[Trusty SRU][CVE-2016-8632][PATCH 1/1] tipc: check minimum bearer MTU

[Kleber Sacilotto de Souza]

From: Michal Kubeček <mkubecek at suse.cz>

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 at suse.cz>
Reported-by: Qian Zhang (张谦) <zhangqian-c at 360.cn>
Acked-by: Ying Xue <ying.xue at windriver.com>
Signed-off-by: David S. Miller <davem at davemloft.net>

CVE-2016-8632
(backported from commit 3de81b758853f0b29c61e246679d20b513c4cfec)
[kleber:
 - Adjust context
 - Duplicate macro definitions in bearer.h to avoid mutual inclusion
 - Duplicate bearer changes for eth and ib media
 - Drop changes in udp_media.c]
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza at canonical.com>
---
 net/tipc/bearer.h    | 16 ++++++++++++++++
 net/tipc/eth_media.c | 11 +++++++++--
 net/tipc/ib_media.c  | 11 +++++++++--
 3 files changed, 34 insertions(+), 4 deletions(-)

diff --git a/net/tipc/bearer.h b/net/tipc/bearer.h
index e5e04be6fffa..cc8bc3b7cb6f 100644
--- a/net/tipc/bearer.h
+++ b/net/tipc/bearer.h
@@ -58,6 +58,13 @@
 #define TIPC_MEDIA_TYPE_ETH	1
 #define TIPC_MEDIA_TYPE_IB	2
 
+/* 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)
+
 /**
  * struct tipc_media_addr - destination address used by TIPC bearers
  * @value: address info (format defined by media)
@@ -210,4 +217,13 @@ static inline void tipc_bearer_send(struct tipc_bearer *b, struct sk_buff *buf,
 	b->media->send_msg(buf, b, 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 */
diff --git a/net/tipc/eth_media.c b/net/tipc/eth_media.c
index f80d59f5a161..3fe074af15ec 100644
--- a/net/tipc/eth_media.c
+++ b/net/tipc/eth_media.c
@@ -180,6 +180,10 @@ static int enable_media(struct tipc_bearer *tb_ptr)
 	dev = dev_get_by_name(&init_net, driver_name);
 	if (!dev)
 		return -ENODEV;
+	if (tipc_mtu_bad(dev, 0)) {
+		dev_put(dev);
+		return -EINVAL;
+	}
 
 	/* Create Ethernet bearer for device */
 	eb_ptr->dev = dev;
@@ -258,8 +262,6 @@ static int recv_notification(struct notifier_block *nb, unsigned long evt,
 	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))
@@ -274,6 +276,11 @@ static int recv_notification(struct notifier_block *nb, unsigned long evt,
 		tipc_block_bearer(eb_ptr->bearer);
 		break;
 	case NETDEV_CHANGEMTU:
+		if (tipc_mtu_bad(dev, 0)) {
+			tipc_disable_bearer(eb_ptr->bearer->name);
+			break;
+		}
+		eb_ptr->bearer->mtu = dev->mtu;
 	case NETDEV_CHANGEADDR:
 		tipc_block_bearer(eb_ptr->bearer);
 		tipc_continue(eb_ptr->bearer);
diff --git a/net/tipc/ib_media.c b/net/tipc/ib_media.c
index c13989297464..c34380b9357c 100644
--- a/net/tipc/ib_media.c
+++ b/net/tipc/ib_media.c
@@ -173,6 +173,10 @@ static int enable_media(struct tipc_bearer *tb_ptr)
 	dev = dev_get_by_name(&init_net, driver_name);
 	if (!dev)
 		return -ENODEV;
+	if (tipc_mtu_bad(dev, 0)) {
+		dev_put(dev);
+		return -EINVAL;
+	}
 
 	/* Create InfiniBand bearer for device */
 	ib_ptr->dev = dev;
@@ -251,8 +255,6 @@ static int recv_notification(struct notifier_block *nb, unsigned long evt,
 	if (!ib_ptr->bearer)
 		return NOTIFY_DONE;		/* bearer had been disabled */
 
-	ib_ptr->bearer->mtu = dev->mtu;
-
 	switch (evt) {
 	case NETDEV_CHANGE:
 		if (netif_carrier_ok(dev))
@@ -267,6 +269,11 @@ static int recv_notification(struct notifier_block *nb, unsigned long evt,
 		tipc_block_bearer(ib_ptr->bearer);
 		break;
 	case NETDEV_CHANGEMTU:
+		if (tipc_mtu_bad(dev, 0)) {
+			tipc_disable_bearer(ib_ptr->bearer->name);
+			break;
+		}
+		ib_ptr->bearer->mtu = dev->mtu;
 	case NETDEV_CHANGEADDR:
 		tipc_block_bearer(ib_ptr->bearer);
 		tipc_continue(ib_ptr->bearer);
-- 
2.14.1