[Qemu-devel] [Bug 1815371] [NEW] SPICE session's connection_id's are not unique

[Laurent Bigonville]

Public bug reported:

From: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=920897

=====

When creating a virtual machine with qemu (e.g. via libvirt) including a
SPICE server, the client_id of the SPICE session is not unique. For
example, starting multiple virtual machines on the same libvirtd, the
client_id is the same for all virtual machine's SPICE sessions.


A description of the client_id can be found in

https://www.spice-space.org/static/docs/spice_protocol.pdf under section
2.11. c) :


"UINT32 connection_id - In case of a new session (i.e., channel type is 
RED_CHANNEL_MAIN) this field is set to zero, and in response the server will 
allocate session id and will send it via the RedLinkReply message. In case of 
all other channel types, this field will be equal to the allocated session id"


The relevant code for generating client ids in libspice-server1 can be found 
here: 
https://gitlab.freedesktop.org/spice/spice/blob/v0.12.8/server/reds.c#L1614

This uses rand() to generate the random id, but qemu (at least in the
case of qemu-system-x86) fails to initialize the RNG seed (with e.g.
srand()).


The result is, that every SPICE session started (by e.g. libvirtd) has the same 
client_id. Usually, this is not a problem, but running something like a SPICE 
proxy, relying on the client_id to correctly route connections, this creates 
problems.


Adding something like 'srand(time(NULL));' to qemu (in vl.c) solves this issue. 
Related (as seen in some VNC patches, e.g. 
'CVE-2017-15124/04-ui-avoid-pointless-VNC-updates-if-framebuffer-isn-t-.patch/ui/vnc.c'
 ):  srand(time(NULL)+getpid()+getpid()*987654+rand());


Tested on Debian 9.7 with kernel  4.9.0-6-amd64 #1 SMP Debian 4.9.88-1+deb9u1 
(2018-05-07) x86_64 GNU/Linux.


=====

** Affects: qemu
     Importance: Undecided
         Status: New

** Affects: qemu (Debian)
     Importance: Unknown
         Status: Unknown

** Bug watch added: Debian Bug tracker #920897
   https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=920897

** Also affects: qemu (Debian) via
   https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=920897
   Importance: Unknown
       Status: Unknown

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https://bugs.launchpad.net/bugs/1815371

Title:
   SPICE session's connection_id's are not unique

Status in QEMU:
  New
Status in qemu package in Debian:
  Unknown

Bug description:
  From: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=920897

  =====

  When creating a virtual machine with qemu (e.g. via libvirt) including
  a SPICE server, the client_id of the SPICE session is not unique. For
  example, starting multiple virtual machines on the same libvirtd, the
  client_id is the same for all virtual machine's SPICE sessions.

  
  A description of the client_id can be found in

  https://www.spice-space.org/static/docs/spice_protocol.pdf under
  section 2.11. c) :

  
  "UINT32 connection_id - In case of a new session (i.e., channel type is 
RED_CHANNEL_MAIN) this field is set to zero, and in response the server will 
allocate session id and will send it via the RedLinkReply message. In case of 
all other channel types, this field will be equal to the allocated session id"

  
  The relevant code for generating client ids in libspice-server1 can be found 
here: 
https://gitlab.freedesktop.org/spice/spice/blob/v0.12.8/server/reds.c#L1614

  This uses rand() to generate the random id, but qemu (at least in the
  case of qemu-system-x86) fails to initialize the RNG seed (with e.g.
  srand()).

  
  The result is, that every SPICE session started (by e.g. libvirtd) has the 
same client_id. Usually, this is not a problem, but running something like a 
SPICE proxy, relying on the client_id to correctly route connections, this 
creates problems.

  
  Adding something like 'srand(time(NULL));' to qemu (in vl.c) solves this 
issue. Related (as seen in some VNC patches, e.g. 
'CVE-2017-15124/04-ui-avoid-pointless-VNC-updates-if-framebuffer-isn-t-.patch/ui/vnc.c'
 ):  srand(time(NULL)+getpid()+getpid()*987654+rand());

  
  Tested on Debian 9.7 with kernel  4.9.0-6-amd64 #1 SMP Debian 4.9.88-1+deb9u1 
(2018-05-07) x86_64 GNU/Linux.


  =====

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