net/sched: prepare TC actions to properly validate the control action

- pass a pointer to struct tcf_proto in each actions's init() handler,
  to allow validating the control action, checking whether the chain
  exists and (eventually) refcounting it.
- remove code that validates the control action after a successful call
  to the action's init() handler, and replace it with a test that forbids
  addition of actions having 'goto_chain' and NULL goto_chain pointer at
  the same time.
- add tcf_action_check_ctrlact(), that will validate the control action
  and eventually allocate the action 'goto_chain' within the init()
  handler.
- add tcf_action_set_ctrlact(), that will assign the control action and
  swap the current 'goto_chain' pointer with the new given one.

This disallows 'goto_chain' on actions that don't initialize it properly
in their init() handler, i.e. calling tcf_action_check_ctrlact() after
successful IDR reservation and then calling tcf_action_set_ctrlact()
to assign 'goto_chain' and 'tcf_action' consistently.

By doing this, the kernel does not leak anymore refcounts when a valid
'goto chain' handle is replaced in TC actions, causing kmemleak splats
like the following one:

 # tc chain add dev dd0 chain 42 ingress protocol ip flower \
 > ip_proto tcp action drop
 # tc chain add dev dd0 chain 43 ingress protocol ip flower \
 > ip_proto udp action drop
 # tc filter add dev dd0 ingress matchall \
 > action gact goto chain 42 index 66
 # tc filter replace dev dd0 ingress matchall \
 > action gact goto chain 43 index 66
 # echo scan >/sys/kernel/debug/kmemleak
 <...>
 unreferenced object 0xffff93c0ee09f000 (size 1024):
 comm "tc", pid 2565, jiffies 4295339808 (age 65.426s)
 hex dump (first 32 bytes):
   00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00  ................
   00 00 00 00 08 00 06 00 00 00 00 00 00 00 00 00  ................
 backtrace:
   [<000000009b63f92d>] tc_ctl_chain+0x3d2/0x4c0
   [<00000000683a8d72>] rtnetlink_rcv_msg+0x263/0x2d0
   [<00000000ddd88f8e>] netlink_rcv_skb+0x4a/0x110
   [<000000006126a348>] netlink_unicast+0x1a0/0x250
   [<00000000b3340877>] netlink_sendmsg+0x2c1/0x3c0
   [<00000000a25a2171>] sock_sendmsg+0x36/0x40
   [<00000000f19ee1ec>] ___sys_sendmsg+0x280/0x2f0
   [<00000000d0422042>] __sys_sendmsg+0x5e/0xa0
   [<000000007a6c61f9>] do_syscall_64+0x5b/0x180
   [<00000000ccd07542>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
   [<0000000013eaa334>] 0xffffffffffffffff

Fixes: db50514f9a9c ("net: sched: add termination action to allow goto chain")
Fixes: 97763dc0f401 ("net_sched: reject unknown tcfa_action values")
Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 56 insertions, 41 deletions

diff --git a/net/sched/act_api.c b/net/sched/act_api.c
index aecf1bf233c8..fe67b98ac641 100644
--- a/net/sched/act_api.c
+++ b/net/sched/act_api.c
@@ -28,23 +28,6 @@
 #include <net/act_api.h>
 #include <net/netlink.h>
 
-static int tcf_action_goto_chain_init(struct tc_action *a, struct tcf_proto *tp)
-{
-	u32 chain_index = a->tcfa_action & TC_ACT_EXT_VAL_MASK;
-
-	if (!tp)
-		return -EINVAL;
-	a->goto_chain = tcf_chain_get_by_act(tp->chain->block, chain_index);
-	if (!a->goto_chain)
-		return -ENOMEM;
-	return 0;
-}
-
-static void tcf_action_goto_chain_fini(struct tc_action *a)
-{
-	tcf_chain_put_by_act(a->goto_chain);
-}
-
 static void tcf_action_goto_chain_exec(const struct tc_action *a,
 				       struct tcf_result *res)
 {
@@ -71,6 +54,53 @@ static void tcf_set_action_cookie(struct tc_cookie __rcu **old_cookie,
 		call_rcu(&old->rcu, tcf_free_cookie_rcu);
 }
 
