Re: [PATCH 16/18] net: mpls: prevent bounds-check bypass via speculative execution

[Sergei Shtylyov]

On 1/6/2018 4:11 AM, Dan Williams wrote:

> Static analysis reports that 'index' may be a user controlled value that
> is used as a data dependency reading 'rt' from the 'platform_label'
> array.  In order to avoid potential leaks of kernel memory values, block
> speculative execution of the instruction stream that could issue further
> reads based on an invalid 'rt' value.
>
> Based on an original patch by Elena Reshetova.
>
> Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
> Cc: Eric W. Biederman <ebiederm@xxxxxxxxxxxx>
> Cc: netdev@xxxxxxxxxxxxxxx
> Signed-off-by: Elena Reshetova <elena.reshetova@xxxxxxxxx>
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
> ---
>   net/mpls/af_mpls.c |   12 +++++++-----
>   1 file changed, 7 insertions(+), 5 deletions(-)
>
> diff --git a/net/mpls/af_mpls.c b/net/mpls/af_mpls.c
> index 8ca9915befc8..ebcf0e246cfe 100644
> --- a/net/mpls/af_mpls.c
> +++ b/net/mpls/af_mpls.c
[...]
> @@ -77,12 +78,13 @@ static void rtmsg_lfib(int event, u32 label, struct mpls_route *rt,
>   static struct mpls_route *mpls_route_input_rcu(struct net *net, unsigned index)
>   {
>   	struct mpls_route *rt = NULL;
> +	struct mpls_route __rcu **platform_label =
> +		rcu_dereference(net->mpls.platform_label);
> +	struct mpls_route __rcu **rtp;
>   
> -	if (index < net->mpls.platform_labels) {
> -		struct mpls_route __rcu **platform_label =
> -			rcu_dereference(net->mpls.platform_label);
> -		rt = rcu_dereference(platform_label[index]);
> -	}
> +	if ((rtp = nospec_array_ptr(platform_label, index,


   And here...

> +					net->mpls.platform_labels)))
> +		rt = rcu_dereference(*rtp);
>   	return rt;
>   }
>   

MBR, Sergei