[PATCH 3.2 097/126] tipc: check minimum bearer MTU

Ben Hutchings
2017-02-15T23:31:19Z

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 3.2:
- Adjust filename, context
- Duplicate macro definitions in bearer.h to avoid mutual inclusion
- NETDEV_CHANGEMTU and NETDEV_CHANGEADDR cases in net notifier were combined
- Drop changes in udp_media.c]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
---
--- a/net/tipc/eth_media.c
+++ b/net/tipc/eth_media.c
@@ -167,6 +167,10 @@ static int enable_bearer(struct tipc_bea
read_unlock(&dev_base_lock);
if (!dev)
return -ENODEV;
+ if (tipc_mtu_bad(dev, 0)) {
+ dev_put(dev);
+ return -EINVAL;
+ }

/* Create Ethernet bearer for device */

@@ -227,8 +231,6 @@ static int recv_notification(struct noti
if (!eb_ptr->bearer)
return NOTIFY_DONE; /* bearer had been disabled */

- eb_ptr->bearer->mtu = dev->mtu;
-
switch (evt) {
case NETDEV_CHANGE:
if (netif_carrier_ok(dev))
@@ -243,6 +245,12 @@ static int recv_notification(struct noti
tipc_block_bearer(eb_ptr->bearer->name);
break;
case NETDEV_CHANGEMTU:
+ if (tipc_mtu_bad(dev, 0)) {
+ tipc_disable_bearer(eb_ptr->bearer->name);
+ break;
+ }
+ eb_ptr->bearer->mtu = dev->mtu;
+ /* fall through */
case NETDEV_CHANGEADDR:
tipc_block_bearer(eb_ptr->bearer->name);
tipc_continue(eb_ptr->bearer);
--- a/net/tipc/bearer.h
+++ b/net/tipc/bearer.h
@@ -47,6 +47,13 @@
*/
#define TIPC_MEDIA_TYPE_ETH 1

+/* 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)
+
/*
* Destination address structure used by TIPC bearers when sending messages
*
@@ -209,4 +216,13 @@ static inline int tipc_bearer_send(struc
return !b_ptr->media->send_msg(buf, b_ptr, 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 */