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The two scenarios were found by Coverity after a seemingly-unrelated
change to virLXCProcessSetupInterfaceTap() (in commit ecfc2d5f43), and
explained by John Ferlan here:
https://www.redhat.com/archives/libvir-list/2020-December/msg00810.html
To re-explain:
a) On entry to virLXCProcessSetupInterfaceTap() if net->ifname != NULL
then a copy of net->ifname is made into parentVeth, and a reference
to *that* pointer is sent down to virNetDevVethCreate().
b) If parentVeth (aka net->ifname) is a template name (e.g. "blah%d"),
then virNetDevVethCreate() calls virNetDevGenerateName(), and if
virNetDevGenerateName() successfully generates a usable name
(e.g. "blah27") then it will free the original template string
(which is pointed to by net->ifname and by parentVeth), then
replace the pointer in parentVeth with a pointer to the new
string. Note that net->ifname still points to the now-freed
template string.
c) returning back up to virLXCProcessSetupInterfaceTap(), we check if
net->ifname == NULL - it *isn't* (still contains stale pointer to
template string), so we don't replace it with the pointer to the new
string that is in parentVeth.
d) Result: the new string is leaked once we return from
virLXCProcessSetupInterfaceTap(), while there is a dangling pointer
to the old string in net->ifname.
There is also a leak if there is a failure somewhere between steps (b)
and (c) above - the failure cleanup in virNetDevVethCreate() will only
free the newly-generated parentVeth string if the original pointer was
NULL (narrator: "It wasn't."). But it's a new string allocated by
virNetDevGenerateName(), not the original string from net->ifname, so
it really does need to be freed.
The solution is to make a copy of the entire original string into a
g_autofree pointer, then iff everything is successful we g_free() the
original net->ifname and replace it by stealing the string returned by
virNetDevVethCreate().
Signed-off-by: Laine Stump <laine@redhat.com>
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
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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