On Mon, 2019-03-18 at 19:36 +0800, Xin Long 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.
>
> Fixes: e873e4b9cc7e ("ipv6: use fib6_info_hold_safe() when necessary")
> Reported-by: Jianlin Shi <ji...@redhat.com>
> Suggested-by: Paolo Abeni <pab...@redhat.com>
> Signed-off-by: Xin Long <lucien....@gmail.com>
> ---
> net/ipv6/route.c | 14 +++++++-------
> 1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> index 4ef4bbd..754777d 100644
> --- a/net/ipv6/route.c
> +++ b/net/ipv6/route.c
> @@ -1040,13 +1040,17 @@ 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)
> + if (nrt) {
> ip6_rt_copy_init(nrt, rt);
> - else
> + } else {
> fib6_info_release(rt);
> +fallback:
> + nrt = dev_net(dev)->ipv6.ip6_null_entry;
> + dst_hold(&nrt->dst);
> + }
>
> return nrt;
> }
> @@ -1096,10 +1100,6 @@ 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();
Acked-by: Paolo Abeni <pab...@redhat.com>
