Hello,

> If vmdisk is NULL, shouldn't this function (qemuSnapshotDeleteValidate()) return an error?

I think this qemuSnapshotDeleteValidate should not return an error.

It seems to me that when vmdisk is NULL, this does not invalidate

the snapshot itself, but indicates that the config has changed since

the snapshot was done. And if the VM config has changed, this adds evidence that the snapshot should be deleted,

because the snapshot does not reflect the real vm config.

Since we do not have an analogue of the --force option for deleting a snapshot, in the case when qemuSnapshotDeleteValidate returns

an error when vmdisk is NULL, we will never delete a snapshot which has invalid disk.

> Similarly, disk can be NULL too

Thank you for the comment regarding the disk variable. I`ve reworked patch.

When creating a snapshot of a VM with multiple hard disks,

the snapshot takes into account the presence of all disks

in the system. If, over time, one of the disks is deleted,

the snapshot will continue to store knowledge of the deleted disk.

This results in the fact that at the moment of deleting the snapshot,

at the validation stage, a disk from the snapshot will be searched which

is not in the VM configuration. As a result, vmdisk variable will

be equal to NULL. Dereferencing a null pointer at the time of calling

virStorageSourceIsSameLocation(vmdisk->src, disk->src)

will result in SIGSEGV.

Also, the disk variable can also be equal to NULL and this

requires to check that disk != NULL before calling the

virStorageSourceIsSameLocation function to avoid SIGSEGV.

Signed-off-by: Fima Shevrin <efim.shevrin@virtuozzo.com>

---

src/qemu/qemu_snapshot.c | 2 +-

1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/qemu/qemu_snapshot.c b/src/qemu/qemu_snapshot.c

index 09ec959f10..ba13c43ff3 100644

--- a/src/qemu/qemu_snapshot.c

+++ b/src/qemu/qemu_snapshot.c

@@ -3806,7 +3806,7 @@ qemuSnapshotDeleteValidate(virDomainObj *vm,

vmdisk = qemuDomainDiskByName(vm->def, snapDisk->name);

disk = qemuDomainDiskByName(snapdef->parent.dom, snapDisk->name);

- if (!virStorageSourceIsSameLocation(vmdisk->src, disk->src)) {

+ if (vmdisk != NULL && disk != NULL && !virStorageSourceIsSameLocation(vmdisk->src, disk->src)) {

virReportError(VIR_ERR_OPERATION_UNSUPPORTED,

_("disk image '%1$s' for internal snapshot '%2$s' is not the same as disk image currently used by VM"),

snapDisk->name, snap->def->name);

--

2.39.3

From: Michal Prívozník <mprivozn@redhat.com>
Sent: Monday, May 20, 2024 15:52
To: Efim Shevrin <efim.shevrin@virtuozzo.com>; devel@lists.libvirt.org <devel@lists.libvirt.org>
Cc: den@openvz.org <den@openvz.org>
Subject: Re: [PATCH] Сheck snapshot disk is not NULL when searching it in the VM config

[You don't often get email from mprivozn@redhat.com. Learn why this is important at https://aka.ms/LearnAboutSenderIdentification ]

On 4/29/24 14:43, Fima Shevrin via Devel wrote:
> When creating a snapshot of a VM with multiple hard disks,
> the snapshot takes into account the presence of all disks
> in the system. If, over time, one of the disks is deleted,
> the snapshot will continue to store knowledge of the deleted disk.
> This results in the fact that at the moment of deleting the snapshot,
> at the validation stage, a disk from the snapshot will be searched which
> is not in the VM configuration. As a result, vmdisk variable will
> be equal to NULL. Dereferencing a null pointer at the time of calling
> virStorageSourceIsSameLocation(vmdisk->src, disk->src) will result in SIGSEGV.
>
> Signed-off-by: Fima Shevrin <efim.shevrin@virtuozzo.com>
> ---
> src/qemu/qemu_snapshot.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/src/qemu/qemu_snapshot.c b/src/qemu/qemu_snapshot.c
> index 09ec959f10..bf93cd485e 100644
> --- a/src/qemu/qemu_snapshot.c
> +++ b/src/qemu/qemu_snapshot.c
> @@ -3806,7 +3806,7 @@ qemuSnapshotDeleteValidate(virDomainObj *vm,
>              vmdisk = qemuDomainDiskByName(vm->def, snapDisk->name);
>              disk = qemuDomainDiskByName(snapdef->parent.dom, snapDisk->name);
>
> -            if (!virStorageSourceIsSameLocation(vmdisk->src, disk->src)) {
> +            if (vmdisk != NULL && !virStorageSourceIsSameLocation(vmdisk->src, disk->src)) {

If vmdisk is NULL, shouldn't this function
(qemuSnapshotDeleteValidate()) return an error?

Similarly, disk can be NULL too.

>                  virReportError(VIR_ERR_OPERATION_UNSUPPORTED,
>                                 _("disk image '%1$s' for internal snapshot '%2$s' is not the same as disk image currently used by VM"),
>                                 snapDisk->name, snap->def->name);

Michal