[PATCH 3.16 276/306] tipc: check minimum bearer MTU

Ben Hutchings
2017-02-15T23:13:18Z

From: Michal Kubeček <mkubecek@suse.cz>

commit 3de81b758853f0b29c61e246679d20b513c4cfec upstream.

Qian Zhang (张谦) reported a potential socket buffer overflow in
tipc_msg_build() which is also known as CVE-2016-8632: due to
insufficient checks, a buffer overflow can occur if MTU is too short for
even tipc headers. As anyone can set device MTU in a user/net namespace,
this issue can be abused by a regular user.

As agreed in the discussion on Ben Hutchings' original patch, we should
check the MTU at the moment a bearer is attached rather than for each
processed packet. We also need to repeat the check when bearer MTU is
adjusted to new device MTU. UDP case also needs a check to avoid
overflow when calculating bearer MTU.

Fixes: b97bf3fd8f6a ("[TIPC] Initial merge")
Signed-off-by: Michal Kubecek <mkubecek@suse.cz>
Reported-by: Qian Zhang (张谦) <zhangqian-c@360.cn>
Acked-by: Ying Xue <ying.xue@windriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 3.16:
- Adjust context
- Duplicate macro definitions in bearer.h to avoid mutual inclusion
- NETDEV_DOWN and NETDEV_CHANGEMTU cases in net notifier were combined
- Drop changes in udp_media.c]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/net/tipc/bearer.c
+++ b/net/tipc/bearer.c
@@ -420,6 +420,10 @@ int tipc_enable_l2_media(struct tipc_bea
dev = dev_get_by_name(&init_net, driver_name);
if (!dev)
return -ENODEV;
+ if (tipc_mtu_bad(dev, 0)) {
+ dev_put(dev);
+ return -EINVAL;
+ }

/* Associate TIPC bearer with L2 bearer */
rcu_assign_pointer(b->media_ptr, dev);
@@ -564,14 +568,19 @@ static int tipc_l2_device_event(struct n
if (!b_ptr)
return NOTIFY_DONE;

- b_ptr->mtu = dev->mtu;
-
switch (evt) {
case NETDEV_CHANGE:
if (netif_carrier_ok(dev))
break;
case NETDEV_DOWN:
+ tipc_reset_bearer(b_ptr);
+ break;
case NETDEV_CHANGEMTU:
+ if (tipc_mtu_bad(dev, 0)) {
+ bearer_disable(b_ptr, false);
+ break;
+ }
+ b_ptr->mtu = dev->mtu;
tipc_reset_bearer(b_ptr);
break;
case NETDEV_CHANGEADDR:
--- a/net/tipc/bearer.h
+++ b/net/tipc/bearer.h
@@ -50,6 +50,13 @@
#define TIPC_MEDIA_ADDR_SIZE 32
#define TIPC_MEDIA_TYPE_OFFSET 3

+/* Message header sizes from msg.h - duplicated to avoid mutual inclusion */
+#define INT_H_SIZE 40
+#define MAX_H_SIZE 60
+
+/* minimum bearer MTU */
+#define TIPC_MIN_BEARER_MTU (MAX_H_SIZE + INT_H_SIZE)
+
/*
* Identifiers of supported TIPC media types
*/
@@ -196,4 +203,13 @@ void tipc_bearer_stop(void);
void tipc_bearer_send(u32 bearer_id, struct sk_buff *buf,
struct tipc_media_addr *dest);

+/* check if device MTU is too low for tipc headers */
+static inline bool tipc_mtu_bad(struct net_device *dev, unsigned int reserve)
+{
+ if (dev->mtu >= TIPC_MIN_BEARER_MTU + reserve)
+ return false;
+ netdev_warn(dev, "MTU too low for tipc bearer\n");
+ return true;
+}
+
#endif /* _TIPC_BEARER_H */