devcg: prepare may_access() for hierarchy support
Currently may_access() is only able to verify if an exception is valid for the
current cgroup, which has the same behavior. With hierarchy, it'll be also used
to verify if a cgroup local exception is valid towards its cgroup parent, which
might have different behavior.
v2:
- updated patch description
- rebased on top of a new patch to expand the may_access() logic to make it
more clear
- fixed argument description order in may_access()
Acked-by: Tejun Heo <tj@kernel.org>
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: Aristeu Rozanski <aris@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
diff --git a/security/device_cgroup.c b/security/device_cgroup.c
index 4ad55a9..ddf3c70 100644
--- a/security/device_cgroup.c
+++ b/security/device_cgroup.c
@@ -25,6 +25,12 @@
static DEFINE_MUTEX(devcgroup_mutex);
+enum devcg_behavior {
+ DEVCG_DEFAULT_NONE,
+ DEVCG_DEFAULT_ALLOW,
+ DEVCG_DEFAULT_DENY,
+};
+
/*
* exception list locking rules:
* hold devcgroup_mutex for update/read.
@@ -42,10 +48,7 @@
struct dev_cgroup {
struct cgroup_subsys_state css;
struct list_head exceptions;
- enum {
- DEVCG_DEFAULT_ALLOW,
- DEVCG_DEFAULT_DENY,
- } behavior;
+ enum devcg_behavior behavior;
};
static inline struct dev_cgroup *css_to_devcgroup(struct cgroup_subsys_state *s)
@@ -304,9 +307,11 @@
* verify if a certain access is allowed.
* @dev_cgroup: dev cgroup to be tested against
* @refex: new exception
+ * @behavior: behavior of the exception
*/
static bool may_access(struct dev_cgroup *dev_cgroup,
- struct dev_exception_item *refex)
+ struct dev_exception_item *refex,
+ enum devcg_behavior behavior)
{
struct dev_exception_item *ex;
bool match = false;
@@ -330,19 +335,27 @@
break;
}
- /*
- * In two cases we'll consider this new exception valid:
- * - the dev cgroup has its default policy to deny + exception list:
- * the new exception *should* match the exceptions
- * - the dev cgroup has its default policy to allow + exception list:
- * the new exception should *not* match any of the exceptions
- */
- if (dev_cgroup->behavior == DEVCG_DEFAULT_DENY) {
- if (match)
+ if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW) {
+ if (behavior == DEVCG_DEFAULT_ALLOW) {
+ /* the exception will deny access to certain devices */
return true;
+ } else {
+ /* the exception will allow access to certain devices */
+ if (match)
+ /*
+ * a new exception allowing access shouldn't
+ * match an parent's exception
+ */
+ return false;
+ return true;
+ }
} else {
- if (!match)
+ /* only behavior == DEVCG_DEFAULT_DENY allowed here */
+ if (match)
+ /* parent has an exception that matches the proposed */
return true;
+ else
+ return false;
}
return false;
}
@@ -361,7 +374,7 @@
if (!pcg)
return 1;
parent = cgroup_to_devcgroup(pcg);
- return may_access(parent, ex);
+ return may_access(parent, ex, childcg->behavior);
}
/**
@@ -395,7 +408,7 @@
{
const char *b;
char temp[12]; /* 11 + 1 characters needed for a u32 */
- int count, rc;
+ int count, rc = 0;
struct dev_exception_item ex;
struct cgroup *p = devcgroup->css.cgroup;
struct dev_cgroup *parent = NULL;
@@ -612,7 +625,7 @@
rcu_read_lock();
dev_cgroup = task_devcgroup(current);
- rc = may_access(dev_cgroup, &ex);
+ rc = may_access(dev_cgroup, &ex, dev_cgroup->behavior);
rcu_read_unlock();
if (!rc)