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Re: [Qemu-devel] [PATCH v2] qdev: Fix use after free in qdev_init_nofail
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH v2] qdev: Fix use after free in qdev_init_nofail error path |
Date: |
Tue, 2 Aug 2016 18:55:13 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1 |
On 02/08/2016 12:49, Igor Mammedov wrote:
> Since 69382d8b (qdev: Fix object reference leak in case device.realize()
> fails), object_property_set_bool releases the device object
> in case realize's failed and device hasn't explicitly assigned
> parent. It happens due to object_unparent() on error handling
> path releases not only implicitly set parent but also calls
> device_unparent() which releases the remaining reference hold
> buy parent bus.
>
> qdev_try_create() created device has only 1 reference hold by
> parent bus which makes impossible to unparent/re-parent object
> without destroying it.
>
> Fix it by making caller of qdev_try_create()/qdev_init_nofail()
> own a reference from object_new() until qdev_init_nofail() is
> successfully executed so that uparenting won't destroy device
> until caller owns pointer returned by qdev_try_create().
Your patch is indeed nicer in theory, but in practice I'm not sure that
there are no occurrences of object_new + qdev_init_nofail, or
qdev_try_create + object_property_set_bool. These would be broken, so
I'm going with Fam's.
Paolo
> Signed-off-by: Igor Mammedov <address@hidden>
> ---
> hw/core/qdev.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/hw/core/qdev.c b/hw/core/qdev.c
> index ee4a083..0139d67 100644
> --- a/hw/core/qdev.c
> +++ b/hw/core/qdev.c
> @@ -151,7 +151,6 @@ DeviceState *qdev_try_create(BusState *bus, const char
> *type)
> }
>
> qdev_set_parent_bus(dev, bus);
> - object_unref(OBJECT(dev));
> return dev;
> }
>
> @@ -360,6 +359,7 @@ void qdev_init_nofail(DeviceState *dev)
> object_get_typename(OBJECT(dev)));
> exit(1);
> }
> + object_unref(OBJECT(dev));
> }
>
> void qdev_machine_creation_done(void)
>