[Qemu-devel] [PATCH] block/qdev: Fix NULL access when using BB twice

[Qemu-devel] [PATCH] block/qdev: Fix NULL access when using BB twice

[Kevin Wolf]

BlockBackend has only a single pointer to its guest device, so it makes
sure that only a single guest device is attached to it. device-add
returns an error if you try to attach a second device to a BB. In order
to make the error message nicer, -device that manually connects to a
if=none block device get a different message than -drive that implicitly
creates a guest device. The if=... option is stored in DriveInfo.

However, since blockdev-add exists, not every BlockBackend has a
DriveInfo any more. Check that it exists before we dereference it.

QMP reproducer resulting in a segfault:

{"execute":"blockdev-add","arguments":{"options":{"id":"disk","driver":"file","filename":"/tmp/test.img"}}}
{"execute":"device_add","arguments":{"driver":"virtio-blk-pci","drive":"disk"}}
{"execute":"device_add","arguments":{"driver":"virtio-blk-pci","drive":"disk"}}

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 hw/core/qdev-properties-system.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/core/qdev-properties-system.c b/hw/core/qdev-properties-system.c
index 623be94..c5cc9cf 100644
--- a/hw/core/qdev-properties-system.c
+++ b/hw/core/qdev-properties-system.c
@@ -91,7 +91,7 @@ static void parse_drive(DeviceState *dev, const char *str, void **ptr,
     if (blk_attach_dev(blk, dev) < 0) {
         DriveInfo *dinfo = blk_legacy_dinfo(blk);
 
-        if (dinfo->type != IF_NONE) {
+        if (dinfo && dinfo->type != IF_NONE) {
             error_setg(errp, "Drive '%s' is already in use because "
                        "it has been automatically connected to another "
                        "device (did you need 'if=none' in the drive options?)",
-- 
1.8.3.1

Re: [Qemu-devel] [PATCH] block/qdev: Fix NULL access when using BB twice

[Eric Blake]

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On 06/23/2016 01:30 AM, Kevin Wolf wrote:
> BlockBackend has only a single pointer to its guest device, so it makes
> sure that only a single guest device is attached to it. device-add
> returns an error if you try to attach a second device to a BB. In order
> to make the error message nicer, -device that manually connects to a
> if=none block device get a different message than -drive that implicitly
> creates a guest device. The if=... option is stored in DriveInfo.
> 
> However, since blockdev-add exists, not every BlockBackend has a
> DriveInfo any more. Check that it exists before we dereference it.
> 
> QMP reproducer resulting in a segfault:
> 
> {"execute":"blockdev-add","arguments":{"options":{"id":"disk","driver":"file","filename":"/tmp/test.img"}}}
> {"execute":"device_add","arguments":{"driver":"virtio-blk-pci","drive":"disk"}}
> {"execute":"device_add","arguments":{"driver":"virtio-blk-pci","drive":"disk"}}
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  hw/core/qdev-properties-system.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Reviewed-by: Eric Blake <eblake@redhat.com>

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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Re: [Qemu-devel] [Qemu-block] [PATCH] block/qdev: Fix NULL access when using BB twice

[Stefan Hajnoczi]

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On Thu, Jun 23, 2016 at 09:30:01AM +0200, Kevin Wolf wrote:
> BlockBackend has only a single pointer to its guest device, so it makes
> sure that only a single guest device is attached to it. device-add
> returns an error if you try to attach a second device to a BB. In order
> to make the error message nicer, -device that manually connects to a
> if=none block device get a different message than -drive that implicitly
> creates a guest device. The if=... option is stored in DriveInfo.
> 
> However, since blockdev-add exists, not every BlockBackend has a
> DriveInfo any more. Check that it exists before we dereference it.
> 
> QMP reproducer resulting in a segfault:
> 
> {"execute":"blockdev-add","arguments":{"options":{"id":"disk","driver":"file","filename":"/tmp/test.img"}}}
> {"execute":"device_add","arguments":{"driver":"virtio-blk-pci","drive":"disk"}}
> {"execute":"device_add","arguments":{"driver":"virtio-blk-pci","drive":"disk"}}
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  hw/core/qdev-properties-system.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)

Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>

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Re: [Qemu-devel] [PATCH] block/qdev: Fix NULL access when using BB twice

[Kevin Wolf]

Am 23.06.2016 um 09:30 hat Kevin Wolf geschrieben:
> BlockBackend has only a single pointer to its guest device, so it makes
> sure that only a single guest device is attached to it. device-add
> returns an error if you try to attach a second device to a BB. In order
> to make the error message nicer, -device that manually connects to a
> if=none block device get a different message than -drive that implicitly
> creates a guest device. The if=... option is stored in DriveInfo.
> 
> However, since blockdev-add exists, not every BlockBackend has a
> DriveInfo any more. Check that it exists before we dereference it.
> 
> QMP reproducer resulting in a segfault:
> 
> {"execute":"blockdev-add","arguments":{"options":{"id":"disk","driver":"file","filename":"/tmp/test.img"}}}
> {"execute":"device_add","arguments":{"driver":"virtio-blk-pci","drive":"disk"}}
> {"execute":"device_add","arguments":{"driver":"virtio-blk-pci","drive":"disk"}}
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>

Applied to my block branch.

Kevin