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

Sergei Shtylyov
2018-01-06T10:06:33Z

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@davemloft.net>
> Cc: Eric W. Biederman <ebiederm@xmission.com>
> Cc: netdev@vger.kernel.org
> Signed-off-by: Elena Reshetova <elena.reshetova@intel.com>
> Signed-off-by: Dan Williams <dan.j.williams@intel.com>
> ---
> 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