[libvirt] [RFC PATCH 2/6] LXC: introduce virLXCControllerSetupUserns and lxcContainerSetUserns

[Gao feng]

On 2013/03/13 18:57, Daniel P. Berrange wrote:
> On Mon, Mar 11, 2013 at 02:26:48PM +0800, Gao feng wrote:
>> This patch introduces new helper function
>> virLXCControllerSetupUserns, in this function,
>> we set the files uid_map and gid_map of process
>> libvirt_lxc.
>>
>> lxcContainerSetUserns is used for creating cred for
>> tasks running in container. Since after setuid/setgid,
>> we may be a new user. This patch calls lxcContainerSetUserns
>> at first to make sure the new created files belong to
>> right user.
>>
>> Signed-off-by: Gao feng <gaofeng at cn.fujitsu.com>
>> ---
>>  src/lxc/lxc_container.c  | 55 ++++++++++++++++++++++++++++++----------
>>  src/lxc/lxc_controller.c | 66 ++++++++++++++++++++++++++++++++++++++++++++++++
>>  2 files changed, 107 insertions(+), 14 deletions(-)
>>
>> diff --git a/src/lxc/lxc_container.c b/src/lxc/lxc_container.c
>> index 1d7bc1e..5c66ae3 100644
>> --- a/src/lxc/lxc_container.c
>> +++ b/src/lxc/lxc_container.c
>> @@ -329,6 +329,29 @@ int lxcContainerWaitForContinue(int control)
>>  
>>  
>>  /**
>> + * lxcContainerSetUserns:
>> + *
>> + * This function calls setuid and setgid to create proper
>> + * cred for tasks running in container.
>> + *
>> + * Returns 0 on success or -1 in case of error
>> + */
>> +static int lxcContainerSetUserns(virDomainDefPtr def)
>> +{
>> +    if (def->os.userns != VIR_DOMAIN_USER_NS_ENABLED)
>> +        return 0;
>> +
>> +    if (virSetUIDGID(def->os.uidmap.first,
>> +                     def->os.gidmap.first) < 0) {
>> +        virReportSystemError(errno, "%s",
>> +                             _("setuid or setgid failed"));
>> +        return -1;
>> +    }
>> +
>> +    return 0;
>> +}
> 
> I don't see why we should force the init process to have the first
> UID in the map. The init process should always start as uid:gid 0:0
> regardless of mapping IMHO. If we want a capability to start the
> init process as a different uid:gid, then that should involve separate
> XML configuration.
> 

Yes,kernel provides flexible interface.but we can force the [u,g]ser id of
init process to 0:0.

>> @@ -2221,6 +2244,24 @@ static int lxcContainerChild(void *data)
>>          }
>>      }
>>  
>> +    if (!virFileExists(vmDef->os.init)) {
>> +        virReportSystemError(errno,
>> +                    _("cannot find init path '%s' relative to container root"),
>> +                    vmDef->os.init);
>> +        goto cleanup;
>> +    }
>> +
>> +    /* Wait for interface devices to show up */
>> +    if (lxcContainerWaitForContinue(argv->monitor) < 0) {
>> +        virReportSystemError(errno, "%s",
>> +                             _("Failed to read the container continue message"));
>> +        goto cleanup;
>> +    }
>> +    VIR_DEBUG("Received container continue message");
> 
> I don't really see why you're moving these lines - they are unrelated
> to user namespaces.
> 

