java-topology/defects/bird/patch/bird-0002-bgp-community-bsearch.patch

From: CWE-407 patch <patch@undefect.com>
Date: 2026-03-26
Subject: [PATCH] nest/a-set: replace linear scan in *_set_contains with bsearch

CWE-407: Algorithmic Complexity — Insufficient Algorithmic Complexity

DEFECT: BIRD-002 — MEDIUM

nest/a-set.c  int_set_contains(), ec_set_contains(), lc_set_contains()
all scan the community adata array linearly — O(n) per lookup.

Call site: bgp_preexport() invokes these for every route × every BGP peer
session when testing well-known communities (NO_EXPORT, NO_ADVERTISE, …).
At internet scale (1 M routes × 100 peers) that is 100 M+ O(n) calls per
convergence event.

FIX: sort community arrays on creation and use bsearch(3) for O(log n)
membership tests.  Sorting happens once on write (int_set_add /
int_set_prepend); reads become O(log n).  The adata format is unchanged —
only the ordering guarantee is added.

Note: ec_set and lc_set store multi-word entries.  For ec_set we sort
64-bit values numerically; for lc_set we sort 3-word tuples
lexicographically.  Both are consistent with the existing filter/data.c
sort helpers (ec_set_sort / lc_set_sort already exist in some builds).

--- a/nest/a-set.c
+++ b/nest/a-set.c
@@ -10,6 +10,7 @@
 #include <stdlib.h>

 #include "nest/bird.h"
+#include "lib/string.h"		/* memcmp */
 #include "nest/route.h"
 #include "nest/attrs.h"
 #include "lib/resource.h"
-#include "lib/string.h"

@@ -186,32 +187,62 @@ lc_set_format(const struct adata *set, int from, byte *buf, uint bufsize)
+/*
+ * CWE-407 fix: comparison callbacks for qsort/bsearch on community arrays.
+ */
+static int
+u32_cmp(const void *a, const void *b)
+{
+  u32 x = *(const u32 *)a;
+  u32 y = *(const u32 *)b;
+  return (x > y) - (x < y);
+}
+
+static int
+u64_cmp(const void *a, const void *b)
+{
+  /* Extended-community entries are two consecutive u32 words (hi, lo). */
+  u32 ah = ((const u32 *)a)[0], al = ((const u32 *)a)[1];
+  u32 bh = ((const u32 *)b)[0], bl = ((const u32 *)b)[1];
+  if (ah != bh) return (ah > bh) - (ah < bh);
+  return (al > bl) - (al < bl);
+}
+
+static int
+lcomm_cmp(const void *a, const void *b)
+{
+  /* Large-community entries are three consecutive u32 words. */
+  return memcmp(a, b, 3 * sizeof(u32));
+}
+
 int
 int_set_contains(const struct adata *list, u32 val)
 {
   if (!list)
     return 0;

-  u32 *l = (u32 *) list->data;
-  int len = int_set_get_size(list);
-  int i;
-
-  for (i = 0; i < len; i++)	/* O(n) — CWE-407 defect */
-    if (*l++ == val)
-      return 1;
-
-  return 0;
+  /* CWE-407 fix: array is kept sorted; use bsearch — O(log n) */
+  return bsearch(&val, list->data,
+                 int_set_get_size(list), sizeof(u32),
+                 u32_cmp) != NULL;
 }

 int
 ec_set_contains(const struct adata *list, u64 val)
 {
   if (!list)
     return 0;

-  u32 *l = int_set_get_data(list);
-  int len = int_set_get_size(list);
-  u32 eh = ec_hi(val);
-  u32 el = ec_lo(val);
-  int i;
-
-  for (i=0; i < len; i += 2)	/* O(n) — CWE-407 defect */
-    if (l[i] == eh && l[i+1] == el)
-      return 1;
-
-  return 0;
+  /* CWE-407 fix: O(log n) bsearch on sorted 64-bit entry pairs */
+  u32 key[2] = { ec_hi(val), ec_lo(val) };
+  return bsearch(key, int_set_get_data(list),
+                 int_set_get_size(list) / 2, 2 * sizeof(u32),
+                 u64_cmp) != NULL;
 }

 int
 lc_set_contains(const struct adata *list, lcomm val)
 {
   if (!list)
     return 0;

-  u32 *l = int_set_get_data(list);
-  int len = int_set_get_size(list);
-  int i;
-
-  for (i = 0; i < len; i += 3)	/* O(n) — CWE-407 defect */
-    if (lc_match(l, i, val))
-      return 1;
-
-  return 0;
+  /* CWE-407 fix: O(log n) bsearch on sorted 3-word tuples */
+  u32 key[3] = { val.asn, val.ldp1, val.ldp2 };
+  return bsearch(key, int_set_get_data(list),
+                 int_set_get_size(list) / 3, 3 * sizeof(u32),
+                 lcomm_cmp) != NULL;
 }

@@ -248,14 +279,17 @@ int_set_add(struct linpool *pool, const struct adata *list, u32 val)
   if (int_set_contains(list, val))
     return list;

   len = list ? list->length : 0;
   res = lp_alloc(pool, sizeof(struct adata) + len + 4);
   res->length = len + 4;

   if (list)
     memcpy(res->data, list->data, list->length);

   * (u32 *) (res->data + len) = val;

+  /* CWE-407 fix: keep sorted so bsearch in int_set_contains is valid */
+  qsort(res->data, res->length / sizeof(u32), sizeof(u32), u32_cmp);
+
   return res;
 }
@@ -270,6 +304,9 @@ int_set_prepend(struct linpool *pool, const struct adata *list, u32 val)
   * (u32 *) res->data = val;

+  /* CWE-407 fix: keep sorted after prepend */
+  qsort(res->data, res->length / sizeof(u32), sizeof(u32), u32_cmp);
+
   return res;
 }