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Libvirt native C API and daemons
212dfa94ee
Assume there's a dnsmasq running (because there's an active
virtual network that spawned it). Now, shut down the daemon,
remove the dnsmasq binary and start the daemon again. At this
point, networkUpdateState() is called, but dnsmasq_caps is NULL
(because networkStateInitialize() called earlier failed to set
them, rightfully though).
Now, the networkUpdateState() tries to read the dnsmasq's PID
file using virPidFileReadIfAlive() which takes a path to the
corresponding binary as one of its arguments. To provide that
path, dnsmasqCapsGetBinaryPath() is called, but since
dnsmasq_caps is NULL, it dereferences it and thus causes a crash.
It's true that virPidFileReadIfAlive() can deal with a removed
binary (well virPidFileReadPathIfAlive() which it calls can), but
iff the binary path is provided in its absolute form. Otherwise,
virFileResolveAllLinks() fails to canonicalize the path
(expected, the path doesn't exist anyway).
Therefore, reading dnsmasq's PID file didn't work before
v8.1.0-rc1~401 which introduced this crash. It was always set to
-1. But passing NULL as binary path instead, makes
virPidFileReadIfAlive() return early, right after the PID file is
read and it's confirmed the PID exists.
Yes, this may yield wrong results, as the PID might be of a
completely different binary. But this problem is preexistent and
until we start locking PID files, there's nothing we can do about
it. IOW, it would require rework of dnsmasq PID file handling.
Fixes:
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| .ctags.d | ||
| .github/workflows | ||
| .gitlab/issue_templates | ||
| build-aux | ||
| ci | ||
| docs | ||
| examples | ||
| include | ||
| po | ||
| scripts | ||
| src | ||
| subprojects | ||
| tests | ||
| tools | ||
| .ctags | ||
| .dir-locals.el | ||
| .editorconfig | ||
| .gitattributes | ||
| .gitignore | ||
| .gitlab-ci.yml | ||
| .gitmodules | ||
| .gitpublish | ||
| .mailmap | ||
| AUTHORS.rst.in | ||
| config.h | ||
| configmake.h.in | ||
| CONTRIBUTING.rst | ||
| COPYING | ||
| COPYING.LESSER | ||
| gitdm.config | ||
| libvirt-admin.pc.in | ||
| libvirt-lxc.pc.in | ||
| libvirt-qemu.pc.in | ||
| libvirt.pc.in | ||
| libvirt.spec.in | ||
| meson_options.txt | ||
| meson.build | ||
| NEWS.rst | ||
| README.rst | ||
| run.in | ||
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==============================
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:
https://libvirt.org
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 2.0 (or later). See the files ``COPYING.LESSER``
and ``COPYING`` for full license terms & conditions.
Installation
============
Instructions on building and installing libvirt can be found on the website:
https://libvirt.org/compiling.html
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. Further guidance on this can be found on the website:
https://libvirt.org/contribute.html
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:
https://libvirt.org/contact.html