netdev - Re: [PATCH] net/neighbour: fix potential null pointer deference

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Date:   Fri, 31 May 2019 10:42:25 +0200
From:   Paolo Abeni <pabeni@...hat.com>
To:     Young Xiao <92siuyang@...il.com>, davem@...emloft.net,
        dsahern@...il.com, roopa@...ulusnetworks.com, christian@...uner.io,
        khlebnikov@...dex-team.ru, netdev@...r.kernel.org
Subject: Re: [PATCH] net/neighbour: fix potential null pointer deference

On Fri, 2019-05-31 at 16:29 +0800, Young Xiao wrote:
> There is a possible null pointer deference bugs in neigh_fill_info(),
> which is similar to the bug which was fixed in commit 6adc5fd6a142
> ("net/neighbour: fix crash at dumping device-agnostic proxy entries").
> 
> Signed-off-by: Young Xiao <92siuyang@...il.com>
> ---
>  net/core/neighbour.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/net/core/neighbour.c b/net/core/neighbour.c
> index dfa8710..33c3ff1 100644
> --- a/net/core/neighbour.c
> +++ b/net/core/neighbour.c
> @@ -2440,7 +2440,7 @@ static int neigh_fill_info(struct sk_buff *skb, struct neighbour *neigh,
>  	ndm->ndm_pad2    = 0;
>  	ndm->ndm_flags	 = neigh->flags;
>  	ndm->ndm_type	 = neigh->type;
> -	ndm->ndm_ifindex = neigh->dev->ifindex;
> +	ndm->ndm_ifindex = neigh->dev ? neigh->dev->ifindex : 0;
>  
>  	if (nla_put(skb, NDA_DST, neigh->tbl->key_len, neigh->primary_key))
>  		goto nla_put_failure;

AFAICS, neigh->dev is requested to be != NULL at neighbour creation
time (see ___neigh_create()), so the above NULL ptr dereference looks
impossible. Am I missing something?

Thanks,

Paolo