[libvirt] [RFC][PATCH] lxc: drop CAP_SYS_BOOT capability to preventrebooting from inside containers

[Ryota Ozaki]

Hi Serge,

On Fri, May 8, 2009 at 9:12 AM, Serge E. Hallyn <serue at us.ibm.com> wrote:
> Quoting Ryota Ozaki (ozaki.ryota at gmail.com):
>> Hi,
>>
>> Current lxc driver unexpectedly allows users inside containers to reboot
>> host physical machine. This patch prevents this by dropping CAP_SYS_BOOT
>> capability in the bounding set of the init processes in every containers.
>>
>> Note that the patch intends to make it easy to add further capabilities
>> to drop if needed, although I'm not sure which capabilities should be
>> dropped. (We might need to drop CAP_SETFCAP as well to be strict...)
>>
>> Thanks,
>>   ozaki-r
>>
>> Signed-off-by: Ryota Ozaki <ozaki.ryota at gmail.com>
>>
>> >From 0e7a7622bc6411bbe76c05c63c6e6e61d379d97b Mon Sep 17 00:00:00 2001
>> From: Ryota Ozaki <ozaki.ryota at gmail.com>
>> Date: Fri, 8 May 2009 04:29:24 +0900
>> Subject: [PATCH] lxc: drop CAP_SYS_BOOT capability to prevent
>> rebooting from inside containers
>>
>> Current lxc driver unexpectedly allows users inside containers to reboot
>> host physical machine. This patch prevents this by dropping CAP_SYS_BOOT
>> capability in the bounding set of the init processes in every containers.
>> ---
>>  src/lxc_container.c |   30 ++++++++++++++++++++++++++++++
>>  1 files changed, 30 insertions(+), 0 deletions(-)
>>
>> diff --git a/src/lxc_container.c b/src/lxc_container.c
>> index 3946b84..37ab216 100644
>> --- a/src/lxc_container.c
>> +++ b/src/lxc_container.c
>> @@ -32,6 +32,8 @@
>>  #include <sys/ioctl.h>
>>  #include <sys/mount.h>
>>  #include <sys/wait.h>
>> +#include <sys/prctl.h>
>> +#include <sys/capability.h>
>>  #include <unistd.h>
>>  #include <mntent.h>
>>
>> @@ -639,6 +641,30 @@ static int lxcContainerSetupMounts(virDomainDefPtr vmDef,
>>          return lxcContainerSetupExtraMounts(vmDef);
>>  }
>>
>> +
>> +static int lxcContainerDropCapabilities( virDomainDefPtr vmDef )
>> +{
>> +    int i;
>> +    const struct {
>> +        int id;
>> +        const char *name;
>> +    } caps[] = {
>> +#define ID_STRING(name) name, #name
>> +        { ID_STRING(CAP_SYS_BOOT) },
>> +    };
>> +
>> +    for (i = 0 ; i < ARRAY_CARDINALITY(caps) ; i++) {
>> +        if (prctl(PR_CAPBSET_DROP, caps[i].id, 0, 0, 0)) {
>> +            lxcError(NULL, NULL, VIR_ERR_INTERNAL_ERROR,
>> +                     "%s", _("failed to drop %s"), caps[i].name);
>> +            return -1;
>
> Ideally you should also drop it from pI.

If not drop it, a user in a container could set CAP_SYS_BOOT fI bit of
/bin/reboot on and then the user could gain CAP_SYS_BOOT back through
the fI. Is this understanding right?

Thanks,
  ozaki-r

>
>> +        }
>> +    }
>> +
>> +    return 0;
>> +}
>> +
>> +
>>  /**
>>   * lxcChild:
>>   * @argv: Pointer to container arguments
>> @@ -705,6 +731,10 @@ static int lxcContainerChild( void *data )
>>      if (lxcContainerEnableInterfaces(argv->nveths, argv->veths) < 0)
>>          return -1;
>>
>> +    /* drop a set of root capabilities */
>> +    if (lxcContainerDropCapabilities(vmDef) < 0)
>> +        return -1;
>> +
>>      /* this function will only return if an error occured */
>>      return lxcContainerExecInit(vmDef);
>>  }
>> --
>> 1.6.0.6
>>
>> --
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>