tipc: check minimum bearer MTU

[ Upstream commit 3de81b758853f0b29c61e246679d20b513c4cfec ]

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.

References: CVE-2016-8632
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>
Conflicts:
	net/tipc/bearer.c
	net/tipc/bearer.h
due to 1a90632da8c17a27e0c93538ee987764adee43a5: tipc: eliminate remnants of hungarian notation
and b1c29f6b10d5981c89d3ea9b9991ca97141ed6d0 tipc: simplify resetting and disabling of bearers

Signed-off-by: Philipp Hahn <hahn@univention.de>
Signed-off-by: Sasha Levin <alexander.levin@verizon.com>

diff --git a/net/tipc/bearer.c b/net/tipc/bearer.c
index 70e3dacbf84ab7a899298fca1fdcb2e77fd0c2d5..bf7d6a44c6f22de3a6fed537cdcbf73f8675139c 100644 (file)
--- a/net/tipc/bearer.c
+++ b/net/tipc/bearer.c
@@ -386,6 +386,10 @@ 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);
@@ -524,14 +528,17 @@ static int tipc_l2_device_event(struct notifier_block *nb, unsigned long evt,
        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:
        case NETDEV_CHANGEMTU:
+               if (tipc_mtu_bad(dev, 0)) {
+                       bearer_disable(net, b_ptr, false);
+                       break;
+               }
+               b_ptr->mtu = dev->mtu;
                tipc_reset_bearer(net, b_ptr);
                break;
        case NETDEV_CHANGEADDR:

diff --git a/net/tipc/bearer.h b/net/tipc/bearer.h
index 5cad243ee8fc646efccfe72f26ad49ebdfe42f4f..b7302b01262440f16e4f5712c0ab939fe5e20f93 100644 (file)
--- a/net/tipc/bearer.h
+++ b/net/tipc/bearer.h
@@ -38,6 +38,7 @@
 #define _TIPC_BEARER_H
 
 #include "netlink.h"
+#include "msg.h"
 #include <net/genetlink.h>
 
 #define MAX_BEARERS    2
@@ -61,6 +62,9 @@
 #define TIPC_MEDIA_TYPE_IB     2
 #define TIPC_MEDIA_TYPE_UDP    3
 
+/* minimum bearer MTU */
+#define TIPC_MIN_BEARER_MTU    (MAX_H_SIZE + INT_H_SIZE)
+
 /**
  * struct tipc_node_map - set of node identifiers
  * @count: # of nodes in set
@@ -218,4 +222,13 @@ void tipc_bearer_stop(struct net *net);
 void tipc_bearer_send(struct net *net, 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 */

diff --git a/net/tipc/udp_media.c b/net/tipc/udp_media.c
index f8dfee5072c0ee276a3d661fcc4275eed6c27aa1..e14f23542a1a4a6028aa6e1d8a3d1fb3289e5d41 100644 (file)
--- a/net/tipc/udp_media.c
+++ b/net/tipc/udp_media.c
@@ -374,6 +374,11 @@ 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)