netlink: fix policy dump leak

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

Fixes: d07dcf9a ("netlink: add infrastructure to expose policies to userspace")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/netlink.h

@@ -1934,7 +1934,8 @@ void nla_get_range_signed(const struct nla_policy *pt,
 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

@@ -1079,7 +1079,7 @@ static int ctrl_dumppolicy(struct sk_buff *skb, struct netlink_callback *cb)
 	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;
 
@@ -1113,6 +1113,12 @@ static int ctrl_dumppolicy(struct sk_buff *skb, struct netlink_callback *cb)
 	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,
@@ -1123,6 +1129,7 @@ static const struct genl_ops genl_ctrl_ops[] = {
 	{
 		.cmd		= CTRL_CMD_GETPOLICY,
 		.dumpit		= ctrl_dumppolicy,
+		.done		= ctrl_dumppolicy_done,
 	},
 };
 

net/netlink/policy.c

@@ -84,7 +84,6 @@ int netlink_policy_dump_start(const struct nla_policy *policy,
 	unsigned int policy_idx;
 	int err;
 
-	/* also returns 0 if "*_state" is our ERR_PTR() end marker */
 	if (*_state)
 		return 0;
 
@@ -140,21 +139,11 @@ static bool netlink_policy_dump_finished(struct nl_policy_dump *state)
 	       !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;
-
-	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;
-	}
+	struct nl_policy_dump *state = (void *)_state;
 
-	return true;
+	return !netlink_policy_dump_finished(state);
 }
 
 int netlink_policy_dump_write(struct sk_buff *skb, unsigned long _state)
@@ -309,3 +298,10 @@ int netlink_policy_dump_write(struct sk_buff *skb, unsigned long _state)
 	nla_nest_cancel(skb, policy);
 	return -ENOBUFS;
 }
+
+void netlink_policy_dump_free(unsigned long _state)
+{
+	struct nl_policy_dump *state = (void *)_state;
+
+	kfree(state);
+}