[PATCH 3.16 253/305] batman-adv: Fix use-after-free/double-free of tt_req_node

Ben Hutchings
2016-08-14T11:37:12Z

From: Sven Eckelmann <sven@narfation.org>

commit 9c4604a298e0a9807eaf2cd912d1ebf24d98fbeb upstream.

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: a73105b8d4c7 ("batman-adv: improved client announcement mechanism")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Tested-by: Martin Weinelt <martin@darmstadt.freifunk.net>
Tested-by: Amadeus Alfa <amadeus@chemnitz.freifunk.net>
Signed-off-by: Marek Lindner <mareklindner@neomailbox.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.16:
- Adjust context
- Use list_empty() instead of hlist_unhashed()]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
net/batman-adv/translation-table.c | 43 ++++++++++++++++++++++++++++++++------
net/batman-adv/types.h | 2 ++
2 files changed, 39 insertions(+), 6 deletions(-)

--- a/net/batman-adv/translation-table.c
+++ b/net/batman-adv/translation-table.c
@@ -2165,6 +2165,29 @@ static uint32_t batadv_tt_local_crc(stru
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, *safe;
@@ -2173,7 +2196,7 @@ static void batadv_tt_req_list_free(stru

list_for_each_entry_safe(node, safe, &bat_priv->tt.req_list, list) {
list_del(&node->list);
- kfree(node);
+ batadv_tt_req_node_put(node);
}

spin_unlock_bh(&bat_priv->tt.req_list_lock);
@@ -2209,7 +2232,7 @@ static void batadv_tt_req_purge(struct b
if (batadv_has_timed_out(node->issued_at,
BATADV_TT_REQUEST_TIMEOUT)) {
list_del(&node->list);
- kfree(node);
+ batadv_tt_req_node_put(node);
}
}
spin_unlock_bh(&bat_priv->tt.req_list_lock);
@@ -2236,9 +2259,11 @@ batadv_new_tt_req_node(struct batadv_pri
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);
list_add(&tt_req_node->list, &bat_priv->tt.req_list);
unlock:
spin_unlock_bh(&bat_priv->tt.req_list_lock);
@@ -2488,12 +2513,19 @@ static int batadv_send_tt_request(struct
out:
if (primary_if)
batadv_hardif_free_ref(primary_if);
+
if (ret && tt_req_node) {
spin_lock_bh(&bat_priv->tt.req_list_lock);
- list_del(&tt_req_node->list);
+ if (!list_empty(&tt_req_node->list)) {
+ list_del(&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;
}
@@ -2929,7 +2961,7 @@ static void batadv_handle_tt_response(st
if (!batadv_compare_eth(node->addr, resp_src))
continue;
list_del(&node->list);
- kfree(node);
+ batadv_tt_req_node_put(node);
}

spin_unlock_bh(&bat_priv->tt.req_list_lock);
--- a/net/batman-adv/types.h
+++ b/net/batman-adv/types.h
@@ -988,11 +988,13 @@ 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 {
uint8_t addr[ETH_ALEN];
unsigned long issued_at;
+ struct kref refcount;
struct list_head list;
};