Re: [Qemu-devel] [PATCH v2 6/6] io: Reply to ping frames

[Brandon Carpenter <brandon.carpenter@cypherpath.com>]

On Mon, Sep 11, 2017 at 1:50 AM, Daniel P. Berrange 
<berrange@redhat.com> wrote:
> I'm concerned that there is no rate limiting here though, so if a 
> large number of PINGs are sent, and writing of the reply blocks for 
> some reason, encoutput will grow without bounds.

That is a good point. How about something like this to fix it?

diff --git a/include/io/channel-websock.h b/include/io/channel-websock.h
index 7c896557c5..c5a8c3e96c 100644
--- a/include/io/channel-websock.h
+++ b/include/io/channel-websock.h
@@ -66,6 +66,7 @@ struct QIOChannelWebsock {
     Error *io_err;
     gboolean io_eof;
     uint8_t opcode;
+ uint8_t prev_opcode;
 };

 /**
diff --git a/io/channel-websock.c b/io/channel-websock.c
index 175f17ce6b..a9315c01fb 100644
--- a/io/channel-websock.c
+++ b/io/channel-websock.c
@@ -549,6 +549,7 @@ static int 
qio_channel_websock_decode_header(QIOChannelWebsock *ioc,
     payload_len = header->b1 & 
QIO_CHANNEL_WEBSOCK_HEADER_FIELD_PAYLOAD_LEN;

     /* Save or restore opcode. */
+ ioc->prev_opcode = ioc->opcode;
     if (opcode) {
         ioc->opcode = opcode;
     } else {
@@ -658,9 +659,14 @@ static int 
qio_channel_websock_decode_payload(QIOChannelWebsock *ioc,
             buffer_append(&ioc->rawinput, ioc->encinput.buffer, 
payload_len);
         }
     } else if (ioc->opcode == QIO_CHANNEL_WEBSOCK_OPCODE_PING) {
- /* ping frames produce an immediate pong reply */
- qio_channel_websock_encode_buffer(ioc,
- QIO_CHANNEL_WEBSOCK_OPCODE_PONG, &ioc->encinput);
+ /* Ping frames produce an immediate pong reply, unless one
+ * is already queued, in which case they are coalesced
+ * to avoid unbounded buffer growth.
+ */
+ if (!ioc->encoutput.offset || ioc->prev_opcode != 
QIO_CHANNEL_WEBSOCK_OPCODE_PING) {
+ qio_channel_websock_encode_buffer(ioc,
+ QIO_CHANNEL_WEBSOCK_OPCODE_PONG, &ioc->encinput);
+ }
     } /* pong frames are ignored */

     if (payload_len) {

--
Brandon Carpenter | Software Engineer
Cypherpath, Inc.
400 Columbia Point Drive Ste 101 | Richland, Washington USA
Office: (650) 713-3060


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