[PATCH v4 6/7] qemu: tpm: Avoid security labels on incoming migration with shared storage

[Michal Prívozník]

On 10/24/22 12:28, Stefan Berger wrote:
> When using shared storage there is no need to apply security labels on the
> storage since the files have to have been labeled already on the source
> side and we must assume that the source and destination side have been
> setup to use the same uid and gid for running swtpm as well as share the
> same security labels. Whether the security labels can be used at all
> depends on the shared storage and whether and how it supports them.
> 
> Signed-off-by: Stefan Berger <stefanb at linux.ibm.com>
> ---
>  src/qemu/qemu_tpm.c | 17 +++++++++++++----
>  1 file changed, 13 insertions(+), 4 deletions(-)
> 
> diff --git a/src/qemu/qemu_tpm.c b/src/qemu/qemu_tpm.c
> index cffa77cfa3..5a0d298052 100644
> --- a/src/qemu/qemu_tpm.c
> +++ b/src/qemu/qemu_tpm.c
> @@ -932,10 +932,19 @@ qemuTPMEmulatorStart(virQEMUDriver *driver,
>      virCommandSetPidFile(cmd, pidfile);
>      virCommandSetErrorFD(cmd, &errfd);
>  
> -    if (qemuSecurityStartTPMEmulator(driver, vm, cmd,
> -                                     cfg->swtpm_user, cfg->swtpm_group,
> -                                     NULL, &cmdret) < 0)
> -        return -1;
> +    if (incomingMigration &&
> +        virFileIsSharedFS(tpm->data.emulator.storagepath) == 1) {
> +        /* security labels must have been set up on source already */
> +        if (qemuSecurityCommandRun(driver, vm, cmd,
> +                                   cfg->swtpm_user, cfg->swtpm_group,
> +                                   NULL, &cmdret) < 0) {
> +            goto error;
> +        }
> +    } else if (qemuSecurityStartTPMEmulator(driver, vm, cmd,
> +                                            cfg->swtpm_user, cfg->swtpm_group,
> +                                            NULL, &cmdret) < 0) {
> +        goto error;
> +    }
>  
>      if (cmdret < 0) {
>          /* virCommandRun() hidden in qemuSecurityStartTPMEmulator()

Turns out, this is patch is problematic with SELinux [1]. Couple of
problems here:

1) When a domain is being started up, libvirt creates an unique SELinux
label. This is not migrated onto the destination - here another unique
label is created on incoming migration. This means that the state might
be not available to the destination swtpm binary.

2) the log file should be relabelled regardless - it's not on the shared
volume. And since its label is set in qemuSecurityStartTPMEmulator(), it
won't be set on the destination.


While I could deal with 2), I am not sure what to do with 1). Because
when I tried to set the label (basically by reverting this patch), the
destination was unhappy as it could not lock the .lock file.

Stefan, do you have any bright idea how to fix this?

1: https://bugzilla.redhat.com/show_bug.cgi?id=2130192

Michal