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Re: [libvirt] [RFC PATCH 4/6] LXC: Creating devices for container on host side



On 2013/03/13 19:02, Daniel P. Berrange wrote:
> On Mon, Mar 11, 2013 at 02:26:50PM +0800, Gao feng wrote:
>> user namespace doesn't allow to create devices in
>> uninit userns. We should create devices on host side.
>>
>> Signed-off-by: Gao feng <gaofeng cn fujitsu com>
>> ---
>>  src/lxc/lxc_container.c  | 47 +++++++--------------------
>>  src/lxc/lxc_controller.c | 83 ++++++++++++++++++++++++++++++++++++++++++++++++
>>  2 files changed, 94 insertions(+), 36 deletions(-)
> 
> We actually need this change independently of user namespaces. Currently
> the cgroup devices setup we do allows 'mknod' permission, when it really
> ought to be blocked. If we move the setup code into the controller then
> we can fix the cgroup devices setup to block mknod too.
> 

Yes, Agree with you.

I will add this one into my patchset.

>> diff --git a/src/lxc/lxc_container.c b/src/lxc/lxc_container.c
>> index 92af3e5..58d6ee5 100644
>> --- a/src/lxc/lxc_container.c
>> +++ b/src/lxc/lxc_container.c
>> @@ -681,22 +681,10 @@ static int lxcContainerMountFSDevPTS(virDomainFSDefPtr root)
>>      return rc;
>>  }
>>  
>> -static int lxcContainerPopulateDevices(char **ttyPaths, size_t nttyPaths)
>> +static int lxcContainerSetupDevices(char **ttyPaths, size_t nttyPaths)
>>  {
>>      size_t i;
>>      const struct {
>> -        int maj;
>> -        int min;
>> -        mode_t mode;
>> -        const char *path;
>> -    } devs[] = {
>> -        { LXC_DEV_MAJ_MEMORY, LXC_DEV_MIN_NULL, 0666, "/dev/null" },
>> -        { LXC_DEV_MAJ_MEMORY, LXC_DEV_MIN_ZERO, 0666, "/dev/zero" },
>> -        { LXC_DEV_MAJ_MEMORY, LXC_DEV_MIN_FULL, 0666, "/dev/full" },
>> -        { LXC_DEV_MAJ_MEMORY, LXC_DEV_MIN_RANDOM, 0666, "/dev/random" },
>> -        { LXC_DEV_MAJ_MEMORY, LXC_DEV_MIN_URANDOM, 0666, "/dev/urandom" },
>> -    };
>> -    const struct {
>>          const char *src;
>>          const char *dst;
>>      } links[] = {
>> @@ -706,18 +694,6 @@ static int lxcContainerPopulateDevices(char **ttyPaths, size_t nttyPaths)
>>          { "/proc/self/fd", "/dev/fd" },
>>      };
>>  
>> -    /* Populate /dev/ with a few important bits */
>> -    for (i = 0 ; i < ARRAY_CARDINALITY(devs) ; i++) {
>> -        dev_t dev = makedev(devs[i].maj, devs[i].min);
>> -        if (mknod(devs[i].path, S_IFCHR, dev) < 0 ||
>> -            chmod(devs[i].path, devs[i].mode)) {
>> -            virReportSystemError(errno,
>> -                                 _("Failed to make device %s"),
>> -                                 devs[i].path);
>> -            return -1;
>> -        }
>> -    }
>> -
>>      for (i = 0 ; i < ARRAY_CARDINALITY(links) ; i++) {
>>          if (symlink(links[i].src, links[i].dst) < 0) {
>>              virReportSystemError(errno,
>> @@ -737,15 +713,6 @@ static int lxcContainerPopulateDevices(char **ttyPaths, size_t nttyPaths)
>>                                   _("Failed to bind /dev/pts/ptmx on to /dev/ptmx"));
>>              return -1;
>>          }
>> -    } else {
>> -        /* Legacy devpts, so we need to just use shared one */
>> -        dev_t dev = makedev(LXC_DEV_MAJ_TTY, LXC_DEV_MIN_PTMX);
>> -        if (mknod("/dev/ptmx", S_IFCHR, dev) < 0 ||
>> -            chmod("/dev/ptmx", 0666)) {
>> -            virReportSystemError(errno, "%s",
>> -                                 _("Failed to make device /dev/ptmx"));
>> -            return -1;
>> -        }
>>      }
>>  
>>      for (i = 0 ; i < nttyPaths ; i++) {
>> @@ -1988,8 +1955,8 @@ static int lxcContainerSetupPivotRoot(virDomainDefPtr vmDef,
>>      if (lxcContainerMountFSDevPTS(root) < 0)
>>          goto cleanup;
>>  
>> -    /* Populates device nodes in /dev/ */
>> -    if (lxcContainerPopulateDevices(ttyPaths, nttyPaths) < 0)
>> +    /* Setup device nodes in /dev/ */
>> +    if (lxcContainerSetupDevices(ttyPaths, nttyPaths) < 0)
>>          goto cleanup;
>>  
>>      /* Sets up any non-root mounts from guest config */
