fib: fix load-balance and replicate dpos buckets overflow

load-balance and replicate dpos both store their number of buckets as
u16, which can overflow if too many paths are configured. For
load-balance it can happens quite quickly because of weights
normalization.

Type: fix

Change-Id: I0c78c39fc3d40626dfc58b49e7d99d71f9852b50
Signed-off-by: Benoît Ganne <bganne@cisco.com>

4 files changed, 53 insertions, 9 deletions

diff --git a/src/vnet/dpo/load_balance.c b/src/vnet/dpo/load_balance.c
index ff46d56e3e2..fae7c1db94a 100644
--- a/src/vnet/dpo/load_balance.c
+++ b/src/vnet/dpo/load_balance.c
@@ -244,6 +244,8 @@ load_balance_create_i (u32 num_buckets,
 {
     load_balance_t *lb;
 
+    ASSERT (num_buckets <= LB_MAX_BUCKETS);
+
     lb = load_balance_alloc_i();
     lb->lb_hash_config = fhc;
     lb->lb_n_buckets = num_buckets;
@@ -455,8 +457,9 @@ ip_multipath_normalize_next_hops (const load_balance_path_t * raw_next_hops,
 
     /* Try larger and larger power of 2 sized adjacency blocks until we
        find one where traffic flows to within 1% of specified weights. */
-    for (n_adj = max_pow2 (n_nhs); ; n_adj *= 2)
+    for (n_adj = clib_min(max_pow2 (n_nhs), LB_MAX_BUCKETS); ; n_adj *= 2)
     {
+        ASSERT (n_adj <= LB_MAX_BUCKETS);
         error = 0;
 
         norm = n_adj / ((f64) sum_weight);
@@ -487,12 +490,22 @@ ip_multipath_normalize_next_hops (const load_balance_path_t * raw_next_hops,
 
         nhs[0].path_weight += n_adj_left;
 
-        /* Less than 5% average error per adjacency with this size adjacency block? */
-        if (error <= multipath_next_hop_error_tolerance*n_adj)
+        /* Less than 1% average error per adjacency with this size adjacency block,
+         * or did we reached the maximum number of buckets we support? */
+        if (error <= multipath_next_hop_error_tolerance*n_adj ||
+            n_adj >= LB_MAX_BUCKETS)
         {
-            /* Truncate any next hops with zero weight. */
-            vec_set_len (nhs, i);
-            break;
+          if (i < n_nhs)
+          {
+            /* Truncate any next hops in excess */
+            vlib_log_err(load_balance_logger,
+                         "Too many paths for load-balance, truncating %d -> %d",
+                         n_nhs, i);
+            for (int j = i; j < n_nhs; j++)
+              dpo_reset (&vec_elt(nhs, j).path_dpo);
+          }
+          vec_set_len (nhs, i);
+          break;
         }
     }
 
@@ -622,6 +635,7 @@ static inline void
 load_balance_set_n_buckets (load_balance_t *lb,
                             u32 n_buckets)
 {
+    ASSERT (n_buckets <= LB_MAX_BUCKETS);
     lb->lb_n_buckets = n_buckets;
     lb->lb_n_buckets_minus_1 = n_buckets-1;
 }
@@ -651,8 +665,6 @@ load_balance_multipath_update (const dpo_id_t *dpo,
                                          &sum_of_weights,
                                          multipath_next_hop_error_tolerance);
 
-    ASSERT (n_buckets >= vec_len (raw_nhs));
-
     /*
      * Save the old load-balance map used, and get a new one if required.
      */
diff --git a/src/vnet/dpo/load_balance.h b/src/vnet/dpo/load_balance.h
index 5428e20e981..3605d82a207 100644
--- a/src/vnet/dpo/load_balance.h
+++ b/src/vnet/dpo/load_balance.h
@@ -50,6 +50,12 @@ typedef struct load_balance_main_t_
 extern load_balance_main_t load_balance_main;
 
