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[73.241.150.70]) by smtp.gmail.com with ESMTPSA id h20sm71807118pfj.40.2019.04.14.15.29.31 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Sun, 14 Apr 2019 15:29:32 -0700 (PDT) Subject: Re: [PATCH net] route: Avoid crash from dereferencing NULL rt->from To: Jonathan Lemon , netdev@vger.kernel.org, dsahern@gmail.com Cc: kernel-team@fb.com References: <20190414212129.2306318-1-jonathan.lemon@gmail.com> From: Eric Dumazet Message-ID: Date: Sun, 14 Apr 2019 15:29:30 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20190414212129.2306318-1-jonathan.lemon@gmail.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On 04/14/2019 02:21 PM, 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] > [ 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] > > Signed-off-by: Jonathan Lemon > --- > 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; > + } > nrt6 = ip6_rt_cache_alloc(from, daddr, saddr); > if (nrt6) { > rt6_do_update_pmtu(nrt6, mtu); > Interesting... Please take the time to track the bug origin for your patches, thanks ! Fixes: a68886a69180 ("net/ipv6: Make from in rt6_info rcu protected") Reviewed-by: Eric Dumazet