[PATCH 5.1 55/55] tipc: pass tunnel dev as NULL to udp_tunnel(6)_xmit_skb

From: Greg Kroah-Hartman
Date: Tue Jul 02 2019 - 04:04:51 EST

From: Xin Long <lucien.xin@xxxxxxxxx>

commit c3bcde026684c62d7a2b6f626dc7cf763833875c upstream.

udp_tunnel(6)_xmit_skb() called by tipc_udp_xmit() expects a tunnel device
to count packets on dev->tstats, a perpcu variable. However, TIPC is using
udp tunnel with no tunnel device, and pass the lower dev, like veth device
that only initializes dev->lstats(a perpcu variable) when creating it.

Later iptunnel_xmit_stats() called by ip(6)tunnel_xmit() thinks the dev as
a tunnel device, and uses dev->tstats instead of dev->lstats. tstats' each
pointer points to a bigger struct than lstats, so when tstats->tx_bytes is
increased, other percpu variable's members could be overwritten.

syzbot has reported quite a few crashes due to fib_nh_common percpu member
'nhc_pcpu_rth_output' overwritten, call traces are like:

BUG: KASAN: slab-out-of-bounds in rt_cache_valid+0x158/0x190
rt_cache_valid+0x158/0x190 net/ipv4/route.c:1556
__mkroute_output net/ipv4/route.c:2332 [inline]
ip_route_output_key_hash_rcu+0x819/0x2d50 net/ipv4/route.c:2564
ip_route_output_key_hash+0x1ef/0x360 net/ipv4/route.c:2393
__ip_route_output_key include/net/route.h:125 [inline]
ip_route_output_flow+0x28/0xc0 net/ipv4/route.c:2651
ip_route_output_key include/net/route.h:135 [inline]


kasan: GPF could be caused by NULL-ptr deref or user memory access
RIP: 0010:dst_dev_put+0x24/0x290 net/core/dst.c:168
rt_fibinfo_free_cpus net/ipv4/fib_semantics.c:200 [inline]
free_fib_info_rcu+0x2e1/0x490 net/ipv4/fib_semantics.c:217
__rcu_reclaim kernel/rcu/rcu.h:240 [inline]
rcu_do_batch kernel/rcu/tree.c:2437 [inline]
invoke_rcu_callbacks kernel/rcu/tree.c:2716 [inline]
rcu_process_callbacks+0x100a/0x1ac0 kernel/rcu/tree.c:2697

The issue exists since tunnel stats update is moved to iptunnel_xmit by
Commit 039f50629b7f ("ip_tunnel: Move stats update to iptunnel_xmit()"),
and here to fix it by passing a NULL tunnel dev to udp_tunnel(6)_xmit_skb
so that the packets counting won't happen on dev->tstats.

Reported-by: syzbot+9d4c12bfd45a58738d0a@xxxxxxxxxxxxxxxxxxxxxxxxx
Reported-by: syzbot+a9e23ea2aa21044c2798@xxxxxxxxxxxxxxxxxxxxxxxxx
Reported-by: syzbot+c4c4b2bb358bb936ad7e@xxxxxxxxxxxxxxxxxxxxxxxxx
Reported-by: syzbot+0290d2290a607e035ba1@xxxxxxxxxxxxxxxxxxxxxxxxx
Reported-by: syzbot+a43d8d4e7e8a7a9e149e@xxxxxxxxxxxxxxxxxxxxxxxxx
Reported-by: syzbot+a47c5f4c6c00fc1ed16e@xxxxxxxxxxxxxxxxxxxxxxxxx
Fixes: 039f50629b7f ("ip_tunnel: Move stats update to iptunnel_xmit()")
Signed-off-by: Xin Long <lucien.xin@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

net/tipc/udp_media.c | 8 +++-----
1 file changed, 3 insertions(+), 5 deletions(-)

--- a/net/tipc/udp_media.c
+++ b/net/tipc/udp_media.c
@@ -176,7 +176,6 @@ static int tipc_udp_xmit(struct net *net
goto tx_error;

- skb->dev = rt->dst.dev;
ttl = ip4_dst_hoplimit(&rt->dst);
udp_tunnel_xmit_skb(rt, ub->ubsock->sk, skb, src->ipv4.s_addr,
dst->ipv4.s_addr, 0, ttl, 0, src->port,
@@ -195,10 +194,9 @@ static int tipc_udp_xmit(struct net *net
if (err)
goto tx_error;
ttl = ip6_dst_hoplimit(ndst);
- err = udp_tunnel6_xmit_skb(ndst, ub->ubsock->sk, skb,
- ndst->dev, &src->ipv6,
- &dst->ipv6, 0, ttl, 0, src->port,
- dst->port, false);
+ err = udp_tunnel6_xmit_skb(ndst, ub->ubsock->sk, skb, NULL,
+ &src->ipv6, &dst->ipv6, 0, ttl, 0,
+ src->port, dst->port, false);
return err;