net/sched: user-space can't set unknown tcfa_action values

Currently, when initializing an action, the user-space can specify
and use arbitrary values for the tcfa_action field. If the value
is unknown by the kernel, is implicitly threaded as TC_ACT_UNSPEC.

This change explicitly checks for unknown values at action creation
time, and explicitly convert them to TC_ACT_UNSPEC. No functional
changes are introduced, but this will allow introducing tcfa_action
values not exposed to user-space in a later patch.

Note: we can't use the above to hide TC_ACT_REDIRECT from user-space,
as the latter is already part of uAPI.

v3 -> v4:
 - use an helper to check for action validity (JiriP)
 - emit an extack for invalid actions (JiriP)
v4 -> v5:
 - keep messages on a single line, drop net_warn (Marcelo)
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/uapi/linux/pkt_cls.h

@@ -45,6 +45,7 @@ enum {
 				   * the skb and act like everything
 				   * is alright.
 				   */
+#define TC_ACT_VALUE_MAX	TC_ACT_TRAP
 
 /* There is a special kind of actions called "extended actions",
  * which need a value parameter. These have a local opcode located in
@@ -55,11 +56,12 @@ enum {
 #define __TC_ACT_EXT_SHIFT 28
 #define __TC_ACT_EXT(local) ((local) << __TC_ACT_EXT_SHIFT)
 #define TC_ACT_EXT_VAL_MASK ((1 << __TC_ACT_EXT_SHIFT) - 1)
-#define TC_ACT_EXT_CMP(combined, opcode) \
-	(((combined) & (~TC_ACT_EXT_VAL_MASK)) == opcode)
+#define TC_ACT_EXT_OPCODE(combined) ((combined) & (~TC_ACT_EXT_VAL_MASK))
+#define TC_ACT_EXT_CMP(combined, opcode) (TC_ACT_EXT_OPCODE(combined) == opcode)
 
 #define TC_ACT_JUMP __TC_ACT_EXT(1)
 #define TC_ACT_GOTO_CHAIN __TC_ACT_EXT(2)
+#define TC_ACT_EXT_OPCODE_MAX	TC_ACT_GOTO_CHAIN
 
 /* Action type identifiers*/
 enum {

net/sched/act_api.c

@@ -786,6 +786,15 @@ 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,
@@ -895,6 +904,11 @@ struct tc_action *tcf_action_init_1(struct net *net, struct tcf_proto *tp,
 		}
 	}
 
+	if (!tcf_action_valid(a->tcfa_action)) {
+		NL_SET_ERR_MSG(extack, "invalid action value, using TC_ACT_UNSPEC instead");
+		a->tcfa_action = TC_ACT_UNSPEC;
+	}
+
 	return a;
 
 err_mod: