Merge branch 'cls_u32-fix-refcount-leak'

Davide Caratti says:

====================
net/sched: cls_u32: fix refcount leak

a refcount leak in the error path of u32_change() has been recently
introduced. It can be observed with the following commands:

  [root@f31 ~]# tc filter replace dev eth0 ingress protocol ip prio 97 \
  > u32 match ip src 127.0.0.1/32 indev notexist20 flowid 1:1 action drop
  RTNETLINK answers: Invalid argument
  We have an error talking to the kernel
  [root@f31 ~]# tc filter replace dev eth0 ingress protocol ip prio 98 \
  > handle 42:42 u32 divisor 256
  Error: cls_u32: Divisor can only be used on a hash table.
  We have an error talking to the kernel
  [root@f31 ~]# tc filter replace dev eth0 ingress protocol ip prio 99 \
  > u32 ht 47:47
  Error: cls_u32: Specified hash table not found.
  We have an error talking to the kernel

they all legitimately return -EINVAL; however, they leave semi-configured
filters at eth0 tc ingress:

 [root@f31 ~]# tc filter show dev eth0 ingress
 filter protocol ip pref 97 u32 chain 0
 filter protocol ip pref 97 u32 chain 0 fh 800: ht divisor 1
 filter protocol ip pref 98 u32 chain 0
 filter protocol ip pref 98 u32 chain 0 fh 801: ht divisor 1
 filter protocol ip pref 99 u32 chain 0
 filter protocol ip pref 99 u32 chain 0 fh 802: ht divisor 1

With older kernels, filters were unconditionally considered empty (and
thus de-refcounted) on the error path of ->change().
After commit 8b64678e0af8 ("net: sched: refactor tp insert/delete for
concurrent execution"), filters were considered empty when the walk()
function didn't set 'walker.stop' to 1.
Finally, with commit 6676d5e416ee ("net: sched: set dedicated tcf_walker
flag when tp is empty"), tc filters are considered empty unless the walker
function is called with a non-NULL handle. This last change doesn't fit
cls_u32 design, because at least the "root hnode" is (almost) always
non-NULL, as it's allocated in u32_init().

- patch 1/2 is a proposal to restore the original kernel behavior, where
  no filter was installed in the error path of u32_change().
- patch 2/2 adds tdc selftests that can be ued to verify the correct
  behavior of u32 in the error path of ->change().
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 25 insertions, 0 deletions

diff --git a/net/sched/cls_u32.c b/net/sched/cls_u32.c
index a0e6fac613de..66c6bcec16cb 100644
--- a/net/sched/cls_u32.c
+++ b/net/sched/cls_u32.c
@@ -1108,10 +1108,33 @@ erridr:
 	return err;
 }
 
+static bool u32_hnode_empty(struct tc_u_hnode *ht, bool *non_root_ht)
+{
+	int i;
+
+	if (!ht)
+		return true;
+	if (!ht->is_root) {
+		*non_root_ht = true;
+		return false;
+	}
+	if (*non_root_ht)
+		return false;
+	if (ht->refcnt < 2)
+		return true;
+
+	for (i = 0; i <= ht->divisor; i++) {
+		if (rtnl_dereference(ht->ht[i]))
+			return false;
+	}
+	return true;
+}
+
 static void u32_walk(struct tcf_proto *tp, struct tcf_walker *arg,
 		     bool rtnl_held)
 {
 	struct tc_u_common *tp_c = tp->data;
+	bool non_root_ht = false;
 	struct tc_u_hnode *ht;
 	struct tc_u_knode *n;
 	unsigned int h;
@@ -1124,6 +1147,8 @@ static void u32_walk(struct tcf_proto *tp, struct tcf_walker *arg,
 	     ht = rtnl_dereference(ht->next)) {
 		if (ht->prio != tp->prio)
 			continue;
+		if (u32_hnode_empty(ht, &non_root_ht))
+			return;
 		if (arg->count >= arg->skip) {
 			if (arg->fn(tp, ht, arg) < 0) {
 				arg->stop = 1;