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Re: [libvirt] Potential segfault in udev driver



On 01/25/2010 02:33 PM, Matthias Bolte wrote:
2010/1/25 Dave Allan<dallan redhat com>:
On 01/25/2010 06:37 AM, Daniel P. Berrange wrote:

On Sun, Jan 24, 2010 at 11:07:59PM +0100, Matthias Bolte wrote:

udevDeviceMonitorStartup registers udevEventHandleCallback as event
handle, but doesn't store the returned watch id to remove it later on.
Also it's not clear to me whether the event handle should be register
for the whole lifetime of the udev driver instance or just for the
udevEnumerateDevices call.

The handler should be active for the lifetime of libvirtd, since the
udev driver has to detect hotplug/unplug events over time.


If for example the call to udevSetupSystemDev [1] fails
udevDeviceMonitorShutdown is called to cleanup, but
udevEventHandleCallback is still registered and may be called when
driverState is NULL again, resulting in a segfault in
udevEventHandleCallback.

So to solve this the udevEventHandleCallback event handle must be
removed at the appropriate place.

Yes, sounds like its needs to be removed in the failure path there

Matthias,

Indeed, that's correct--can you submit a patch?

Dave


Yes, im going to do that.

One last question. The udev driver stores the udev monitor handle in
the private data pointer of the gloval driver state variable.

     driverState->privateData = udev_monitor;

To solve the event handle problem we need to store the watch id
returned by virEventAddHandle somewhere. We could either add a new
private data struct to hold the udev_monitor pointer and the watch id,
or store the watch id variable globally side by side with the driver
state variable. I prefer the first option, because it's cleaner and
the DRV_STATE_UDEV_MONITOR define allows for changing the storage
location of the udev_monitor pointer easily.

Yes, I agree--a struct is the right approach.  Thanks for doing this!

Dave


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