netdev - Re: [PATCH net] route: Avoid crash from dereferencing NULL rt->from

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Date:   Mon, 15 Apr 2019 15:36:29 +0000
From:   Martin Lau <kafai@...com>
To:     Jonathan Lemon <jonathan.lemon@...il.com>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "dsahern@...il.com" <dsahern@...il.com>,
        Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH net] route: Avoid crash from dereferencing NULL rt->from

On Sun, Apr 14, 2019 at 02:21:29PM -0700, Jonathan Lemon wrote:
> 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>
> 
> Signed-off-by: Jonathan Lemon <jonathan.lemon@...il.com>
> ---
>  net/ipv6/route.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> index d555edaaff13..b9cbe6815f2c 100644
> --- a/net/ipv6/route.c
> +++ b/net/ipv6/route.c
> @@ -2331,6 +2331,10 @@ static void __ip6_rt_update_pmtu(struct dst_entry *dst, const struct sock *sk,
>  
>  		rcu_read_lock();
>  		from = rcu_dereference(rt6->from);
> +		if (!from) {
> +			rcu_read_unlock();
> +			return;
> +		}
Reviewed-by: Martin KaFai Lau <kafai@...com>