 /**
+ * The maximum number of buckets that a load-balance object can have
+ * This must not overflow the lb_n_buckets field
+ */
+#define LB_MAX_BUCKETS 8192
+
+/**
  * The number of buckets that a load-balance object can have and still
  * fit in one cache-line
  */
@@ -176,6 +182,10 @@ typedef struct load_balance_t_ {
 
 STATIC_ASSERT(sizeof(load_balance_t) <= CLIB_CACHE_LINE_BYTES,
 	      "A load_balance object size exceeds one cacheline");
+STATIC_ASSERT (LB_MAX_BUCKETS <= CLIB_U16_MAX,
+	       "Too many buckets for load_balance object");
+STATIC_ASSERT (LB_MAX_BUCKETS && !(LB_MAX_BUCKETS & (LB_MAX_BUCKETS - 1)),
+	       "LB_MAX_BUCKETS must be a power of 2");
 
 /**
  * Flags controlling load-balance formatting/display
diff --git a/src/vnet/dpo/replicate_dpo.c b/src/vnet/dpo/replicate_dpo.c
index 5f88f12b910..0474fd82984 100644
--- a/src/vnet/dpo/replicate_dpo.c
+++ b/src/vnet/dpo/replicate_dpo.c
@@ -172,6 +172,8 @@ replicate_create_i (u32 num_buckets,
 {
     replicate_t *rep;
 
+    ASSERT (num_buckets <= REP_MAX_BUCKETS);
+
     rep = replicate_alloc_i();
     rep->rep_n_buckets = num_buckets;
     rep->rep_proto = rep_proto;
@@ -311,7 +313,8 @@ static inline void
 replicate_set_n_buckets (replicate_t *rep,
                          u32 n_buckets)
 {
-    rep->rep_n_buckets = n_buckets;
+  ASSERT (n_buckets <= REP_MAX_BUCKETS);
+  rep->rep_n_buckets = n_buckets;
 }
 
 void
@@ -331,6 +334,17 @@ replicate_multipath_update (const dpo_id_t *dpo,
                                              rep->rep_proto);
     n_buckets = vec_len(nhs);
 
+    if (n_buckets > REP_MAX_BUCKETS)
+      {
+	vlib_log_err (replicate_logger,
+		      "Too many paths for replicate, truncating %d -> %d",
+		      n_buckets, REP_MAX_BUCKETS);
+	for (int i = REP_MAX_BUCKETS; i < n_buckets; i++)
+	  dpo_reset (&vec_elt (nhs, i).path_dpo);
+	vec_set_len (nhs, REP_MAX_BUCKETS);
+	n_buckets = REP_MAX_BUCKETS;
+      }
+
     if (0 == rep->rep_n_buckets)
     {
         /*
diff --git a/src/vnet/dpo/replicate_dpo.h b/src/vnet/dpo/replicate_dpo.h
index 908c20c1d56..d21f52a4833 100644
--- a/src/vnet/dpo/replicate_dpo.h
+++ b/src/vnet/dpo/replicate_dpo.h
@@ -41,6 +41,12 @@ typedef struct replicate_main_t_
 extern replicate_main_t replicate_main;
 
 /**
+ * The number of buckets that a replicate object can have
+ * This must not overflow the rep_n_buckets field
+ */
+#define REP_MAX_BUCKETS 1024
+
+/**
  * The number of buckets that a load-balance object can have and still
  * fit in one cache-line
  */
@@ -108,6 +114,8 @@ typedef struct replicate_t_ {
 
 STATIC_ASSERT(sizeof(replicate_t) <= CLIB_CACHE_LINE_BYTES,
 	      "A replicate object size exceeds one cacheline");
+STATIC_ASSERT (REP_MAX_BUCKETS <= CLIB_U16_MAX,
+	       "Too many buckets for replicate object");
 
 /**
  * Flags controlling load-balance formatting/display