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Re: [libvirt] [PATCH v2]LXC: Helper function for checking ownership of dir when userns enabled



On Fri, Aug 09, 2013 at 04:05:58PM +0800, Chen Hanxiao wrote:
> From: Chen Hanxiao <chenhanxiao cn fujitsu com>
> 
> If we enable userns, the ownership of dir we provided for containers
> should match the uid/gid in idmap.
> Currently, the debug log is very implicit or misleading sometimes.
> This patch will help clarify this for us when using
> debug log or virsh.
> 
> v2: syntax-check clean
> 
> Signed-off-by: Chen Hanxiao <chenhanxiao cn fujitsu com>
> ---
>  src/lxc/lxc_container.c |   46 ++++++++++++++++++++++++++++++++++++++++++++++
>  1 files changed, 46 insertions(+), 0 deletions(-)
> 
> diff --git a/src/lxc/lxc_container.c b/src/lxc/lxc_container.c
> index b910b10..2ccdc61 100644
> --- a/src/lxc/lxc_container.c
> +++ b/src/lxc/lxc_container.c
> @@ -1815,6 +1815,49 @@ lxcNeedNetworkNamespace(virDomainDefPtr def)
>      return false;
>  }
>  
> +/*
> + * Helper function for helping check
> + * whether we have enough privilege
> + * to operate the source dir when userns enabled
> + * @vmDef: pointer to vm definition structure
> + * Returns 0 on success or -1 in case of error
> + */
> +static int
> +lxcContainerUsernsSrcOwnershipCheck(virDomainDefPtr vmDef)
> +{
> +    struct stat buf;
> +    size_t i;
> +    uid_t uid;
> +    gid_t gid;
> +
> +    VIR_DEBUG("vmDef->nfss %d", (int)vmDef->nfss);
> +    for (i = 0; i < vmDef->nfss; i++) {
> +        VIR_DEBUG("dst is %s, src is %s",
> +                  vmDef->fss[i]->dst,
> +                  vmDef->fss[i]->src);
> +
> +        uid = vmDef->idmap.uidmap[0].target;
> +        gid = vmDef->idmap.gidmap[0].target;
> +
> +        if (lstat(vmDef->fss[i]->src, &buf) < 0) {
> +            virReportSystemError(errno, _("Cannot access '%s'"),
> +                                 vmDef->fss[i]->src);
> +            return -1;
> +        } else if (uid != buf.st_uid || gid != buf.st_gid) {

Comparing the uid/gid owner of a file is not an accurate check.
For example, a file could have ACLs set which allow access even
when the uid/gid do not match.

I think we should focus on improving the error messages  reported
when we hit the actual problem rather than trying to pre-guess the
problem and potentially get it wrong.

Daniel
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