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

[Lin Ma <linma@zju.edu.cn>]

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.

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@zju.edu.cn>
---
 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