[PATCH net] net: sched: correct flower port blocking

[Jason Baron <jbaron@akamai.com>]

tc flower rules that are based on src or dst port blocking are sometimes
ineffective due to uninitialized stack data. __skb_flow_dissect() extracts
ports from the skb for tc flower to match against. However, the port
dissection is not done when when the FLOW_DIS_IS_FRAGMENT bit is set in
key_control->flags. All callers of __skb_flow_dissect(), zero-out the
key_control field except for fl_classify() as used by the flower
classifier. Thus, the FLOW_DIS_IS_FRAGMENT may be set on entry to
__skb_flow_dissect(), since key_control is allocated on the stack
and may not be initialized.

Since key_basic and key_control are present for all flow keys, let's
make sure they are initialized.

Fixes: 62230715fd24 ("flow_dissector: do not dissect l4 ports for fragments")
Co-developed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Jason Baron <jbaron@akamai.com>
---
 include/linux/skbuff.h | 8 ++++++++
 net/sched/cls_flower.c | 1 +
 2 files changed, 9 insertions(+)

diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index ca8806b..f953bfa 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1288,6 +1288,14 @@ bool __skb_flow_dissect(const struct net *net,
 			void *data, __be16 proto, int nhoff, int hlen,
 			unsigned int flags);
 
+static inline void
+skb_flow_dissect_init_key(struct flow_dissector_key_control *key_control,
+			  struct flow_dissector_key_basic *key_basic)
+{
+	memset(key_control, 0, sizeof(*key_control));
+	memset(key_basic, 0, sizeof(*key_basic));
+}
+
 static inline bool skb_flow_dissect(const struct sk_buff *skb,
 				    struct flow_dissector *flow_dissector,
 				    void *target_container, unsigned int flags)
diff --git a/net/sched/cls_flower.c b/net/sched/cls_flower.c
index f9c0d1e..b0a534b 100644
--- a/net/sched/cls_flower.c
+++ b/net/sched/cls_flower.c
@@ -305,6 +305,7 @@ static int fl_classify(struct sk_buff *skb, const struct tcf_proto *tp,
 	struct cls_fl_filter *f;
 
 	list_for_each_entry_rcu(mask, &head->masks, list) {
+		skb_flow_dissect_init_key(&skb_key.control, &skb_key.basic);
 		fl_clear_masked_range(&skb_key, mask);
 
 		skb_flow_dissect_meta(skb, &mask->dissector, &skb_key);
-- 
2.7.4