From: Matt Corallo <git@bluematt.me>
Date: Sat, 15 Jun 2024 21:32:45 +0000 (+0000)
Subject: Prefer existing src buckets even if others timed out
X-Git-Url: http://git.bitcoin.ninja/?a=commitdiff_plain;h=3f743cd21690bb0452deff2e8eff52ed02df7cef;p=flowspec-xdp

Prefer existing src buckets even if others timed out

If we have some timed-out buckets in a source-based ratelimit,
we'll use those even if a later bucket is already storing the
counter for the source of the current packet. This is obviously
busted, so don't do that.
---

diff --git a/xdp.c b/xdp.c
index 187c220..4eea3e4 100644
--- a/xdp.c
+++ b/xdp.c
@@ -273,24 +273,26 @@ static int check_v##IPV##_persrc_ratelimit(IP_TYPE key, void *map, size_t map_li
 	struct persrc_rate##IPV##_entry *first_bucket = &buckets->entries[(hash % map_limit) & (~(SRC_HASH_BUCKET_COUNT - 1))]; \
 	bpf_spin_lock(&buckets->lock); \
  \
-	uint64_t min_sent_idx = 0; /* Must be uint64_t or BPF verifier gets lost and thinks it can be any value */ \
+	uint64_t bucket_idx = SRC_HASH_BUCKET_COUNT; \
+	uint64_t min_sent_idx = 0; \
 	uint64_t min_sent_time = UINT64_MAX; \
 	for (uint64_t i = 0; i < SRC_HASH_BUCKET_COUNT; i++) { \
 		if (first_bucket[i].srcip == key) { \
-			min_sent_idx = i; \
+			bucket_idx = i; \
 			break; \
 		} \
 		int64_t time_offset = ((int64_t)cur_time_masked) - (first_bucket[i].sent_time & RATE_TIME_MASK); \
 		if (time_offset < RATE_MIN_TIME_OFFSET || time_offset > RATE_MAX_TIME_OFFSET) { \
+			min_sent_time = 0; \
 			min_sent_idx = i; \
-			break; \
 		} \
 		if ((first_bucket[i].sent_time & RATE_TIME_MASK) < min_sent_time) { \
 			min_sent_time = first_bucket[i].sent_time & RATE_TIME_MASK; \
 			min_sent_idx = i; \
 		} \
 	} \
-	struct persrc_rate##IPV##_entry *entry = &first_bucket[min_sent_idx]; \
+	if (bucket_idx >= SRC_HASH_BUCKET_COUNT) bucket_idx = min_sent_idx; \
+	struct persrc_rate##IPV##_entry *entry = &first_bucket[bucket_idx]; \
 	if (entry->srcip != key) { \
 		entry->srcip = key; \
 		entry->sent_time = 0; \