net: Precede each CBC encrypted application data record with an empty one.

net/third_party/nss/patches/cbcrandomiv.patch

+commit 36840201a321147d9c33a944784ff56980aae5d8
+Author: Adam Langley <agl@chromium.org>
+Date:   Wed Jun 22 13:36:50 2011 -0400
+
+    cbcrandomiv.patch
+
+diff --git a/mozilla/security/nss/lib/ssl/ssl3con.c b/mozilla/security/nss/lib/ssl/ssl3con.c
+index 2cc1e05..eb7d63e 100644
+--- a/mozilla/security/nss/lib/ssl/ssl3con.c
++++ b/mozilla/security/nss/lib/ssl/ssl3con.c
+@@ -2229,7 +2229,7 @@ ssl3_SendRecord(   sslSocket *        ss,
+        return SECFailure;
+     }
+ 
+-    while (nIn > 0) {
++    do {
+        PRUint32  contentLen = PR_MIN(nIn, MAX_FRAGMENT_LENGTH);
+ 
+        if (wrBuf->space < contentLen + SSL3_BUFFER_FUDGE) {
+@@ -2306,7 +2306,7 @@ ssl3_SendRecord(   sslSocket *        ss,
+            }
+        }
+        totalSent += contentLen;
+-    }
++    } while (nIn > 0);
+     return totalSent;
+ }
+ 
+@@ -2321,6 +2321,7 @@ ssl3_SendApplicationData(sslSocket *ss, const unsigned char *in,
+ {
+     PRInt32   totalSent        = 0;
+     PRInt32   discarded = 0;
++    PRBool    isBlockCipher;
+ 
+     PORT_Assert( ss->opt.noLocks || ssl_HaveXmitBufLock(ss) );
+     if (len < 0 || !in) {
+@@ -2345,6 +2346,28 @@ ssl3_SendApplicationData(sslSocket *ss, const unsigned char *in,
+        len--;
+        discarded = 1;
+     }
++
++    ssl_GetSpecReadLock(ss);
++    isBlockCipher = ss->ssl3.cwSpec->cipher_def->type == type_block;
++    ssl_ReleaseSpecReadLock(ss);
++
++    if (isBlockCipher && len > 0) {
++       // We assume that block ciphers are used in CBC mode and prepend an
++       // empty record. This effectively randomizes the IV in a backwards
++       // compatible way.
++       PRInt32 sent = ssl3_SendRecord(ss, content_application_data,
++                                      in, 0 /* no payload */, flags);
++       if (sent < 0) {
++           return SECFailure; /* error code set by ssl3_SendRecord */
++       }
++       if (ss->pendingBuf.len) {
++           /* must be a non-blocking socket */
++           PORT_Assert(!ssl_SocketIsBlocking(ss));
++           PORT_Assert(ss->lastWriteBlocked);
++           return SECFailure;
++       }
++    }
++
+     while (len > totalSent) {
+        PRInt32   sent, toSend;
+ 
+@@ -2377,6 +2400,7 @@ ssl3_SendApplicationData(sslSocket *ss, const unsigned char *in,
+            break;      
+        }
+     }
++
+     if (ss->pendingBuf.len) {
+        /* Must be non-blocking. */
+        PORT_Assert(!ssl_SocketIsBlocking(ss));