netdev - Re: [PATCHv2 net] ipv6: make ip6_create_rt_rcu return ip6_null

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Message-ID: <CAEA6p_A90Jt43BUwkT2nY==R9uO96uHE3ziWr9SY30_nuGuJjg@mail.gmail.com>
Date:   Wed, 20 Mar 2019 09:52:23 -0700
From:   Wei Wang <weiwan@...gle.com>
To:     Xin Long <lucien.xin@...il.com>
Cc:     network dev <netdev@...r.kernel.org>,
        "David S . Miller" <davem@...emloft.net>,
        David Ahern <dsahern@...il.com>,
        Paolo Abeni <pabeni@...hat.com>
Subject: Re: [PATCHv2 net] ipv6: make ip6_create_rt_rcu return ip6_null_entry
 instead of NULL

On Tue, Mar 19, 2019 at 11:45 PM Xin Long <lucien.xin@...il.com> wrote:
>
> 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: e873e4b9cc7e ("ipv6: use fib6_info_hold_safe() when necessary")
> Reported-by: Jianlin Shi <jishi@...hat.com>
> Suggested-by: Paolo Abeni <pabeni@...hat.com>
> Signed-off-by: Xin Long <lucien.xin@...il.com>
> ---
Acked-by: Wei Wang <weiwan@...gle.com>

Thanks for the fix.

>  net/ipv6/route.c | 18 ++++++++++--------
>  1 file changed, 10 insertions(+), 8 deletions(-)
>
> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> index 4ef4bbd..0302e0eb 100644
> --- a/net/ipv6/route.c
> +++ b/net/ipv6/route.c
> @@ -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 @@ static struct rt6_info *ip6_pol_route_lookup(struct net *net,
>                 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();
> --
> 2.1.0
>