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Date:   Wed, 2 Jan 2019 08:59:20 -0700
From:   David Ahern <dsahern@...il.com>
To:     Stefano Brivio <sbrivio@...hat.com>,
        "David S. Miller" <davem@...emloft.net>
Cc:     Jianlin Shi <jishi@...hat.com>, netdev@...r.kernel.org
Subject: Re: [PATCH net] ipv6: route: Fix return value of ip6_neigh_lookup()
 on neigh_create() error

On 1/2/19 5:29 AM, Stefano Brivio wrote:
> In ip6_neigh_lookup(), we must not return errors coming from
> neigh_create(): if creation of a neighbour entry fails, the lookup should
> return NULL, in the same way as it's done in __neigh_lookup().
> 
> Otherwise, callers legitimately checking for a non-NULL return value of
> the lookup function might dereference an invalid pointer.
> 
> For instance, on neighbour table overflow, ndisc_router_discovery()
> crashes ndisc_update() by passing ERR_PTR(-ENOBUFS) as 'neigh' argument.
> 
> Reported-by: Jianlin Shi <jishi@...hat.com>
> Fixes: f8a1b43b709d ("net/ipv6: Create a neigh_lookup for FIB entries")
> Signed-off-by: Stefano Brivio <sbrivio@...hat.com>
> ---
>  net/ipv6/route.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/net/ipv6/route.c b/net/ipv6/route.c
> index a94e0b02a8ac..40b225f87d5e 100644
> --- a/net/ipv6/route.c
> +++ b/net/ipv6/route.c
> @@ -210,7 +210,9 @@ struct neighbour *ip6_neigh_lookup(const struct in6_addr *gw,
>  	n = __ipv6_neigh_lookup(dev, daddr);
>  	if (n)
>  		return n;
> -	return neigh_create(&nd_tbl, daddr, dev);
> +
> +	n = neigh_create(&nd_tbl, daddr, dev);
> +	return IS_ERR(n) ? NULL : n;
>  }
>  
>  static struct neighbour *ip6_dst_neigh_lookup(const struct dst_entry *dst,
> 

I see now -- dst_neigh_lookup handles that check and I forgot to add the
same to the new ip6_neigh_lookup.

Thanks for the patch.

Reviewed-by: David Ahern <dsahern@...il.com>

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