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From 3be810287878138e5f72568d1ba1160b5bad22f8 Mon Sep 17 00:00:00 2001
From: "Daniel P. Berrange" <>
Date: Thu, 8 Feb 2018 17:50:32 +0100
Subject: [PATCH 18/27] ui: track how much decoded data we consumed when doing
 SASL encoding
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RH-Author: Daniel P. Berrange <>
Message-id: <>
Patchwork-id: 78951
O-Subject: [RHEL-7.5 qemu-kvm PATCH v1 18/27] ui: track how much decoded data we consumed when doing SASL encoding
Bugzilla: 1527405
RH-Acked-by: Laszlo Ersek <>
RH-Acked-by: Gerd Hoffmann <>
RH-Acked-by: Miroslav Rezanina <>

From: "Daniel P. Berrange" <>

When we encode data for writing with SASL, we encode the entire pending output
buffer. The subsequent write, however, may not be able to send the full encoded
data in one go though, particularly with a slow network. So we delay setting the
output buffer offset back to zero until all the SASL encoded data is sent.

Between encoding the data and completing sending of the SASL encoded data,
however, more data might have been placed on the pending output buffer. So it
is not valid to set offset back to zero. Instead we must keep track of how much
data we consumed during encoding and subtract only that amount.

With the current bug we would be throwing away some pending data without having
sent it at all. By sheer luck this did not previously cause any serious problem
because appending data to the send buffer is always an atomic action, so we
only ever throw away complete RFB protocol messages. In the case of frame buffer
updates we'd catch up fairly quickly, so no obvious problem was visible.

RHEL-7 note: context difference in the last argument to
vnc_client_io_error() due to downstream lacking commit 04d2529da27d
("ui: convert VNC server to use QIOChannelSocket", 2015-12-18).

Signed-off-by: Daniel P. Berrange <>
Reviewed-by: Darren Kenny <>
Reviewed-by: Marc-André Lureau <>
Signed-off-by: Gerd Hoffmann <>
(cherry picked from commit 8f61f1c5a6bc06438a1172efa80bc7606594fa07)
Signed-off-by: Miroslav Rezanina <>
 ui/vnc-auth-sasl.c | 3 ++-
 ui/vnc-auth-sasl.h | 1 +
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/ui/vnc-auth-sasl.c b/ui/vnc-auth-sasl.c
index f3ad75d..804b8e7 100644
--- a/ui/vnc-auth-sasl.c
+++ b/ui/vnc-auth-sasl.c
@@ -64,6 +64,7 @@ long vnc_client_write_sasl(VncState *vs)
         if (err != SASL_OK)
             return vnc_client_io_error(vs, -1, EIO);
+        vs->sasl.encodedRawLength = vs->output.offset;
         vs->sasl.encodedOffset = 0;
@@ -75,7 +76,7 @@ long vnc_client_write_sasl(VncState *vs)
     vs->sasl.encodedOffset += ret;
     if (vs->sasl.encodedOffset == vs->sasl.encodedLength) {
-        vs->output.offset = 0;
+        vs->output.offset -= vs->sasl.encodedRawLength;
         vs->sasl.encoded = NULL;
         vs->sasl.encodedOffset = vs->sasl.encodedLength = 0;
diff --git a/ui/vnc-auth-sasl.h b/ui/vnc-auth-sasl.h
index 8091d68..4ec6fb5 100644
--- a/ui/vnc-auth-sasl.h
+++ b/ui/vnc-auth-sasl.h
@@ -54,6 +54,7 @@ struct VncStateSASL {
     const uint8_t *encoded;
     unsigned int encodedLength;
+    unsigned int encodedRawLength;
     unsigned int encodedOffset;
     char *username;
     char *mechlist;