From 29273d459fb00a86bfb1ffed026033b152a99870 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 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 --- net/tipc/bearer.h | 16 ++++++++++++++++ net/tipc/eth_media.c | 12 ++++++++++-- 2 files changed, 26 insertions(+), 2 deletions(-) diff --git a/net/tipc/bearer.h b/net/tipc/bearer.h index d696f9e414e3..d97d03f4d31b 100644 --- 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(struct tipc_bearer *b_ptr, 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 */ diff --git a/net/tipc/eth_media.c b/net/tipc/eth_media.c index a224a38f0218..2e79e84660fb 100644 --- a/net/tipc/eth_media.c +++ b/net/tipc/eth_media.c @@ -167,6 +167,10 @@ static int enable_bearer(struct tipc_bearer *tb_ptr) 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 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)) @@ -243,6 +245,12 @@ static int recv_notification(struct notifier_block *nb, unsigned long evt, 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); -- 2.39.5