From 2b5a03a88c4e74bca1065072397c756836811378 Mon Sep 17 00:00:00 2001
From: Mike Gelfand <mikedld@mikedld.com>
Date: Wed, 24 Jun 2015 21:24:41 +0000
Subject: [PATCH] #5964: Another follow-up commit for #5456 (encrypted
 communication with libevent 2.1.x)

Decrypt only what is asked for, not more. This fixes previous commit
which changed semantics by processing the buffer to the very end,
starting with correct offset though.

Refactor encryption/decryption to a single function which callback.
---
 libtransmission/peer-io.c | 70 +++++++++++++++++++++++++--------------
 1 file changed, 45 insertions(+), 25 deletions(-)

diff --git a/libtransmission/peer-io.c b/libtransmission/peer-io.c
index 98f806624..79cb0f8c2 100644
--- a/libtransmission/peer-io.c
+++ b/libtransmission/peer-io.c
@@ -1041,6 +1041,33 @@ tr_peerIoSetEncryption (tr_peerIo * io, tr_encryption_type encryption_type)
 ***
 **/
 
+static inline void
+processBuffer (tr_crypto        * crypto,
+               struct evbuffer  * buffer,
+               size_t             offset,
+               size_t             size,
+               void            (* callback) (tr_crypto *, size_t, const void *, void *))
+{
+    struct evbuffer_ptr pos;
+    struct evbuffer_iovec iovec;
+
+    evbuffer_ptr_set (buffer, &pos, offset, EVBUFFER_PTR_SET);
+
+    do
+    {
+        if (evbuffer_peek (buffer, size, &pos, &iovec, 1) <= 0)
+            break;
+
+        callback (crypto, iovec.iov_len, iovec.iov_base, iovec.iov_base);
+
+        assert (size >= iovec.iov_len);
+        size -= iovec.iov_len;
+    }
+    while (!evbuffer_ptr_set (buffer, &pos, iovec.iov_len, EVBUFFER_PTR_ADD));
+
+    assert (size == 0);
+}
+
 static void
 addDatatype (tr_peerIo * io, size_t byteCount, bool isPieceData)
 {
@@ -1051,27 +1078,21 @@ addDatatype (tr_peerIo * io, size_t byteCount, bool isPieceData)
     peer_io_push_datatype (io, d);
 }
 
-static void
-maybeEncryptBuffer (tr_peerIo * io, struct evbuffer * buf)
+static inline void
+maybeEncryptBuffer (tr_peerIo       * io,
+                    struct evbuffer * buf,
+                    size_t            offset,
+                    size_t            size)
 {
     if (io->encryption_type == PEER_ENCRYPTION_RC4)
-    {
-        struct evbuffer_ptr pos;
-        struct evbuffer_iovec iovec;
-        evbuffer_ptr_set (buf, &pos, 0, EVBUFFER_PTR_SET);
-        do {
-            if (evbuffer_peek (buf, -1, &pos, &iovec, 1) != 1)
-              break;
-            tr_cryptoEncrypt (&io->crypto, iovec.iov_len, iovec.iov_base, iovec.iov_base);
-        } while (!evbuffer_ptr_set (buf, &pos, iovec.iov_len, EVBUFFER_PTR_ADD));
-    }
+        processBuffer (&io->crypto, buf, offset, size, &tr_cryptoEncrypt);
 }
 
 void
 tr_peerIoWriteBuf (tr_peerIo * io, struct evbuffer * buf, bool isPieceData)
 {
     const size_t byteCount = evbuffer_get_length (buf);
-    maybeEncryptBuffer (io, buf);
+    maybeEncryptBuffer (io, buf, 0, byteCount);
     evbuffer_add_buffer (io->outbuf, buf);
     addDatatype (io, byteCount, isPieceData);
 }
@@ -1127,6 +1148,16 @@ evbuffer_add_uint64 (struct evbuffer * outbuf, uint64_t addme_hll)
 ****
 ***/
 
+static inline void
+maybeDecryptBuffer (tr_peerIo       * io,
+                    struct evbuffer * buf,
+                    size_t            offset,
+                    size_t            size)
+{
+    if (io->encryption_type == PEER_ENCRYPTION_RC4)
+        processBuffer (&io->crypto, buf, offset, size, &tr_cryptoDecrypt);
+}
+
 void
 tr_peerIoReadBytesToBuf (tr_peerIo * io, struct evbuffer * inbuf, struct evbuffer * outbuf, size_t byteCount)
 {
@@ -1142,18 +1173,7 @@ tr_peerIoReadBytesToBuf (tr_peerIo * io, struct evbuffer * inbuf, struct evbuffe
     evbuffer_add_buffer (outbuf, tmp);
     evbuffer_free (tmp);
 
-    /* decrypt if needed */
-    if (io->encryption_type == PEER_ENCRYPTION_RC4) {
-        struct evbuffer_ptr pos;
-        struct evbuffer_iovec iovec;
-        evbuffer_ptr_set (outbuf, &pos, old_length, EVBUFFER_PTR_SET);
-        do {
-            if (evbuffer_peek (outbuf, -1, &pos, &iovec, 1) != 1)
-              break;
-            tr_cryptoDecrypt (&io->crypto, iovec.iov_len, iovec.iov_base, iovec.iov_base);
-            byteCount -= iovec.iov_len;
-        } while (!evbuffer_ptr_set (outbuf, &pos, iovec.iov_len, EVBUFFER_PTR_ADD));
-    }
+    maybeDecryptBuffer (io, outbuf, old_length, byteCount);
 }
 
 void