> batadv_tvlv_ogm_receive
              -> batadv_tvlv_containers_process
                -> batadv_tvlv_call_handler
                  -> batadv_tt_tvlv_ogm_handler_v1
                    -> batadv_tt_update_orig
                      -> batadv_send_tt_request
                        -> batadv_tt_req_node_new
                           spin_lock(...)
                           allocates new tt_req_node and adds it to list
                           spin_unlock(...)
                           return tt_req_node

CPU#1

    batadv_batman_skb_recv from net_device 1
    -> batadv_recv_unicast_tvlv
      -> batadv_tvlv_containers_process
        -> batadv_tvlv_call_handler
          -> batadv_tt_tvlv_unicast_handler_v1
            -> batadv_handle_tt_response
               spin_lock(...)
               tt_req_node gets removed from list and is freed
               spin_unlock(...)

CPU#0

                      <- returned to batadv_send_tt_request
                         spin_lock(...)
                         tt_req_node gets removed from list and is freed
                         MEMORY CORRUPTION/SEGFAULT/...
                         spin_unlock(...)

This can only be solved via reference counting to allow multiple contexts
to handle the list manipulation while making sure that only the last
context holding a reference will free the object.

Fixes: a73105b8 ("batman-adv: improved client announcement mechanism")
Signed-off-by: default avatarSven Eckelmann <sven@narfation.org>
Tested-by: default avatarMartin Weinelt <martin@darmstadt.freifunk.net>
Tested-by: default avatarAmadeus Alfa <amadeus@chemnitz.freifunk.net>
Signed-off-by: default avatarMarek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 0b3dd7df

net/batman-adv/translation-table.c

+37 −6
Original line number Diff line number Diff line
@@ -2271,6 +2271,29 @@ static u32 batadv_tt_local_crc(struct batadv_priv *bat_priv, 
	return crc;

}



/**

 * batadv_tt_req_node_release - free tt_req node entry

 * @ref: kref pointer of the tt req_node entry

 */

static void batadv_tt_req_node_release(struct kref *ref)

{

	struct batadv_tt_req_node *tt_req_node;



	tt_req_node = container_of(ref, struct batadv_tt_req_node, refcount);



	kfree(tt_req_node);

}



/**

 * batadv_tt_req_node_put - decrement the tt_req_node refcounter and

 *  possibly release it

 * @tt_req_node: tt_req_node to be free'd

 */

static void batadv_tt_req_node_put(struct batadv_tt_req_node *tt_req_node)

{

	kref_put(&tt_req_node->refcount, batadv_tt_req_node_release);

}



static void batadv_tt_req_list_free(struct batadv_priv *bat_priv)

{

	struct batadv_tt_req_node *node;
@@ -2280,7 +2303,7 @@ static void batadv_tt_req_list_free(struct batadv_priv *bat_priv) 


	hlist_for_each_entry_safe(node, safe, &bat_priv->tt.req_list, list) {

		hlist_del_init(&node->list);

		kfree(node);

		batadv_tt_req_node_put(node);

	}



	spin_unlock_bh(&bat_priv->tt.req_list_lock);
@@ -2317,7 +2340,7 @@ static void batadv_tt_req_purge(struct batadv_priv *bat_priv) 
		if (batadv_has_timed_out(node->issued_at,

					 BATADV_TT_REQUEST_TIMEOUT)) {

			hlist_del_init(&node->list);

			kfree(node);

			batadv_tt_req_node_put(node);

		}

	}

	spin_unlock_bh(&bat_priv->tt.req_list_lock);
@@ -2349,9 +2372,11 @@ batadv_tt_req_node_new(struct batadv_priv *bat_priv, 
	if (!tt_req_node)

		goto unlock;



	kref_init(&tt_req_node->refcount);

	ether_addr_copy(tt_req_node->addr, orig_node->orig);

	tt_req_node->issued_at = jiffies;



	kref_get(&tt_req_node->refcount);

	hlist_add_head(&tt_req_node->list, &bat_priv->tt.req_list);

unlock:

	spin_unlock_bh(&bat_priv->tt.req_list_lock);
@@ -2615,13 +2640,19 @@ static bool batadv_send_tt_request(struct batadv_priv *bat_priv, 
out:

	if (primary_if)

		batadv_hardif_put(primary_if);



	if (ret && tt_req_node) {

		spin_lock_bh(&bat_priv->tt.req_list_lock);

		/* hlist_del_init() verifies tt_req_node still is in the list */

		if (!hlist_unhashed(&tt_req_node->list)) {

			hlist_del_init(&tt_req_node->list);

			batadv_tt_req_node_put(tt_req_node);

		}

		spin_unlock_bh(&bat_priv->tt.req_list_lock);

		kfree(tt_req_node);

	}



	if (tt_req_node)

		batadv_tt_req_node_put(tt_req_node);



	kfree(tvlv_tt_data);

	return ret;

}
@@ -3057,7 +3088,7 @@ static void batadv_handle_tt_response(struct batadv_priv *bat_priv, 
		if (!batadv_compare_eth(node->addr, resp_src))

			continue;

		hlist_del_init(&node->list);

		kfree(node);

		batadv_tt_req_node_put(node);

	}



	spin_unlock_bh(&bat_priv->tt.req_list_lock);

net/batman-adv/types.h

+2 −0
Original line number Diff line number Diff line
@@ -1137,11 +1137,13 @@ struct batadv_tt_change_node { 
 * struct batadv_tt_req_node - data to keep track of the tt requests in flight

 * @addr: mac address address of the originator this request was sent to

 * @issued_at: timestamp used for purging stale tt requests

 * @refcount: number of contexts the object is used by

 * @list: list node for batadv_priv_tt::req_list

 */

struct batadv_tt_req_node {

	u8 addr[ETH_ALEN];

	unsigned long issued_at;

	struct kref refcount;

	struct hlist_node list;

};