[tor-commits] [tor/master] Use uint32 !=, not tor_memneq, for relay cell integrity checking

[nickm at torproject.org]

commit d9564d528514442e73221d8fbc3044856a2010a9
Author: Nick Mathewson <nickm at torproject.org>
Date:   Sun Jun 1 14:02:55 2014 -0400

    Use uint32 !=, not tor_memneq, for relay cell integrity checking
    
    tor_memeq has started to show up on profiles, and this is one of the
    most frequent callers of that function, appearing as it does on every
    cell handled for entry or exit.
    
    59f9097d5c3dc010847c359888d31757d1c97904 introduced tor_memneq here;
    it went into Tor 0.2.1.31.  Fixes part of 12169.
---
 changes/bug12169_simple |    5 +++++
 src/or/relay.c          |   10 +++++-----
 2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/changes/bug12169_simple b/changes/bug12169_simple
new file mode 100644
index 0000000..f9a3007
--- /dev/null
+++ b/changes/bug12169_simple
@@ -0,0 +1,5 @@
+  o Minor bugfixes (performance):
+    - Avoid using tor_memeq() for checking relay cell integrity.
+      This removes a possible performance bottleneck. Fixes part of bug
+      12169; bugfix on 0.2.1.31.
+
diff --git a/src/or/relay.c b/src/or/relay.c
index 5c430a6..509d7ce 100644
--- a/src/or/relay.c
+++ b/src/or/relay.c
@@ -111,14 +111,14 @@ relay_set_digest(crypto_digest_t *digest, cell_t *cell)
 static int
 relay_digest_matches(crypto_digest_t *digest, cell_t *cell)
 {
-  char received_integrity[4], calculated_integrity[4];
+  uint32_t received_integrity, calculated_integrity;
   relay_header_t rh;
   crypto_digest_t *backup_digest=NULL;
 
   backup_digest = crypto_digest_dup(digest);
 
   relay_header_unpack(&rh, cell->payload);
-  memcpy(received_integrity, rh.integrity, 4);
+  memcpy(&received_integrity, rh.integrity, 4);
   memset(rh.integrity, 0, 4);
   relay_header_pack(cell->payload, &rh);
 
@@ -127,15 +127,15 @@ relay_digest_matches(crypto_digest_t *digest, cell_t *cell)
 //    received_integrity[2], received_integrity[3]);
 
   crypto_digest_add_bytes(digest, (char*) cell->payload, CELL_PAYLOAD_SIZE);
-  crypto_digest_get_digest(digest, calculated_integrity, 4);
+  crypto_digest_get_digest(digest, (char*) &calculated_integrity, 4);
 
-  if (tor_memneq(received_integrity, calculated_integrity, 4)) {
+  if (calculated_integrity != received_integrity) {
 //    log_fn(LOG_INFO,"Recognized=0 but bad digest. Not recognizing.");
 // (%d vs %d).", received_integrity, calculated_integrity);
     /* restore digest to its old form */
     crypto_digest_assign(digest, backup_digest);
     /* restore the relay header */
-    memcpy(rh.integrity, received_integrity, 4);
+    memcpy(rh.integrity, &received_integrity, 4);
     relay_header_pack(cell->payload, &rh);
     crypto_digest_free(backup_digest);
     return 0;