device_cgroup: add proper checking when changing default behavior
Before changing a group's default behavior to ALLOW, we must check if
its parent's behavior is also ALLOW.
Signed-off-by: Aristeu Rozanski <aris@redhat.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Li Zefan <lizefan@huawei.com>
Cc: James Morris <jmorris@namei.org>
Cc: Pavel Emelyanov <xemul@openvz.org>
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Cc: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/security/device_cgroup.c b/security/device_cgroup.c
index 4fbae8d..842c254 100644
--- a/security/device_cgroup.c
+++ b/security/device_cgroup.c
@@ -344,6 +344,17 @@
return may_access(parent, ex);
}
+/**
+ * may_allow_all - checks if it's possible to change the behavior to
+ * allow based on parent's rules.
+ * @parent: device cgroup's parent
+ * returns: != 0 in case it's allowed, 0 otherwise
+ */
+static inline int may_allow_all(struct dev_cgroup *parent)
+{
+ return parent->behavior == DEVCG_DEFAULT_ALLOW;
+}
+
/*
* Modify the exception list using allow/deny rules.
* CAP_SYS_ADMIN is needed for this. It's at least separate from CAP_MKNOD
@@ -364,6 +375,8 @@
char temp[12]; /* 11 + 1 characters needed for a u32 */
int count, rc;
struct dev_exception_item ex;
+ struct cgroup *p = devcgroup->css.cgroup;
+ struct dev_cgroup *parent = cgroup_to_devcgroup(p->parent);
if (!capable(CAP_SYS_ADMIN))
return -EPERM;
@@ -375,9 +388,13 @@
case 'a':
switch (filetype) {
case DEVCG_ALLOW:
- if (!parent_has_perm(devcgroup, &ex))
+ if (!may_allow_all(parent))
return -EPERM;
dev_exception_clean(devcgroup);
+ rc = dev_exceptions_copy(&devcgroup->exceptions,
+ &parent->exceptions);
+ if (rc)
+ return rc;
devcgroup->behavior = DEVCG_DEFAULT_ALLOW;
break;
case DEVCG_DENY: