net/neighbour: fix potential null pointer deference

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@gmail.com>
---
 net/core/neighbour.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

On 31.05.2019 11:29, 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").

Have you seen this in real life?
I see nobody who could produce neighbour with null device pointer._

> 
> Signed-off-by: Young Xiao <92siuyang@gmail.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;
>

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@gmail.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

On 5/31/19 1:29 AM, 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@gmail.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;
> 

When was the bug added exactly ?

Hint : We want a Fixes: tag, so that we can fully understand the issue and make sure the
fix is complete.

Otherwise, your patch might very well have been randomly generated by a bot.

Thank you.