netdev - [PATCH net 3/3] tipc: pass tunnel dev as NULL to udp_tunnel(6)_xmit

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Message-Id: <789f1fa42423024861f811c237738a236605d35d.1560778340.git.lucien.xin@gmail.com>
Date:   Mon, 17 Jun 2019 21:34:15 +0800
From:   Xin Long <lucien.xin@...il.com>
To:     network dev <netdev@...r.kernel.org>
Cc:     davem@...emloft.net, Jon Maloy <jon.maloy@...csson.com>,
        Ying Xue <ying.xue@...driver.com>,
        tipc-discussion@...ts.sourceforge.net,
        Marcelo Ricardo Leitner <marcelo.leitner@...il.com>,
        Neil Horman <nhorman@...driver.com>,
        Su Yanjun <suyj.fnst@...fujitsu.com>,
        David Ahern <dsahern@...il.com>,
        syzkaller-bugs@...glegroups.com,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Pravin B Shelar <pshelar@...ira.com>
Subject: [PATCH net 3/3] tipc: pass tunnel dev as NULL to udp_tunnel(6)_xmit_skb

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
  net/ipv4/route.c:1556
    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]
  ...

or:

  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
    <IRQ>
    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@...kaller.appspotmail.com
Reported-by: syzbot+a9e23ea2aa21044c2798@...kaller.appspotmail.com
Reported-by: syzbot+c4c4b2bb358bb936ad7e@...kaller.appspotmail.com
Reported-by: syzbot+0290d2290a607e035ba1@...kaller.appspotmail.com
Reported-by: syzbot+a43d8d4e7e8a7a9e149e@...kaller.appspotmail.com
Reported-by: syzbot+a47c5f4c6c00fc1ed16e@...kaller.appspotmail.com
Fixes: 039f50629b7f ("ip_tunnel: Move stats update to iptunnel_xmit()")
Signed-off-by: Xin Long <lucien.xin@...il.com>
---
 net/tipc/udp_media.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/net/tipc/udp_media.c b/net/tipc/udp_media.c
index 7fc02d8..1405ccc 100644
--- a/net/tipc/udp_media.c
+++ b/net/tipc/udp_media.c
@@ -176,7 +176,6 @@ static int tipc_udp_xmit(struct net *net, struct sk_buff *skb,
 			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, struct sk_buff *skb,
 		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);
 #endif
 	}
 	return err;
-- 
2.1.0