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Re: [libvirt] [PATCH 1/1] lxc: only do CLONE_NEWUSER when kernel supports it



On Fri, Apr 17, 2009 at 04:50:10PM -0500, Serge E. Hallyn wrote:
> >From 2513f8a7e0654e84570fe0ef2204dabe276b9e4e Mon Sep 17 00:00:00 2001
> From: root <root jaunty (none)>
> Date: Fri, 17 Apr 2009 16:41:01 -0500
> Subject: [PATCH 1/1] lxc: only do CLONE_NEWUSER when kernel supports it
> 
> The ubuntu jaunty kernel is not compiled with USER_NS.  Since
> libvirt-lxc always does clone(CLONE_NEWUSER) it gets -EINVAL
> and mysteriously claims to be unable to contact hypervisor.
> 
> This patch isn't the right thing to do, but I'm not sure what
> is.  User namespaces do (since recently) isolate the in-kernel
> keyring.  So the right thing might be to add a flag to the
> xml definition file to specify whether to use a user namespace.
> This patch doesn't do that, rather it always does CLONE_NEWUSER
> if the kernel supports it, and never if not.

I think this patch is sufficient. If it is genuinely important to
support CLONE_NEWUSER then Ubuntu can fix their kernel config,
otherwise simply disabling it in libvirt when not present is fine.

> diff --git a/src/lxc_container.c b/src/lxc_container.c
> index 67c66bd..8069af7 100644
> --- a/src/lxc_container.c
> +++ b/src/lxc_container.c
> @@ -666,6 +666,11 @@ static int lxcContainerChild( void *data )
>      return lxcContainerExecInit(vmDef);
>  }
>  
> +int userns_supported(void)
> +{
> +	return lxcContainerAvailable(LXC_CONTAINER_FEATURE_USER) == 0;
> +}
> +
>  /**
>   * lxcContainerStart:
>   * @driver: pointer to driver structure
> @@ -694,7 +699,10 @@ int lxcContainerStart(virDomainDefPtr def,
>      }
>      stacktop = stack + stacksize;
>  
> -    flags = CLONE_NEWPID|CLONE_NEWNS|CLONE_NEWUTS|CLONE_NEWUSER|CLONE_NEWIPC|SIGCHLD;
> +    flags = CLONE_NEWPID|CLONE_NEWNS|CLONE_NEWUTS|CLONE_NEWIPC|SIGCHLD;
> +
> +    if (userns_supported())
> +        flags |= CLONE_NEWUSER;
>  
>      if (def->nets != NULL)
>          flags |= CLONE_NEWNET;
> @@ -719,13 +727,16 @@ static int lxcContainerDummyChild(void *argv ATTRIBUTE_UNUSED)
>  
>  int lxcContainerAvailable(int features)
>  {
> -    int flags = CLONE_NEWPID|CLONE_NEWNS|CLONE_NEWUTS|CLONE_NEWUSER|
> +    int flags = CLONE_NEWPID|CLONE_NEWNS|CLONE_NEWUTS|
>          CLONE_NEWIPC|SIGCHLD;
>      int cpid;
>      char *childStack;
>      char *stack;
>      int childStatus;
>  
> +    if (features & LXC_CONTAINER_FEATURE_USER)
> +        flags |= CLONE_NEWUSER;
> +
>      if (features & LXC_CONTAINER_FEATURE_NET)
>          flags |= CLONE_NEWNET;
>  
> diff --git a/src/lxc_container.h b/src/lxc_container.h
> index 5d037b0..b99e83e 100644
> --- a/src/lxc_container.h
> +++ b/src/lxc_container.h
> @@ -28,6 +28,7 @@
>  
>  enum {
>      LXC_CONTAINER_FEATURE_NET = (1 << 0),
> +    LXC_CONTAINER_FEATURE_USER = (1 << 1),
>  };
>  
>  #define LXC_DEV_MAJ_MEMORY  1

ACK


Daniel
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