[Qemu-devel] [PATCH 1/4] ui: avoid risk of 32-bit int overflow in VNC buffer check

["Daniel P. Berrangé" <berrange@redhat.com>]

For very large framebuffers, it is theoretically possible for the result
of 'vs->throttle_output_offset * VNC_THROTTLE_OUTPUT_LIMIT_SCALE' to
exceed the size of a 32-bit int. For this to happen in practice, the
video RAM would have to be set to a large enough value, which is not
likely today. None the less we can be paranoid against future growth by
using division instead of multiplication when checking the limits.

Reported-by: Laszlo Ersek <lersek@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
---
 ui/vnc.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/ui/vnc.c b/ui/vnc.c
index 93731accb6..e14e524764 100644
--- a/ui/vnc.c
+++ b/ui/vnc.c
@@ -1572,8 +1572,8 @@ void vnc_write(VncState *vs, const void *data, size_t len)
      * handshake, or from the job thread's VncState clone
      */
     if (vs->throttle_output_offset != 0 &&
-        vs->output.offset > (vs->throttle_output_offset *
-                             VNC_THROTTLE_OUTPUT_LIMIT_SCALE)) {
+        (vs->output.offset / VNC_THROTTLE_OUTPUT_LIMIT_SCALE) >
+        vs->throttle_output_offset) {
         trace_vnc_client_output_limit(vs, vs->ioc, vs->output.offset,
                                       vs->throttle_output_offset);
         vnc_disconnect_start(vs);
-- 
2.14.3