[maint,v3] batman-adv: Fix use-after-free/double-free of tt_req_node
Commit Message
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: cea194d90b11 ("batman-adv: improved client announcement mechanism")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Tested-by: Martin Weinelt <martin@darmstadt.freifunk.net>
---
v3:
- add wrapper function batadv_tt_req_node_put for kref_put(....)
v2:
- fixed list->object in commit message
- add example what could have gone wrong in commit message
---
net/batman-adv/translation-table.c | 37 +++++++++++++++++++++++++++++++++----
net/batman-adv/types.h | 2 ++
2 files changed, 35 insertions(+), 4 deletions(-)
Comments
On Saturday, June 04, 2016 08:52:12 Sven Eckelmann wrote:
> 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: cea194d90b11 ("batman-adv: improved client announcement mechanism")
> Signed-off-by: Sven Eckelmann <sven@narfation.org>
> Tested-by: Martin Weinelt <martin@darmstadt.freifunk.net>
> ---
> v3:
> - add wrapper function batadv_tt_req_node_put for kref_put(....)
> v2:
> - fixed list->object in commit message
> - add example what could have gone wrong in commit message
> ---
> net/batman-adv/translation-table.c | 37
> +++++++++++++++++++++++++++++++++----
> net/batman-adv/types.h | 2 ++
> 2 files changed, 35 insertions(+), 4 deletions(-)
Applied in revision c3fef3d.
Thanks,
Marek
@@ -2272,6 +2272,29 @@ 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;
@@ -2281,7 +2304,7 @@ 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);
@@ -2318,7 +2341,7 @@ 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);
@@ -2350,9 +2373,11 @@ 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);
@@ -2619,9 +2644,13 @@ out:
spin_lock_bh(&bat_priv->tt.req_list_lock);
/* hlist_del_init() verifies tt_req_node still is in the 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 +3086,7 @@ 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);
@@ -1129,11 +1129,13 @@ 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;
};