+int tcf_action_check_ctrlact(int action, struct tcf_proto *tp,
+			     struct tcf_chain **newchain,
+			     struct netlink_ext_ack *extack)
+{
+	int opcode = TC_ACT_EXT_OPCODE(action), ret = -EINVAL;
+	u32 chain_index;
+
+	if (!opcode)
+		ret = action > TC_ACT_VALUE_MAX ? -EINVAL : 0;
+	else if (opcode <= TC_ACT_EXT_OPCODE_MAX || action == TC_ACT_UNSPEC)
+		ret = 0;
+	if (ret) {
+		NL_SET_ERR_MSG(extack, "invalid control action");
+		goto end;
+	}
+
+	if (TC_ACT_EXT_CMP(action, TC_ACT_GOTO_CHAIN)) {
+		chain_index = action & TC_ACT_EXT_VAL_MASK;
+		if (!tp || !newchain) {
+			ret = -EINVAL;
+			NL_SET_ERR_MSG(extack,
+				       "can't goto NULL proto/chain");
+			goto end;
+		}
+		*newchain = tcf_chain_get_by_act(tp->chain->block, chain_index);
+		if (!*newchain) {
+			ret = -ENOMEM;
+			NL_SET_ERR_MSG(extack,
+				       "can't allocate goto_chain");
+		}
+	}
+end:
+	return ret;
+}
+EXPORT_SYMBOL(tcf_action_check_ctrlact);
+
+struct tcf_chain *tcf_action_set_ctrlact(struct tc_action *a, int action,
+					 struct tcf_chain *newchain)
+{
+	struct tcf_chain *oldchain = a->goto_chain;
+
+	a->tcfa_action = action;
+	a->goto_chain = newchain;
+	return oldchain;
+}
+EXPORT_SYMBOL(tcf_action_set_ctrlact);
+
 /* XXX: For standalone actions, we don't need a RCU grace period either, because
  * actions are always connected to filters and filters are already destroyed in
  * RCU callbacks, so after a RCU grace period actions are already disconnected
@@ -78,13 +108,15 @@ static void tcf_set_action_cookie(struct tc_cookie __rcu **old_cookie,
  */
 static void free_tcf(struct tc_action *p)
 {
+	struct tcf_chain *chain = p->goto_chain;
+
 	free_percpu(p->cpu_bstats);
 	free_percpu(p->cpu_bstats_hw);
 	free_percpu(p->cpu_qstats);
 
 	tcf_set_action_cookie(&p->act_cookie, NULL);
-	if (p->goto_chain)
-		tcf_action_goto_chain_fini(p);
+	if (chain)
+		tcf_chain_put_by_act(chain);
 
 	kfree(p);
 }
@@ -800,15 +832,6 @@ static struct tc_cookie *nla_memdup_cookie(struct nlattr **tb)
 	return c;
 }
 
-static 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;
-}
-
 struct tc_action *tcf_action_init_1(struct net *net, struct tcf_proto *tp,
 				    struct nlattr *nla, struct nlattr *est,
 				    char *name, int ovr, int bind,
@@ -890,10 +913,10 @@ struct tc_action *tcf_action_init_1(struct net *net, struct tcf_proto *tp,
 	/* backward compatibility for policer */
 	if (name == NULL)
 		err = a_o->init(net, tb[TCA_ACT_OPTIONS], est, &a, ovr, bind,
-				rtnl_held, extack);
+				rtnl_held, tp, extack);
 	else
 		err = a_o->init(net, nla, est, &a, ovr, bind, rtnl_held,
-				extack);
+				tp, extack);
 	if (err < 0)
 		goto err_mod;
 
@@ -907,18 +930,10 @@ struct tc_action *tcf_action_init_1(struct net *net, struct tcf_proto *tp,
 	if (err != ACT_P_CREATED)
 		module_put(a_o->owner);
 
-	if (TC_ACT_EXT_CMP(a->tcfa_action, TC_ACT_GOTO_CHAIN)) {
-		err = tcf_action_goto_chain_init(a, tp);
-		if (err) {
-			tcf_action_destroy_1(a, bind);
-			NL_SET_ERR_MSG(extack, "Failed to init TC action chain");
-			return ERR_PTR(err);
-		}
-	}
-
-	if (!tcf_action_valid(a->tcfa_action)) {
+	if (TC_ACT_EXT_CMP(a->tcfa_action, TC_ACT_GOTO_CHAIN) &&
+	    !a->goto_chain) {
 		tcf_action_destroy_1(a, bind);
-		NL_SET_ERR_MSG(extack, "Invalid control action value");
+		NL_SET_ERR_MSG(extack, "can't use goto chain with NULL chain");
 		return ERR_PTR(-EINVAL);
 	}