Commit 1c87e79a authored Mar 20, 2019 by Xin Long Committed by David S. Miller Mar 20, 2019

ipv6: make ip6_create_rt_rcu return ip6_null_entry instead of NULL



Jianlin reported a crash:

  [  381.484332] BUG: unable to handle kernel NULL pointer dereference at 0000000000000068
  [  381.619802] RIP: 0010:fib6_rule_lookup+0xa3/0x160
  [  382.009615] Call Trace:
  [  382.020762]  <IRQ>
  [  382.030174]  ip6_route_redirect.isra.52+0xc9/0xf0
  [  382.050984]  ip6_redirect+0xb6/0xf0
  [  382.066731]  icmpv6_notify+0xca/0x190
  [  382.083185]  ndisc_redirect_rcv+0x10f/0x160
  [  382.102569]  ndisc_rcv+0xfb/0x100
  [  382.117725]  icmpv6_rcv+0x3f2/0x520
  [  382.133637]  ip6_input_finish+0xbf/0x460
  [  382.151634]  ip6_input+0x3b/0xb0
  [  382.166097]  ipv6_rcv+0x378/0x4e0

It was caused by the lookup function __ip6_route_redirect() returns NULL in
fib6_rule_lookup() when ip6_create_rt_rcu() returns NULL.

So we fix it by simply making ip6_create_rt_rcu() return ip6_null_entry
instead of NULL.

v1->v2:
  - move down 'fallback:' to make it more readable.

Fixes: e873e4b9 ("ipv6: use fib6_info_hold_safe() when necessary")
Reported-by: Jianlin Shi <jishi@redhat.com>
Suggested-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Xin Long <lucien.xin@gmail.com>
Reviewed-by: David Ahern <dsahern@gmail.com>
Acked-by: Wei Wang <weiwan@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 398f0132

net/ipv6/route.c

+10 −8

Original line number	Diff line number	Diff line
		@@ -1040,14 +1040,20 @@ static struct rt6_info ip6_create_rt_rcu(struct fib6_info rt)
		struct rt6_info *nrt;

		if (!fib6_info_hold_safe(rt))
		return NULL;
		goto fallback;

		nrt = ip6_dst_alloc(dev_net(dev), dev, flags);
		if (nrt)
		ip6_rt_copy_init(nrt, rt);
		else
		if (!nrt) {
		fib6_info_release(rt);
		goto fallback;
		}

		ip6_rt_copy_init(nrt, rt);
		return nrt;

		fallback:
		nrt = dev_net(dev)->ipv6.ip6_null_entry;
		dst_hold(&nrt->dst);
		return nrt;
		}

		@@ -1096,10 +1102,6 @@ restart:
		dst_hold(&rt->dst);
		} else {
		rt = ip6_create_rt_rcu(f6i);
		if (!rt) {
		rt = net->ipv6.ip6_null_entry;
		dst_hold(&rt->dst);
		}
		}

		rcu_read_unlock();

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