6:26 a.m.
On 06/23/2017 05:39 AM, Michal Privoznik wrote:
On 06/23/2017 12:10 AM, John Ferlan wrote:
> 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 an @inhibitFreeCb boolean in order to avoid calling
> freecb in virObjectEventStateDeregisterID for any remote call failure in
> a remoteConnect*EventRegister* API. For remoteConnect*EventDeregister* calls,
> the passed value would be false indicating they should run the freecb if it
> exists.
>
> Patch based on the investigation and initial patch posted by:
> fangying <fangying1(a)huawei.com>.
>
> Signed-off-by: John Ferlan <jferlan(a)redhat.com>
> ---
> Initial patch found at:
>
> https://www.redhat.com/archives/libvir-list/2017-June/msg00039.html
>
> based on feedback from Daniel Berrange to a previous posting:
>
> https://www.redhat.com/archives/libvir-list/2017-May/msg01089.html
>
> Since no new patch was posted, I posted my idea from review for
> consideration.
>
> src/bhyve/bhyve_driver.c | 2 +-
> src/conf/domain_event.c | 2 +-
> src/conf/object_event.c | 23 +++++++++++++++++------
> src/conf/object_event.h | 3 ++-
> src/libxl/libxl_driver.c | 2 +-
> src/lxc/lxc_driver.c | 2 +-
> src/network/bridge_driver.c | 2 +-
> src/node_device/node_device_driver.c | 2 +-
> src/qemu/qemu_driver.c | 4 ++--
> src/remote/remote_driver.c | 32 ++++++++++++++++----------------
> src/secret/secret_driver.c | 2 +-
> src/storage/storage_driver.c | 2 +-
> src/test/test_driver.c | 8 ++++----
> src/uml/uml_driver.c | 2 +-
> src/vz/vz_driver.c | 2 +-
> src/xen/xen_driver.c | 2 +-
> 16 files changed, 52 insertions(+), 40 deletions(-)
>
> diff --git a/src/bhyve/bhyve_driver.c b/src/bhyve/bhyve_driver.c
> index ed2221a..6722dc4 100644
> --- a/src/bhyve/bhyve_driver.c
> +++ b/src/bhyve/bhyve_driver.c
> @@ -1503,7 +1503,7 @@ bhyveConnectDomainEventDeregisterAny(virConnectPtr conn,
>
> if (virObjectEventStateDeregisterID(conn,
> privconn->domainEventState,
> - callbackID) < 0)
> + callbackID, false) < 0)
> return -1;
>
> return 0;
> diff --git a/src/conf/domain_event.c b/src/conf/domain_event.c
> index 6e471d7..ff4c602 100644
> --- a/src/conf/domain_event.c
> +++ b/src/conf/domain_event.c
> @@ -2301,7 +2301,7 @@ virDomainEventStateDeregister(virConnectPtr conn,
> NULL);
> if (callbackID < 0)
> return -1;
> - return virObjectEventStateDeregisterID(conn, state, callbackID);
> + return virObjectEventStateDeregisterID(conn, state, callbackID, false);
Why is this false? virDomainEventStateDeregister is called directly from
public API implementations. For instance from
qemuConnectDomainEventDeregister(). Don't we want to run free callback then?
and the eventual check in virObjectEventCallbackListRemoveID is:
/* inhibiting calling @freecb from error paths in register
* functions ensures the caller of the register function won't
* end up with a double free error */
if (!inhibitFreeCb && cb->freecb)
IOW: Any time called from a Deregister path, we call the free callback;
however, when called from a RPC call REGISTER path, then we don't want
to call the free callback because we're returning -1 to the caller and
the caller will free things.
Or am I misreading your question. For a Deregister path if the
cb->freecb exists, then we want to call it like we have.
John
> }
>
Michal