nx-match: Succeed pulling 0-byte nx-match from NULL buffer.

I don't think this corner case can come up in a real OpenFlow message,
because the presence of the OpenFlow header guarantees that the ofpbuf's
data is nonnull, but it did in a simple test that is coming up in a few
commits.

Signed-off-by: Ben Pfaff <blp@nicira.com>

diff --git a/lib/nx-match.c b/lib/nx-match.c
index 3e3b4c69b1b3d547cd7b5739d55398d71f095554..8b2a82292e9e37eab5c9fc7a46ef39f6a877c7f4 100644 (file)
--- a/lib/nx-match.c
+++ b/lib/nx-match.c
@@ -99,6 +99,14 @@ nx_pull_match__(struct ofpbuf *b, unsigned int match_len, bool strict,
 
     assert((cookie != NULL) == (cookie_mask != NULL));
 
+    cls_rule_init_catchall(rule, priority);
+    if (cookie) {
+        *cookie = *cookie_mask = htonll(0);
+    }
+    if (!match_len) {
+        return 0;
+    }
+
     p = ofpbuf_try_pull(b, ROUND_UP(match_len, 8));
     if (!p) {
         VLOG_DBG_RL(&rl, "nx_match length %u, rounded up to a "
@@ -107,10 +115,6 @@ nx_pull_match__(struct ofpbuf *b, unsigned int match_len, bool strict,
         return OFPERR_OFPBMC_BAD_LEN;
     }
 
-    cls_rule_init_catchall(rule, priority);
-    if (cookie) {
-        *cookie = *cookie_mask = htonll(0);
-    }
     for (;
          (header = nx_entry_ok(p, match_len)) != 0;
          p += 4 + NXM_LENGTH(header), match_len -= 4 + NXM_LENGTH(header)) {