Re: [PATCH net v1] net/sched: cls_api: complement tcf_tfilter_dump_policy

[Jamal Hadi Salim]

Hi,

On Sun, Dec 24, 2023 at 11:54 AM Lin Ma <linma@xxxxxxxxxx> wrote:
>
> In function `tc_dump_tfilter`, the attributes array is parsed via
> tcf_tfilter_dump_policy which only describes TCA_DUMP_FLAGS. However,
> the NLA TCA_CHAIN is also accessed with `nla_get_u32`. According to the
> commit 5e2424708da7 ("xfrm: add forgotten nla_policy for
> XFRMA_MTIMER_THRESH"), such a missing piece could lead to a potential
> heap data leak.
>

Can you clarify what "heap data leak" you are referring to?
As much as i can see any reference to NLA_TCA_CHAIN is checked for
presence before being put to use. So far that reason I  dont see how
this patch qualifies as "net". It looks like an enhancement to me
which should target net-next, unless i am missing something obvious.

cheers,
jamal

> The access to TCA_CHAIN is introduced in commit 5bc1701881e3 ("net:
> sched: introduce multichain support for filters") and no nla_policy is
> provided for parsing at that point. Later on, tcf_tfilter_dump_policy is
> introduced in commit f8ab1807a9c9 ("net: sched: introduce terse dump
> flag") while still ignoring the fact that TCA_CHAIN needs a check. This
> patch does that by complementing the policy.
>
> Note that other functions that access TCA_CHAIN, like tc_new_tfilter,
> are not vulnerable as they choose rtm_tca_policy as the parsing policy
> which describes the TCA_CHAIN already.
>
> Fixes: 5bc1701881e3 ("net: sched: introduce multichain support for filters")
> Signed-off-by: Lin Ma <linma@xxxxxxxxxx>
> ---
>  net/sched/cls_api.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
> index 1976bd163986..2b5b8eca2ee3 100644
> --- a/net/sched/cls_api.c
> +++ b/net/sched/cls_api.c
> @@ -2732,6 +2732,7 @@ static bool tcf_chain_dump(struct tcf_chain *chain, struct Qdisc *q, u32 parent,
>  }
>
>  static const struct nla_policy tcf_tfilter_dump_policy[TCA_MAX + 1] = {
> +       [TCA_CHAIN]      = { .type = NLA_U32 },
>         [TCA_DUMP_FLAGS] = NLA_POLICY_BITFIELD32(TCA_DUMP_FLAGS_TERSE),
>  };
>
> --
> 2.17.1
>