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
Reported-by: Qian Zhang (张谦)
---
changes v2 to v3:
- rename tipc_check_mtu() helper to tipc_mtu_bad() and make the comment
about the function less confusing
changes v1 to v2:
- add missing "static" to tipc_check_mtu() helper declaration
- rather than blocking device MTU change to too low value, disable tipc
bearer if that happens (suggested by Ben Hutchings)
---
net/tipc/bearer.c| 11 +--
net/tipc/bearer.h| 13 +
net/tipc/udp_media.c | 5 +
3 files changed, 27 insertions(+), 2 deletions(-)
diff --git a/net/tipc/bearer.c b/net/tipc/bearer.c
index 975dbeb60ab0..52d74760fb68 100644
--- a/net/tipc/bearer.c
+++ b/net/tipc/bearer.c
@@ -421,6 +421,10 @@ int tipc_enable_l2_media(struct net *net, struct
tipc_bearer *b,
dev = dev_get_by_name(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);
@@ -610,8 +614,6 @@ static int tipc_l2_device_event(struct notifier_block *nb,
unsigned long evt,
if (!b)
return NOTIFY_DONE;
- b->mtu = dev->mtu;
-
switch (evt) {
case NETDEV_CHANGE:
if (netif_carrier_ok(dev))
@@ -624,6 +626,11 @@ static int tipc_l2_device_event(struct notifier_block *nb,
unsigned long evt,
tipc_reset_bearer(net, b);
break;
case NETDEV_CHANGEMTU:
+ if (tipc_mtu_bad(dev, 0)) {
+ bearer_disable(net, b);
+ break;
+ }
+ b->mtu = dev->mtu;
tipc_reset_bearer(net, b);
break;
case NETDEV_CHANGEADDR:
diff --git a/net/tipc/bearer.h b/net/tipc/bearer.h
index 78892e2f53e3..278ff7f616f9 100644
--- a/net/tipc/bearer.h
+++ b/net/tipc/bearer.h
@@ -39,6 +39,7 @@
#include "netlink.h"
#include "core.h"
+#include "msg.h"
#include
#define MAX_MEDIA 3
@@ -59,6 +60,9 @@
#define TIPC_MEDIA_TYPE_IB 2
#define TIPC_MEDIA_TYPE_UDP3
+/* 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)
@@ -215,4 +219,13 @@ void tipc_bearer_xmit(struct net *net, u32 bearer_id,
void tipc_bearer_bc_xmit(struct net *net, u32 bearer_id,
struct sk_buff_head *xmitq);
+/* 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/udp_media.c b/net/tipc/udp_media.c
index 78cab9c5a445..b58dc95f3d35 100644
--- a/net/tipc/udp_media.c
+++ b/net/tipc/udp_media.c
@@ -697,6 +697,11 @@ static int tipc_udp_enable(struct net *net, struct
tipc_bearer *b,
udp_conf.local_ip.s_addr = htonl(INADDR_ANY);
udp_conf.use_udp_checksums = false;
ub->ifindex = dev->ifindex;
+ if (tipc_mtu_bad(dev, sizeof(struct iphdr) +
+ sizeof(struct udphdr))) {
+ err = -EINVAL;
+ goto err;
+ }
b->mtu = dev->mtu - sizeof(struct iphdr)
- sizeof(struct udphdr);
#if IS_ENABLED(CONFIG_IPV6)
--
2.10.2
