[libvirt] [PATCH v4 09/11] security: Label the external swtpm with SELinux labels

[Marc Hartmayer]

On Tue, May 15, 2018 at 05:50 PM +0200, Stefan Berger <stefanb at linux.vnet.ibm.com> wrote:
> On 05/15/2018 11:45 AM, Stefan Berger wrote:
>> On 05/15/2018 11:38 AM, Marc Hartmayer wrote:
>>> On Thu, May 10, 2018 at 11:57 PM +0200, Stefan Berger
>>> <stefanb at linux.vnet.ibm.com> wrote:
>>>> In this patch we label the swtpm process with SELinux labels. We
>>>> give it the
>>>> same label as the QEMU process has. We label its state directory and
>>>> files
>>>> as well. We restore the old security labels once the swtpm has
>>>> terminated.
>>>>
>>>> The file and process labels now look as follows:
>>>>
>>>> Directory: /var/lib/libvirt/swtpm
>>>>
>>>> [root at localhost swtpm]# ls -lZ
>>>> total 4
>>>> rwx------. 2 tss  tss system_u:object_r:svirt_image_t:s0:c254,c932
>>>> 4096 Apr  5 16:46 testvm
>>>>
>>>> [root at localhost testvm]# ls -lZ
>>>> total 8
>>>> -rw-r--r--. 1 tss tss system_u:object_r:svirt_image_t:s0:c254,c932
>>>> 3648 Apr  5 16:46 tpm-00.permall
>>>>
>>>> The log in /var/log/swtpm/libvirt/qemu is labeled as follows:
>>>>
>>>> -rw-r--r--. 1 tss tss system_u:object_r:svirt_image_t:s0:c254,c932
>>>> 2237 Apr  5 16:46 vtpm.log
>>>>
>>>> [root at localhost 485d0004-a48f-436a-8457-8a3b73e28567]# ps auxZ |
>>>> grep swtpm | grep ctrl | grep -v grep
>>>> system_u:system_r:svirt_t:s0:c254,c932 tss 25664 0.0  0.0 28172
>>>> 3892 ?        Ss   16:57   0:00 /usr/bin/swtpm socket --daemon
>>>> --ctrl
>>>> type=unixio,path=/var/run/libvirt/qemu/swtpm/testvm-swtpm.sock,mode=0660
>>>> --tpmstate dir=/var/lib/libvirt/swtpm/testvm/tpm1.2 --log
>>>> file=/var/log/swtpm/libvirt/qemu/testvm-swtpm.log
>>>>
>>>> [root at localhost 485d0004-a48f-436a-8457-8a3b73e28567]# ps auxZ |
>>>> grep qemu | grep tpm | grep -v grep
>>>> system_u:system_r:svirt_t:s0:c254,c932 qemu 25669 99.0  0.0 3096704
>>>> 48500 ?    Sl   16:57   3:28 /bin/qemu-system-x86_64 [..]
>>>>
>>>> Signed-off-by: Stefan Berger <stefanb at linux.vnet.ibm.com>
>>>> ---
>>>>   src/libvirt_private.syms        |   2 +
>>>>   src/qemu/qemu_tpm.c             |  24 +++++-
>>>>   src/security/security_driver.h  |   7 ++
>>>>   src/security/security_manager.c |  36 +++++++++
>>>>   src/security/security_manager.h |   6 ++
>>>>   src/security/security_selinux.c | 164
>>>> ++++++++++++++++++++++++++++++++++++++++
>>>>   src/security/security_stack.c   |  40 ++++++++++
>>>>   7 files changed, 278 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
>>>> index 75b8932..2ce67e7 100644
>>>> --- a/src/libvirt_private.syms
>>>> +++ b/src/libvirt_private.syms
>>>> @@ -1319,6 +1319,7 @@ virSecurityManagerRestoreImageLabel;
>>>>   virSecurityManagerRestoreInputLabel;
>>>>   virSecurityManagerRestoreMemoryLabel;
>>>>   virSecurityManagerRestoreSavedStateLabel;
>>>> +virSecurityManagerRestoreTPMLabels;
>>>>   virSecurityManagerSetAllLabel;
>>>>   virSecurityManagerSetChardevLabel;
>>>>   virSecurityManagerSetChildProcessLabel;
>>>> @@ -1333,6 +1334,7 @@ virSecurityManagerSetProcessLabel;
>>>>   virSecurityManagerSetSavedStateLabel;
>>>>   virSecurityManagerSetSocketLabel;
>>>>   virSecurityManagerSetTapFDLabel;
>>>> +virSecurityManagerSetTPMLabels;
>>>>   virSecurityManagerStackAddNested;
>>>>   virSecurityManagerTransactionAbort;
>>>>   virSecurityManagerTransactionCommit;
>>>> diff --git a/src/qemu/qemu_tpm.c b/src/qemu/qemu_tpm.c
>>>> index 024d24d..62f0146 100644
>>>> --- a/src/qemu/qemu_tpm.c
>>>> +++ b/src/qemu/qemu_tpm.c
>>>> @@ -684,7 +684,26 @@ qemuExtTPMStartEmulator(virQEMUDriverPtr driver,
>>>>
>>>>       virCommandSetErrorBuffer(cmd, &errbuf);
>>>>
>>>> -    if (virCommandRun(cmd, &exitstatus) < 0 || exitstatus != 0) {
>>>> +    if (virSecurityManagerSetTPMLabels(driver->securityManager,
>>>> +                                       def) < 0)
>>>> +        goto cleanup;
>>>> +
>>>> +    if
>>>> (virSecurityManagerSetChildProcessLabel(driver->securityManager,
>>>> +                                               def, cmd) < 0)
>>>> +        goto cleanup;
>>>> +
>>>> +    if (virSecurityManagerPreFork(driver->securityManager) < 0)
>>>> +        goto cleanup;
>>>> +
>>>> +    /* make sure we run this with the appropriate user */
>>>> +    virCommandSetUID(cmd, cfg->swtpm_user);
>>>> +    virCommandSetGID(cmd, cfg->swtpm_group);
>>>> +
>>>> +    ret = virCommandRun(cmd, &exitstatus);
>>>> +
>>>> +    virSecurityManagerPostFork(driver->securityManager);
>>>> +
>>>> +    if (ret < 0 || exitstatus != 0) {
>>>>           VIR_ERROR(_("Could not start 'swtpm'. exitstatus: %d "
>>>>                       "stderr: %s"), exitstatus, errbuf);
>>>>           virReportError(VIR_ERR_INTERNAL_ERROR,
>>> Don't we have to set ret to -1 here (for the case where ret == 0 &&
>>> exitstatus != 0)?
>>
>> Very true.
>
> ret is initialized with '-1'. So we are good.

No we are not good since @ret is overwritten with:

ret = virCommandRun(cmd, &exitstatus);

So it’s possible that virCommandRun returns 0 but exitstatus != 0
=> ret == 0; exitstatus != 0
=> virReportError(…) reports an error but the return value @ret remains 0.

>
>     Stefan

Beste Grüße / Kind regards
   Marc Hartmayer

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