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net/sched: act_gact, act_police: range check the fallback control action

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tcf_action_check_ctrlact() range checks the primary control action:

	if (!opcode)
		ret = action > TC_ACT_VALUE_MAX ? -EINVAL : 0;

TC_ACT_VALUE_MAX is TC_ACT_TRAP, so kernel-internal verdicts above it
cannot be set that way. But act_gact and act_police each carry a second,
independent control action supplied by user space that never reaches that
helper - TCA_GACT_PROB.paction and TCA_POLICE_RESULT. Both only reject
TC_ACT_GOTO_CHAIN, so any other value is stored verbatim and returned
verbatim from the action.

In particular user space can store TC_ACT_CONSUMED, which is
TC_ACT_VALUE_MAX + 1 and is deliberately not part of the UAPI value
range. That verdict tells every caller the action took ownership of the
skb, so nobody frees it: sch_handle_ingress(), sch_handle_egress() and
tcf_qevent_handle() all deliberately skip the free for it. The result is
one leaked sk_buff plus its data buffer per packet traversing the filter,
unbounded, for all traffic on the chain including kernel-generated
packets.

Both are trivially deterministic. act_gact clamps tcfg_pval to >= 1, so
with pval = 1 gact_determ() returns the fallback for every packet.
act_police has no mandatory rate, so rate = 0 leaves tcfp_mtu = ~0 and
tcf_police_mtu_check() always passes.

TC_ACT_CONSUMED was added by commit 720f22fed8 ("net: sched: refactor
reinsert action"), after both goto-chain guards were written:
commit 9469f375ab ("net/sched: act_gact: disallow 'goto chain' on
fallback control action") and
commit c08f5ed5d6 ("net/sched: act_police: disallow 'goto chain' on
fallback control action"). Neither guard was widened when the new
verdict appeared.

Factor the existing range test out of tcf_action_check_ctrlact() as
tcf_action_valid() and apply it to both fallbacks. The helper cannot call
tcf_action_check_ctrlact() directly because that also allocates a
goto_chain, which is exactly what these two sites must not do.

Reproduced on v7.2-rc6: kmemleak reports one leaked 232-byte
skbuff_head_cache object plus its 704-byte data buffer per packet. With
this patch both configurations are rejected with -EINVAL and kmemleak
reports none.

Fixes: 720f22fed8 ("net: sched: refactor reinsert action")
Cc: stable@vger.kernel.org # v5.3+
Signed-off-by: Hyunjung Ko <hj351016@gmail.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Tested-by: Victor Nogueira <victor@mojatatu.com>
Link: https://patch.msgid.link/20260806101252.809593-1-hj351016@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Hyunjung Ko 2026-08-06 19:12:52 +09:00 committed by Jakub Kicinski
parent 60db47f02b
commit 883b56ae58
3 changed files with 30 additions and 0 deletions
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19
include/net/act_api.h
View File

@ -270,6 +270,25 @@ int tcf_action_check_ctrlact(int action, struct tcf_proto *tp,
struct tcf_chain *tcf_action_set_ctrlact(struct tc_action *a, int action,
struct tcf_chain *newchain);
/* Range check for a control action supplied by user space.
*
* This is the same test tcf_action_check_ctrlact() applies to the primary
* control action, factored out for the *fallback* control actions
* (act_gact's TCA_GACT_PROB.paction and act_police's TCA_POLICE_RESULT),
* which must not reach tcf_action_check_ctrlact() because they have no
* goto_chain to allocate. Without it, user space can store kernel-internal
* verdicts such as TC_ACT_CONSUMED, which is TC_ACT_VALUE_MAX + 1 and is
* deliberately not part of the UAPI value range.
*/
static inline bool tcf_action_valid(int action)
{
int opcode = TC_ACT_EXT_OPCODE(action);
if (!opcode)
return action <= TC_ACT_VALUE_MAX;
return opcode <= TC_ACT_EXT_OPCODE_MAX || action == TC_ACT_UNSPEC;
}
#ifdef CONFIG_INET
DECLARE_STATIC_KEY_FALSE(tcf_frag_xmit_count);
#endif

5
net/sched/act_gact.c
View File

@ -89,6 +89,11 @@ static int tcf_gact_init(struct net *net, struct nlattr *nla,
p_parm = nla_data(tb[TCA_GACT_PROB]);
if (p_parm->ptype >= MAX_RAND)
return -EINVAL;
if (!tcf_action_valid(p_parm->paction)) {
NL_SET_ERR_MSG(extack,
"invalid fallback control action");
return -EINVAL;
}
if (TC_ACT_EXT_CMP(p_parm->paction, TC_ACT_GOTO_CHAIN)) {
NL_SET_ERR_MSG(extack,
"goto chain not allowed on fallback");

6
net/sched/act_police.c
View File

@ -128,6 +128,12 @@ static int tcf_police_init(struct net *net, struct nlattr *nla,
if (tb[TCA_POLICE_RESULT]) {
tcfp_result = nla_get_u32(tb[TCA_POLICE_RESULT]);
if (!tcf_action_valid(tcfp_result)) {
NL_SET_ERR_MSG(extack,
"invalid fallback control action");
err = -EINVAL;
goto failure;
}
if (TC_ACT_EXT_CMP(tcfp_result, TC_ACT_GOTO_CHAIN)) {
NL_SET_ERR_MSG(extack,
"goto chain not allowed on fallback");