[PATCH 4.19 19/96] route: Avoid crash from dereferencing NULL rt->from

Greg Kroah-Hartman
2019-04-24T17:29:56Z

From: Jonathan Lemon <jonathan.lemon@gmail.com>

[ Upstream commit 9c69a13205151c0d801de9f9d83a818e6e8f60ec ]

When __ip6_rt_update_pmtu() is called, rt->from is RCU dereferenced, but is
never checked for null - rt6_flush_exceptions() may have removed the entry.

[ 1913.989004] RIP: 0010:ip6_rt_cache_alloc+0x13/0x170
[ 1914.209410] Call Trace:
[ 1914.214798] <IRQ>
[ 1914.219226] __ip6_rt_update_pmtu+0xb0/0x190
[ 1914.228649] ip6_tnl_xmit+0x2c2/0x970 [ip6_tunnel]
[ 1914.239223] ? ip6_tnl_parse_tlv_enc_lim+0x32/0x1a0 [ip6_tunnel]
[ 1914.252489] ? __gre6_xmit+0x148/0x530 [ip6_gre]
[ 1914.262678] ip6gre_tunnel_xmit+0x17e/0x3c7 [ip6_gre]
[ 1914.273831] dev_hard_start_xmit+0x8d/0x1f0
[ 1914.283061] sch_direct_xmit+0xfa/0x230
[ 1914.291521] __qdisc_run+0x154/0x4b0
[ 1914.299407] net_tx_action+0x10e/0x1f0
[ 1914.307678] __do_softirq+0xca/0x297
[ 1914.315567] irq_exit+0x96/0xa0
[ 1914.322494] smp_apic_timer_interrupt+0x68/0x130
[ 1914.332683] apic_timer_interrupt+0xf/0x20
[ 1914.341721] </IRQ>

Fixes: a68886a69180 ("net/ipv6: Make from in rt6_info rcu protected")
Signed-off-by: Jonathan Lemon <jonathan.lemon@gmail.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Reviewed-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/ipv6/route.c | 4 ++++
1 file changed, 4 insertions(+)

--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -2367,6 +2367,10 @@ static void __ip6_rt_update_pmtu(struct

rcu_read_lock();
from = rcu_dereference(rt6->from);
+ if (!from) {
+ rcu_read_unlock();
+ return;
+ }
nrt6 = ip6_rt_cache_alloc(from, daddr, saddr);
if (nrt6) {
rt6_do_update_pmtu(nrt6, mtu);