This change ensure the init process has new cred first.
see lxcContainerSetUserns below.
>> +
>> +    if (lxcContainerSetUserns(vmDef) < 0)
>> +        goto cleanup;
>> +
>>      VIR_DEBUG("Container TTY path: %s", ttyPath);
>>  
>>      ttyfd = open(ttyPath, O_RDWR|O_NOCTTY);
>> @@ -2236,20 +2277,6 @@ static int lxcContainerChild(void *data)
>>                                  argv->securityDriver) < 0)
>>          goto cleanup;
>>  
>> -    if (!virFileExists(vmDef->os.init)) {
>> -        virReportSystemError(errno,
>> -                    _("cannot find init path '%s' relative to container root"),
>> -                    vmDef->os.init);
>> -        goto cleanup;
>> -    }
>> -
>> -    /* Wait for interface devices to show up */
>> -    if (lxcContainerWaitForContinue(argv->monitor) < 0) {
>> -        virReportSystemError(errno, "%s",
>> -                             _("Failed to read the container continue message"));
>> -        goto cleanup;
>> -    }
>> -    VIR_DEBUG("Received container continue message");
>>  
>>      /* rename and enable interfaces */
>>      if (lxcContainerRenameAndEnableInterfaces(!!(vmDef->features &
>> diff --git a/src/lxc/lxc_controller.c b/src/lxc/lxc_controller.c
>> index 15aa334..f17142f 100644
>> --- a/src/lxc/lxc_controller.c
>> +++ b/src/lxc/lxc_controller.c
>> @@ -1028,6 +1028,69 @@ cleanup2:
>>  }
>>  
>>  
>> +/**
>> + * virLXCControllerSetupUserns
>> + *
>> + * Set proc files for user namespace
>> + *
>> + * Returns 0 on success or -1 in case of error
>> + */
>> +static int virLXCControllerSetupUserns(virLXCControllerPtr ctrl)
>> +{
>> +    char *uid_map = NULL;
>> +    char *gid_map = NULL;
>> +    char *uidmap_value = NULL;
>> +    char *gidmap_value = NULL;
>> +    int ret = -1;
>> +
>> +    if (ctrl->def->os.userns != VIR_DOMAIN_USER_NS_ENABLED)
>> +        return 0;
>> +
>> +    if (virAsprintf(&uid_map, "/proc/%d/uid_map", ctrl->initpid) < 0)
>> +        goto cleanup;
>> +
>> +    if (virAsprintf(&gid_map, "/proc/%d/gid_map", ctrl->initpid) < 0)
>> +        goto cleanup;
>> +
>> +    if (virAsprintf(&uidmap_value, "%u %u %u",
>> +                    ctrl->def->os.uidmap.first,
>> +                    ctrl->def->os.uidmap.low_first,
>> +                    ctrl->def->os.uidmap.count) < 0)
>> +        goto cleanup;
>> +
>> +    if (virAsprintf(&gidmap_value, "%u %u %u",
>> +                    ctrl->def->os.gidmap.first,
>> +                    ctrl->def->os.gidmap.low_first,
>> +                    ctrl->def->os.gidmap.count) < 0)
>> +        goto cleanup;
>> +
>> +    if (virFileWriteStr(uid_map, uidmap_value, 0) < 0) {
>> +        if (errno == -ENOENT)
>> +            virReportSystemError(errno,
>> +                                 _("%s doesn't exist, please disable userns"),
>> +                                 uid_map);
>> +        virReportSystemError(errno, _("unable write to %s"), uid_map);
>> +        goto cleanup;
>> +    }
>> +
>> +    if (virFileWriteStr(gid_map, gidmap_value, 0) < 0) {
>> +        if (errno == -ENOENT)
>> +            virReportSystemError(errno,
>> +                                 _("%s doesn't exist, please disable userns"),
>> +                                 gid_map);
>> +        virReportSystemError(errno, _("unable write to %s"), gid_map);
>> +        goto cleanup;
>> +    }
>> +
>> +    ret = 0;
>> +cleanup:
>> +    VIR_FREE(uidmap_value);
>> +    VIR_FREE(gidmap_value);
>> +    VIR_FREE(uid_map);
>> +    VIR_FREE(gid_map);
>> +    return ret;
>> +}
> 
> I think we should have one method can write to either mapping file,
> and that should be invoked once to setup UID mapping and once to
> setup GID mapping. This would remove all the duplication in this
> method. Also we need to be able to write multiple lines to the
> mapping files in one go.
> 

sounds reasonable,will do.

Thanks!