io: monitor encoutput buffer size from websocket GSource

PATCH New Daniel P. Berrange 1 participant 1 message Oct 17, 2017

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Daniel P. Berrange

author

2017-10-17 14:37 UTC #0 lore raw

PATCH 1/1 io: monitor encoutput buffer size from websocket GSource

The websocket GSource is monitoring the size of the rawoutput buffer to determine if the channel can accepts more writes. The rawoutput buffer, however, is merely a temporary staging buffer before data is copied into the encoutput buffer. Thus its size will always be zero when the GSource runs.

This flaw causes the encoutput buffer to grow without bound if the other end of the underlying data channel doesn't read data being sent. This can be seen with VNC if a client is on a slow WAN link and the guest OS is sending many screen updates. A malicious VNC client can act like it is on a slow link by playing a video in the guest and then reading data very slowly, causing QEMU host memory to expand arbitrarily.

This issue is assigned CVE-2017-15268, publically reported in

https://bugs.launchpad.net/qemu/+bug/1718964

(cherry picked from commit a7b20a8efa28e5f22c26c06cd06c2f12bc863493)

Reviewed-by Eric Blake <[email protected]>

[Dan: Added extra checks to deal with code refactored in master but
not stable 2.10]

Signed-off-by Daniel P. Berrange <[email protected]>

---
 io/channel-websock.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

io/channel-websock.c +4 -4

index 5a3badbec2..19116dc148 100644
@@ -26,7 +26,7 @@
 #include "trace.h"
 
 
-/* Max amount to allow in rawinput/rawoutput buffers */
+/* Max amount to allow in rawinput/encoutput buffers */
 #define QIO_CHANNEL_WEBSOCK_MAX_BUFFER 8192
 
 #define QIO_CHANNEL_WEBSOCK_CLIENT_KEY_LEN 24

@@ -1006,7 +1006,7 @@ qio_channel_websock_source_prepare(GSource *source,
     if (wsource->wioc->rawinput.offset) {
         cond |= G_IO_IN;
     }
-    if (wsource->wioc->rawoutput.offset < QIO_CHANNEL_WEBSOCK_MAX_BUFFER) {
+    if (wsource->wioc->encoutput.offset < QIO_CHANNEL_WEBSOCK_MAX_BUFFER) {
         cond |= G_IO_OUT;
     }

@@ -1022,7 +1022,7 @@ qio_channel_websock_source_check(GSource *source)
     if (wsource->wioc->rawinput.offset) {
         cond |= G_IO_IN;
     }
-    if (wsource->wioc->rawoutput.offset < QIO_CHANNEL_WEBSOCK_MAX_BUFFER) {
+    if (wsource->wioc->encoutput.offset < QIO_CHANNEL_WEBSOCK_MAX_BUFFER) {
         cond |= G_IO_OUT;
     }

@@ -1041,7 +1041,7 @@ qio_channel_websock_source_dispatch(GSource *source,
     if (wsource->wioc->rawinput.offset) {
         cond |= G_IO_IN;
     }
-    if (wsource->wioc->rawoutput.offset < QIO_CHANNEL_WEBSOCK_MAX_BUFFER) {
+    if (wsource->wioc->encoutput.offset < QIO_CHANNEL_WEBSOCK_MAX_BUFFER) {
         cond |= G_IO_OUT;
     }

Signature · 1 line

2.13.6