On Wed, Jan 10, 2018 at 06:20:41PM +0100, Lorenzo Bianconi wrote:
> Set l2specific_len according to the L2-Specific Sublayer type specified
> by the userspace and not rely on a user supplied value for sublayer len
> since invalid usage of L2TP_ATTR_L2SPEC_LEN allows leaking memory on the
> network and sending corrupted frames.
> Moreover add a sanity check on l2specific_type provided by userspace
>
> Signed-off-by: Lorenzo Bianconi <lorenzo.bianc...@redhat.com>
> ---
> net/l2tp/l2tp_netlink.c | 21 ++++++++++++++++-----
> 1 file changed, 16 insertions(+), 5 deletions(-)
>
> diff --git a/net/l2tp/l2tp_netlink.c b/net/l2tp/l2tp_netlink.c
> index 48b5bf30ec50..404e5482c4e7 100644
> --- a/net/l2tp/l2tp_netlink.c
> +++ b/net/l2tp/l2tp_netlink.c
> @@ -550,13 +550,24 @@ static int l2tp_nl_cmd_session_create(struct sk_buff
> *skb, struct genl_info *inf
> if (info->attrs[L2TP_ATTR_DATA_SEQ])
> cfg.data_seq =
> nla_get_u8(info->attrs[L2TP_ATTR_DATA_SEQ]);
>
> - cfg.l2specific_type = L2TP_L2SPECTYPE_DEFAULT;
> - if (info->attrs[L2TP_ATTR_L2SPEC_TYPE])
> + if (info->attrs[L2TP_ATTR_L2SPEC_TYPE]) {
> cfg.l2specific_type =
> nla_get_u8(info->attrs[L2TP_ATTR_L2SPEC_TYPE]);
>
> - cfg.l2specific_len = 4;
> - if (info->attrs[L2TP_ATTR_L2SPEC_LEN])
> - cfg.l2specific_len =
> nla_get_u8(info->attrs[L2TP_ATTR_L2SPEC_LEN]);
> + switch (cfg.l2specific_type) {
> + case L2TP_L2SPECTYPE_DEFAULT:
> + cfg.l2specific_len = 4;
> + break;
> + case L2TP_L2SPECTYPE_NONE:
> + cfg.l2specific_len = 0;
> + break;
> + default:
> + ret = -EINVAL;
> + goto out_tunnel;
> + }
> + } else {
> + cfg.l2specific_type = L2TP_L2SPECTYPE_DEFAULT;
> + cfg.l2specific_len = 4;
> + }
>
> if (info->attrs[L2TP_ATTR_COOKIE]) {
> u16 len = nla_len(info->attrs[L2TP_ATTR_COOKIE]);
>
I think we can go one step further and remove .l2specific_len from
struct l2tp_session and struct l2tp_session_cfg. We never need this
information. Then we can start ignoring the L2TP_ATTR_L2SPEC_LEN
attribute just like we've done with L2TP_ATTR_OFFSET.
