From 65d30f7545ffdddcf10a59f3e54b032c5ade2e9d Mon Sep 17 00:00:00 2001 From: =?utf8?q?Michal=20Kube=C4=8Dek?= Date: Fri, 2 Dec 2016 09:33:41 +0100 Subject: [PATCH] tipc: check minimum bearer MTU MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit commit 3de81b758853f0b29c61e246679d20b513c4cfec upstream. Qian Zhang (å¼ è°¦) 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 (å¼ è°¦) Acked-by: Ying Xue Signed-off-by: David S. Miller [bwh: Backported to 4.4: - Adjust context - NETDEV_GOING_DOWN and NETDEV_CHANGEMTU cases in net notifier were combined] Signed-off-by: Ben Hutchings Signed-off-by: Greg Kroah-Hartman --- net/tipc/bearer.c | 13 +++++++++++-- net/tipc/bearer.h | 13 +++++++++++++ net/tipc/udp_media.c | 5 +++++ 3 files changed, 29 insertions(+), 2 deletions(-) diff --git a/net/tipc/bearer.c b/net/tipc/bearer.c index 648f2a67f314..cb1381513c82 100644 --- a/net/tipc/bearer.c +++ b/net/tipc/bearer.c @@ -381,6 +381,10 @@ 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); @@ -570,14 +574,19 @@ 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_GOING_DOWN: + tipc_reset_bearer(net, b_ptr); + break; case NETDEV_CHANGEMTU: + if (tipc_mtu_bad(dev, 0)) { + bearer_disable(net, b_ptr); + 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 552185bc4773..5f11e18b1fa1 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 @@ -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 @@ -226,4 +230,13 @@ 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 4056798c54a5..78d6b78de29d 100644 --- a/net/tipc/udp_media.c +++ b/net/tipc/udp_media.c @@ -376,6 +376,11 @@ 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) -- 2.34.1