| Message ID | 20161201110205.10749A0F33@unicorn.suse.cz |
|---|---|
| State | Changes Requested, archived |
| Delegated to: | David Miller |
| Headers | show |
On Thu, 2016-12-01 at 12:02 +0100, Michal Kubecek wrote: [...] > +/* check if device MTU is sufficient for tipc headers */ > +static 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; > +} [...] The comment says "check if ... sufficient" but the return value indicates the opposite. Could you make these consistent? Other than that, this looks OK to me. I haven't tested any version as I don't know how to use TIPC. Ben.
On Thu, Dec 01, 2016 at 04:11:18PM +0000, Ben Hutchings wrote: > On Thu, 2016-12-01 at 12:02 +0100, Michal Kubecek wrote: > [...] > > +/* check if device MTU is sufficient for tipc headers */ > > +static 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; > > +} > [...] > > The comment says "check if ... sufficient" but the return value > indicates the opposite. Could you make these consistent? Good point. I suppose renaming the function to e.g. tipc_mtu_bad() (and rewording the commment accordingly) would also make the code more readable without looking at the definition. I'll wait for other comments and send v3 tomorrow. > Other than that, this looks OK to me. I haven't tested any version as > I don't know how to use TIPC. I checked that the patch doesn't allow enabling a bearer on top of device with insufficient MTU and it does for sufficient (100/128), both in eth and udp case. I also checked that lowering MTU under 100 in eth case disables attached bearer. I didn't run any deeper test like sending an actual traffic but the patch shouldn't affect that. Michal Kubecek
diff --git a/net/tipc/bearer.c b/net/tipc/bearer.c index 975dbeb60ab0..1c004a46486f 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 +626,11 @@ static int tipc_l2_device_event(struct notifier_block *nb, unsigned long evt, tipc_reset_bearer(net, b); break; case NETDEV_CHANGEMTU: + if (tipc_check_mtu(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..6b8a1d9d313a 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 <net/genetlink.h> #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 */ +static 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)
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 <mkubecek@suse.cz> Reported-by: Qian Zhang (张谦) <zhangqian-c@360.cn> --- 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(-)