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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>
This commit is contained in:
Aristeu Rozanski 2013-02-15 11:55:45 -05:00 committed by Tejun Heo
parent 26898fdff3
commit c39a2a3018
1 changed files with 31 additions and 18 deletions
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49
security/device_cgroup.c
View File

@ -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_exception_item {
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 @@ static int devcgroup_seq_read(struct cgroup *cgroup, struct cftype *cft,
* 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 @@ static bool may_access(struct dev_cgroup *dev_cgroup,
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 @@ static int parent_has_perm(struct dev_cgroup *childcg,
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 @@ static int devcgroup_update_access(struct dev_cgroup *devcgroup,
{
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 @@ static int __devcgroup_check_permission(short type, u32 major, u32 minor,
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)