netlink: fix policy dump leak

[ Upstream commit a95bc734e60449e7b073ff7ff70c35083b290ae9 ]

If userspace doesn't complete the policy dump, we leak the
allocated state. Fix this.

Fixes: d07dcf9aadd6 ("netlink: add infrastructure to expose policies to userspace")
Signed-off-by: Johannes Berg <[e-mail]>
Reviewed-by: Jakub Kicinski <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/net/netlink.h

···
 int netlink_policy_dump_start(const struct nla_policy *policy,
 			      unsigned int maxtype,
 			      unsigned long *state);
-bool netlink_policy_dump_loop(unsigned long *state);
+bool netlink_policy_dump_loop(unsigned long state);
 int netlink_policy_dump_write(struct sk_buff *skb, unsigned long state);
+void netlink_policy_dump_free(unsigned long state);
 
 #endif

net/netlink/genetlink.c

···
 	if (err)
 		return err;
 
-	while (netlink_policy_dump_loop(&cb->args[1])) {
+	while (netlink_policy_dump_loop(cb->args[1])) {
 		void *hdr;
 		struct nlattr *nest;
 
···
 	return skb->len;
 }
 
+static int ctrl_dumppolicy_done(struct netlink_callback *cb)
+{
+	netlink_policy_dump_free(cb->args[1]);
+	return 0;
+}
+
 static const struct genl_ops genl_ctrl_ops[] = {
 	{
 		.cmd		= CTRL_CMD_GETFAMILY,
···
 	{
 		.cmd		= CTRL_CMD_GETPOLICY,
 		.dumpit		= ctrl_dumppolicy,
+		.done		= ctrl_dumppolicy_done,
 	},
 };
 

net/netlink/policy.c

···
 	unsigned int policy_idx;
 	int err;
 
-	/* also returns 0 if "*_state" is our ERR_PTR() end marker */
 	if (*_state)
 		return 0;
 
···
 	       !state->policies[state->policy_idx].policy;
 }
 
-bool netlink_policy_dump_loop(unsigned long *_state)
+bool netlink_policy_dump_loop(unsigned long _state)
 {
-	struct nl_policy_dump *state = (void *)*_state;
+	struct nl_policy_dump *state = (void *)_state;
 
-	if (IS_ERR(state))
-		return false;
-
-	if (netlink_policy_dump_finished(state)) {
-		kfree(state);
-		/* store end marker instead of freed state */
-		*_state = (unsigned long)ERR_PTR(-ENOENT);
-		return false;
-	}
-
-	return true;
+	return !netlink_policy_dump_finished(state);
 }
 
 int netlink_policy_dump_write(struct sk_buff *skb, unsigned long _state)
···
 nla_put_failure:
 	nla_nest_cancel(skb, policy);
 	return -ENOBUFS;
+}
+
+void netlink_policy_dump_free(unsigned long _state)
+{
+	struct nl_policy_dump *state = (void *)_state;
+
+	kfree(state);
 }