2065499b60
If a remote call fails during event registration (more than likely from
a network failure or remote libvirtd restart timed just right), then when
calling the virObjectEventStateDeregisterID we don't want to call the
registered @freecb function because that breaks our contract that we
would only call it after succesfully returning. If the @freecb routine
were called, it could result in a double free from properly coded
applications that free their opaque data on failure to register, as seen
in the following details:
Program terminated with signal 6, Aborted.
#0 0x00007fc45cba15d7 in raise
#1 0x00007fc45cba2cc8 in abort
#2 0x00007fc45cbe12f7 in __libc_message
#3 0x00007fc45cbe86d3 in _int_free
#4 0x00007fc45d8d292c in PyDict_Fini
#5 0x00007fc45d94f46a in Py_Finalize
#6 0x00007fc45d960735 in Py_Main
#7 0x00007fc45cb8daf5 in __libc_start_main
#8 0x0000000000400721 in _start
The double dereference of 'pyobj_cbData' is triggered in the following way:
(1) libvirt_virConnectDomainEventRegisterAny is invoked.
(2) the event is successfully added to the event callback list
(virDomainEventStateRegisterClient in
remoteConnectDomainEventRegisterAny returns 1 which means ok).
(3) when function remoteConnectDomainEventRegisterAny is hit,
network connection disconnected coincidently (or libvirtd is
restarted) in the context of function 'call' then the connection
is lost and the function 'call' failed, the branch
virObjectEventStateDeregisterID is therefore taken.
(4) 'pyobj_conn' is dereferenced the 1st time in
libvirt_virConnectDomainEventFreeFunc.
(5) 'pyobj_cbData' (refered to pyobj_conn) is dereferenced the
2nd time in libvirt_virConnectDomainEventRegisterAny.
(6) the double free error is triggered.
Resolve this by adding a @doFreeCb boolean in order to avoid calling the
freeCb in virObjectEventStateDeregisterID for any remote call failure in
a remoteConnect*EventRegister* API. For remoteConnect*EventDeregister* calls,
the passed value would be true indicating they should run the freecb if it
exists; whereas, it's false for the remote call failure path.
Patch based on the investigation and initial patch posted by
fangying <fangying1@huawei.com>.
Libvirt API for virtualization
Libvirt provides a portable, long term stable C API for managing the virtualization technologies provided by many operating systems. It includes support for QEMU, KVM, Xen, LXC, bhyve, Virtuozzo, VMware vCenter and ESX, VMware Desktop, Hyper-V, VirtualBox and the POWER Hypervisor.
For some of these hypervisors, it provides a stateful management daemon which runs on the virtualization host allowing access to the API both by non-privileged local users and remote users.
Layered packages provide bindings of the libvirt C API into other languages including Python, Perl, PHP, Go, Java, OCaml, as well as mappings into object systems such as GObject, CIM and SNMP.
Further information about the libvirt project can be found on the website:
License
The libvirt C API is distributed under the terms of GNU Lesser General Public License, version 2.1 (or later). Some parts of the code that are not part of the C library may have the more restrictive GNU General Public License, version 2.1 (or later). See the files COPYING.LESSER and COPYING for full license terms & conditions.
Installation
Libvirt uses the GNU Autotools build system, so in general can be built and installed with the usual commands. For example, to build in a manner that is suitable for installing as root, use:
$ ./configure --prefix=/usr --sysconfdir=/etc --localstatedir=/var
$ make
$ sudo make install
While to build & install as an unprivileged user
$ ./configure --prefix=$HOME/usr
$ make
$ make install
The libvirt code relies on a large number of 3rd party libraries. These will be detected during execution of the configure script and a summary printed which lists any missing (optional) dependencies.
Contributing
The libvirt project welcomes contributions in many ways. For most components
the best way to contribute is to send patches to the primary development
mailing list, using the git send-email command. Further guidance on this
can be found in the HACKING file, or the project website
Contact
The libvirt project has two primary mailing lists:
- libvirt-users@redhat.com (for user discussions)
- libvir-list@redhat.com (for development only)
Further details on contacting the project are available on the website