Difference between revisions of "Security"

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(Some datails about global CAPs we need in criu)
(not needed anymore)
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CRIU has security issues when working with [[Userns|user namespaces]] and [[selinux]]
 
CRIU has security issues when working with [[Userns|user namespaces]] and [[selinux]]
 
== Kernel restrictions ==
 
 
Currently there are a few places in the kernel which test for action preformed being allowed for capable users only:
 
 
* Reading of <code>/proc/$pid/map_files</code> entries is guarded by <code>CAP_SYS_ADMIN</code>. This data is intensively used by CRIU on the dump.
 
* Restoring memory maps with <code>prctl</code> may require <code>CAP_SYS_RESOURCE</code> on old CRIU versions which don't use <code>PR_SET_MM_MAP</code> interface.
 
* Upon CRIU start it might try to load net-diag modules which require <code>CAP_SYS_MODULE</code>.
 
  
 
== Code example ==
 
== Code example ==

Revision as of 16:41, 14 September 2015

Due to restrictions imposed by several kernel APIs CRIU uses, the tools can only work with run with root privileges. However, if the node administrator sets the +suid bit on the criu binary, or runs criu as an RPC service, criu will be able to work on behalf of regular user.

In the latter case, the following security restrictions would apply:

Legend:
cr_*   -- ids of the calling user;
others -- ids of process that we're trying to dump/restore;
  • criu will refuse to dump/restore process if [se]?uid is not equal to cr_uid
  • criu will refuse to dump/restore process if [se]?gid is not equal to cr_gid or cr_groups do not contain it
  • criu will refuse to restore process if cr_groups don't contain groups
  • criu will refuse to dump/restore any bits set in any capability set

See also

CRIU has security issues when working with user namespaces and selinux

Code example

Here is a simplified version of code from security.c.

bool check_uids()
{
	if (cr_uid == 0)
		return true;

	if (cr_uid == ruid && cr_uid == suid && cr_uid == eid)
		return true;

	return false;
}

bool check_gids()
{
	if (cr_gid == 0)
		return true;

	if ((contains(cr_groups, rgid) || cr_gid == rgid) &&
	    (contains(cr_groups, egid) || cr_gid == egid) &&
	    (contains(cr_groups, sgid) || cr_gid == sgid))
		return true;

	return false;
}

/*
 * There is no need to check groups on dump, because if uids and gids match
 * then groups will match too. Btw, getting groups on dump is problematic.
 * We can't parse proc, as it contains only first 32 groups. And we can't use
 * getgrouplist, as it reads /etc/group which depends on the namespace.
 *
 * On restore we're getting groups from imgs and can check if user didn't add
 * wrong groups by modifying images.
 */
bool check_groups()
{
	if (cr_gid == 0)
		return true;

	for (i = 0; i < ngroups; ++i) {
		if (!contains(cr_groups, groups[i]))
			return false;
	}

	return true;
}

bool check_caps()
{
	/*
	 * Impose the most strict requirements for now.
	 * "Real" root user can use any caps, other users may
	 * use none. Later we will implement more sophisticated
	 * security model.
	 */

	if (cr_uid == 0 && cr_gid == 0)
		return true;

	for (i = 0; i < CR_CAP_SIZE; i++) {
		if (inh[i] != 0 || eff[i] != 0 || prm[i] != 0)
			return false;
	}

	return true;
}

bool may_dump()
{
	return  check_uids() &&
		check_gids() &&
		check_caps();
}

bool may_restore()
{
	return  check_uids() &&
		check_gids() &&
		check_groups() &&
		check_caps();
}