>> @@ -2306,6 +2273,14 @@ static int lxcContainerChild(void *data)
>>          goto cleanup;
>>      }
>>  
>> +    /* Wait for controller creating devices for container */
>> +    if (lxcContainerWaitForContinue(argv->monitor) < 0) {
>> +        virReportSystemError(errno, "%s",
>> +                             _("Failed to read the container continue message"));
>> +        goto cleanup;
>> +    }
>> +    VIR_DEBUG("Received container continue message, create devices success.");
>> +
>>      ret = 0;
>>  cleanup:
>>      VIR_FREE(ttyPath);
>> diff --git a/src/lxc/lxc_controller.c b/src/lxc/lxc_controller.c
>> index f17142f..c6f8c3b 100644
>> --- a/src/lxc/lxc_controller.c
>> +++ b/src/lxc/lxc_controller.c
>> @@ -1092,6 +1092,79 @@ cleanup:
>>  }
>>  
>>  
>> +static int virLXCControllerPopulateDevices(virLXCControllerPtr ctrl)
>> +{
>> +    size_t i;
>> +    char *ptmx = NULL;
>> +    const struct {
>> +        int maj;
>> +        int min;
>> +        mode_t mode;
>> +        const char *path;
>> +    } devs[] = {
>> +        { LXC_DEV_MAJ_MEMORY, LXC_DEV_MIN_NULL, 0666, "/dev/null" },
>> +        { LXC_DEV_MAJ_MEMORY, LXC_DEV_MIN_ZERO, 0666, "/dev/zero" },
>> +        { LXC_DEV_MAJ_MEMORY, LXC_DEV_MIN_FULL, 0666, "/dev/full" },
>> +        { LXC_DEV_MAJ_MEMORY, LXC_DEV_MIN_RANDOM, 0666, "/dev/random" },
>> +        { LXC_DEV_MAJ_MEMORY, LXC_DEV_MIN_URANDOM, 0666, "/dev/urandom" },
>> +    };
>> +    virDomainFSDefPtr root = virDomainGetRootFilesystem(ctrl->def);
>> +
>> +    if (root == NULL || root->src == NULL)
>> +        return 0;
>> +
>> +    /* Populate /dev/ with a few important bits */
>> +    for (i = 0 ; i < ARRAY_CARDINALITY(devs) ; i++) {
>> +        char *path = NULL;
>> +        if (virAsprintf(&path, "/proc/%llu/root/%s",
>> +                        (unsigned long long)ctrl->initpid,
>> +                        devs[i].path) < 0) {
>> +            virReportOOMError();
>> +            return -1;
>> +        }
>> +        dev_t dev = makedev(devs[i].maj, devs[i].min);
>> +        if (mknod(path, S_IFCHR, dev) < 0 ||
>> +            chmod(path, devs[i].mode)) {
>> +            virReportSystemError(errno,
>> +                                 _("Failed to make device %s"),
>> +                                 path);
>> +            VIR_FREE(path);
>> +            return -1;
>> +        }
>> +        VIR_FREE(path);
>> +    }
>> +
>> +    if (virAsprintf(&ptmx, "/proc/%llu/root/dev/pts/ptmx",
>> +                    (unsigned long long)ctrl->initpid) < 0) {
>> +        virReportOOMError();
>> +        return -1;
>> +    }
>> +
>> +    if (access(ptmx, W_OK)) {
>> +        char *path = NULL;
>> +        if (virAsprintf(&path, "/proc/%llu/root/dev/ptmx",
>> +                        (unsigned long long)ctrl->initpid) < 0) {
>> +            virReportOOMError();
>> +            VIR_FREE(ptmx);
>> +            return -1;
>> +        }
>> +        /* Legacy devpts, so we need to just use shared one */
>> +        dev_t dev = makedev(LXC_DEV_MAJ_TTY, LXC_DEV_MIN_PTMX);
>> +        if (mknod(path, S_IFCHR, dev) < 0 ||
>> +            chmod(path, 0666)) {
>> +            virReportSystemError(errno,
>> +                                 _("Failed to make device %s"), path);
>> +            VIR_FREE(path);
>> +            VIR_FREE(ptmx);
>> +            return -1;
>> +        }
>> +        VIR_FREE(path);
>> +    }
>> +    VIR_FREE(ptmx);
>> +    return 0;
>> +}
>> +
>> +
>>  /**
>>   * virLXCControllerMoveInterfaces
>>   * @nveths: number of interfaces
>> @@ -1535,6 +1608,16 @@ virLXCControllerRun(virLXCControllerPtr ctrl)
>>          goto cleanup;
>>      }
>>  
>> +    /* Populate devices for container */
>> +    if (virLXCControllerPopulateDevices(ctrl) < 0)
>> +        goto cleanup;
> 
> We ought to be able to invoke this before lxcContainerStart, so
> that we can avoid the send/wait continue bit
> 

We have to wait for init task of container running.
So we can populate devices at the right placement.


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