Expanding asn path buffer

Based on:
   [bgpd] AS4 bugfix by Chris Caputo <ccaputo@alt.net>

    * bgpd/bgp_aspath.c: (aspath_make_str_count) "assert (len < str_size)" was
      getting hit under certain 4-byte ASN conditions. New realloc strategy.

1 files changed, 27 insertions, 53 deletions

diff --git a/bgpd/bgp_aspath.c b/bgpd/bgp_aspath.c
index 242bd8ee..d6fa6af5 100644
--- a/bgpd/bgp_aspath.c
+++ b/bgpd/bgp_aspath.c
@@ -389,25 +389,6 @@ aspath_delimiter_char (u_char type, u_char which)
   return ' ';
 }
 
-/* countup asns from this segment and index onward */
-static int
-assegment_count_asns (struct assegment *seg, int from)
-{
-  int count = 0;
-  while (seg)
-    {
-      if (!from)
-        count += seg->length;
-      else
-        {
-          count += (seg->length - from);
-          from = 0;
-        }
-      seg = seg->next;
-    }
-  return count;
-}
-
 unsigned int
 aspath_count_confeds (struct aspath *aspath)
 {
@@ -517,12 +498,26 @@ aspath_count_numas (struct aspath *aspath)
   return num;
 }
 
+/* Expand aspath string */
+static char *
+aspath_expand (char *buf, size_t *size, size_t len, size_t growth)
+{
+  len += growth + 1;	/* space for null terminator */
+  if (len <= *size)
+    return buf;
+
+  while (len > *size)
+    *size += *size / 2;
+
+  return XREALLOC(MTYPE_AS_STR, buf, *size);
+}
+
 /* Convert aspath structure to string expression. */
 static char *
 aspath_make_str_count (struct aspath *as)
 {
   struct assegment *seg;
-  int str_size;
+  size_t str_size;
   int len = 0;
   char *str_buf;
 
@@ -536,18 +531,7 @@ aspath_make_str_count (struct aspath *as)
   
   seg = as->segments;
   
-  /* ASN takes 5 chars at least, plus seperator, see below.
-   * If there is one differing segment type, we need an additional
-   * 2 chars for segment delimiters, and the final '\0'.
-   * Hopefully this is large enough to avoid hitting the realloc
-   * code below for most common sequences.
-   *
-   * With 32bit ASNs, this range will increase, but only worth changing
-   * once there are significant numbers of ASN >= 100000
-   */
-#define ASN_STR_LEN (5 + 1)
-  str_size = MAX (assegment_count_asns (seg, 0) * ASN_STR_LEN + 2 + 1,
-                  ASPATH_STR_DEFAULT_LEN);
+  str_size = ASPATH_STR_DEFAULT_LEN;
   str_buf = XMALLOC (MTYPE_AS_STR, str_size);
 
   while (seg)
@@ -571,32 +555,22 @@ aspath_make_str_count (struct aspath *as)
             return NULL;
         }
       
-      /* We might need to increase str_buf, particularly if path has
-       * differing segments types, our initial guesstimate above will
-       * have been wrong.  need 5 chars for ASN, a seperator each and
-       * potentially two segment delimiters, plus a space between each
-       * segment and trailing zero.
-       *
-       * This may need to revised if/when significant numbers of
-       * ASNs >= 100000 are assigned and in-use on the internet...
-       */
-#define SEGMENT_STR_LEN(X) (((X)->length * ASN_STR_LEN) + 2 + 1 + 1)
-      if ( (len + SEGMENT_STR_LEN(seg)) > str_size)
-        {
-          str_size = len + SEGMENT_STR_LEN(seg);
-          str_buf = XREALLOC (MTYPE_AS_STR, str_buf, str_size);
-        }
-#undef ASN_STR_LEN
-#undef SEGMENT_STR_LEN
-      
       if (seg->type != AS_SEQUENCE)
-        len += snprintf (str_buf + len, str_size - len, 
-			 "%c", 
-                         aspath_delimiter_char (seg->type, AS_SEG_START));
+	{
+	  str_buf = aspath_expand(str_buf, &str_size, len, 1);
+	  len += snprintf (str_buf + len, str_size - len, 
+			   "%c", 
+			   aspath_delimiter_char (seg->type, AS_SEG_START));
+	}
       
       /* write out the ASNs, with their seperators, bar the last one*/
       for (i = 0; i < seg->length; i++)
         {
+#define APPROX_DIG_CNT(x) (x < 100000U ? 5 : 10)
+	  /* %u + %c + %c + " " (last two are below loop) */
+	  str_buf = aspath_expand(str_buf, &str_size, len,
+				  APPROX_DIG_CNT(seg->as[i]) + 3);
+
           len += snprintf (str_buf + len, str_size - len, "%u", seg->as[i]);
           
           if (i < (seg->length - 1))