Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S964782AbcK3J5w (ORCPT ); Wed, 30 Nov 2016 04:57:52 -0500 Received: from mx2.suse.de ([195.135.220.15]:39267 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757409AbcK3J5I (ORCPT ); Wed, 30 Nov 2016 04:57:08 -0500 From: Michal Kubecek Subject: [PATCH net] tipc: check minimum bearer MTU MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit To: Jon Maloy , Ying Xue Cc: "David S. Miller" , tipc-discussion@lists.sourceforge.net, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Ben Hutchings , Qian Zhang Message-Id: <20161130095702.DD033A0F14@unicorn.suse.cz> Date: Wed, 30 Nov 2016 10:57:02 +0100 (CET) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3559 Lines: 109 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) --- net/tipc/bearer.c | 9 +++++++-- net/tipc/bearer.h | 13 +++++++++++++ net/tipc/udp_media.c | 5 +++++ 3 files changed, 25 insertions(+), 2 deletions(-) diff --git a/net/tipc/bearer.c b/net/tipc/bearer.c index 975dbeb60ab0..dd4b19e8bb43 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_check_mtu(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 +626,9 @@ static int tipc_l2_device_event(struct notifier_block *nb, unsigned long evt, tipc_reset_bearer(net, b); break; case NETDEV_CHANGEMTU: + if (tipc_check_mtu(dev, 0)) + return -EINVAL; + 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..1a0b7434ec24 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_UDP 3 +/* 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 sufficient for tipc headers */ +inline bool tipc_check_mtu(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..376ed3e3ed46 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_check_mtu(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