[PATCH net] net: openvswitch: fix leak of nested actions

[Ilya Maximets]

While parsing user-provided actions, openvswitch module may dynamically
allocate memory and store pointers in the internal copy of the actions.
So this memory has to be freed while destroying the actions.

Currently there are only two such actions: ct() and set().  However,
there are many actions that can hold nested lists of actions and
ovs_nla_free_flow_actions() just jumps over them leaking the memory.

For example, removal of the flow with the following actions will lead
to a leak of the memory allocated by nf_ct_tmpl_alloc():

  actions:clone(ct(commit),0)

Non-freed set() action may also leak the 'dst' structure for the
tunnel info including device references.

Under certain conditions with a high rate of flow rotation that may
cause significant memory leak problem (2MB per second in reporter's
case).  The problem is also hard to mitigate, because the user doesn't
have direct control over the datapath flows generated by OVS.

Fix that by iterating over all the nested actions and freeing
everything that needs to be freed recursively.

New build time assertion should protect us from this problem if new
actions will be added in the future.

Unfortunately, openvswitch module doesn't use NLA_F_NESTED, so all
attributes has to be explicitly checked.  sample() and clone() actions
are mixing extra attributes into the user-provided action list.  That
prevents some code generalization too.

Fixes: 34ae932a4036 ("openvswitch: Make tunnel set action attach a metadata dst")
Link: https://mail.openvswitch.org/pipermail/ovs-dev/2022-March/392922.html
Reported-by: Stéphane Graber <stgraber@xxxxxxxxxx>
Signed-off-by: Ilya Maximets <i.maximets@xxxxxxx>
---
 net/openvswitch/flow_netlink.c | 95 ++++++++++++++++++++++++++++++++--
 1 file changed, 90 insertions(+), 5 deletions(-)

diff --git a/net/openvswitch/flow_netlink.c b/net/openvswitch/flow_netlink.c
index dbdcaaa27f5b..7176156d3844 100644
--- a/net/openvswitch/flow_netlink.c
+++ b/net/openvswitch/flow_netlink.c
@@ -2317,6 +2317,62 @@ static struct sw_flow_actions *nla_alloc_flow_actions(int size)
 	return sfa;
 }
 
+static void ovs_nla_free_nested_actions(const struct nlattr *actions, int len);
+
+static void ovs_nla_free_check_pkt_len_action(const struct nlattr *action)
+{
+	const struct nlattr *a;
+	int rem;
+
+	nla_for_each_nested(a, action, rem) {
+		switch (nla_type(a)) {
+		case OVS_CHECK_PKT_LEN_ATTR_ACTIONS_IF_LESS_EQUAL:
+		case OVS_CHECK_PKT_LEN_ATTR_ACTIONS_IF_GREATER:
+			ovs_nla_free_nested_actions(nla_data(a), nla_len(a));
+			break;
+		}
+	}
+}
+
+static void ovs_nla_free_clone_action(const struct nlattr *action)
+{
+	const struct nlattr *a = nla_data(action);
+	int rem = nla_len(action);
+
+	switch (nla_type(a)) {
+	case OVS_CLONE_ATTR_EXEC:
+		/* The real list of actions follows this attribute. */
+		a = nla_next(a, &rem);
+		ovs_nla_free_nested_actions(a, rem);
+		break;
+	}
+}
+
+static void ovs_nla_free_dec_ttl_action(const struct nlattr *action)
+{
+	const struct nlattr *a = nla_data(action);
+
+	switch (nla_type(a)) {
+	case OVS_DEC_TTL_ATTR_ACTION:
+		ovs_nla_free_nested_actions(nla_data(a), nla_len(a));
+		break;
+	}
+}
+
+static void ovs_nla_free_sample_action(const struct nlattr *action)
+{
+	const struct nlattr *a = nla_data(action);
+	int rem = nla_len(action);
+
+	switch (nla_type(a)) {
+	case OVS_SAMPLE_ATTR_ARG:
+		/* The real list of actions follows this attribute. */
+		a = nla_next(a, &rem);
+		ovs_nla_free_nested_actions(a, rem);
+		break;
+	}
+}
+
 static void ovs_nla_free_set_action(const struct nlattr *a)
 {
 	const struct nlattr *ovs_key = nla_data(a);
@@ -2330,25 +2386,54 @@ static void ovs_nla_free_set_action(const struct nlattr *a)
 	}
 }
 
-void ovs_nla_free_flow_actions(struct sw_flow_actions *sf_acts)
+static void ovs_nla_free_nested_actions(const struct nlattr *actions, int len)
 {
 	const struct nlattr *a;
 	int rem;
 
-	if (!sf_acts)
+	/* Whenever new actions are added, the need to update this
+	 * function should be considered.
+	 */
+	BUILD_BUG_ON(OVS_ACTION_ATTR_MAX != 23);
+
+	if (!actions)
 		return;
 
-	nla_for_each_attr(a, sf_acts->actions, sf_acts->actions_len, rem) {
+	nla_for_each_attr(a, actions, len, rem) {
 		switch (nla_type(a)) {
-		case OVS_ACTION_ATTR_SET:
-			ovs_nla_free_set_action(a);
+		case OVS_ACTION_ATTR_CHECK_PKT_LEN:
+			ovs_nla_free_check_pkt_len_action(a);
+			break;
+
+		case OVS_ACTION_ATTR_CLONE:
+			ovs_nla_free_clone_action(a);
 			break;
+
 		case OVS_ACTION_ATTR_CT:
 			ovs_ct_free_action(a);
 			break;
+
+		case OVS_ACTION_ATTR_DEC_TTL:
+			ovs_nla_free_dec_ttl_action(a);
+			break;
+
+		case OVS_ACTION_ATTR_SAMPLE:
+			ovs_nla_free_sample_action(a);
+			break;
+
+		case OVS_ACTION_ATTR_SET:
+			ovs_nla_free_set_action(a);
+			break;
 		}
 	}
+}
+
+void ovs_nla_free_flow_actions(struct sw_flow_actions *sf_acts)
+{
+	if (!sf_acts)
+		return;
 
+	ovs_nla_free_nested_actions(sf_acts->actions, sf_acts->actions_len);
 	kfree(sf_acts);
 }
 
-- 
2.34.1