diff options
Diffstat (limited to 'security/device_cgroup.c')
| -rw-r--r-- | security/device_cgroup.c | 267 |
1 files changed, 211 insertions, 56 deletions
diff --git a/security/device_cgroup.c b/security/device_cgroup.c index 1c69e38e3a2c..dd0dc574d78d 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 +48,9 @@ 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; + /* temporary list for pending propagation operations */ + struct list_head propagate_pending; }; static inline struct dev_cgroup *css_to_devcgroup(struct cgroup_subsys_state *s) @@ -182,35 +187,62 @@ static void dev_exception_clean(struct dev_cgroup *dev_cgroup) __dev_exception_clean(dev_cgroup); } +static inline bool is_devcg_online(const struct dev_cgroup *devcg) +{ + return (devcg->behavior != DEVCG_DEFAULT_NONE); +} + +/** + * devcgroup_online - initializes devcgroup's behavior and exceptions based on + * parent's + * @cgroup: cgroup getting online + * returns 0 in case of success, error code otherwise + */ +static int devcgroup_online(struct cgroup *cgroup) +{ + struct dev_cgroup *dev_cgroup, *parent_dev_cgroup = NULL; + int ret = 0; + + mutex_lock(&devcgroup_mutex); + dev_cgroup = cgroup_to_devcgroup(cgroup); + if (cgroup->parent) + parent_dev_cgroup = cgroup_to_devcgroup(cgroup->parent); + + if (parent_dev_cgroup == NULL) + dev_cgroup->behavior = DEVCG_DEFAULT_ALLOW; + else { + ret = dev_exceptions_copy(&dev_cgroup->exceptions, + &parent_dev_cgroup->exceptions); + if (!ret) + dev_cgroup->behavior = parent_dev_cgroup->behavior; + } + mutex_unlock(&devcgroup_mutex); + + return ret; +} + +static void devcgroup_offline(struct cgroup *cgroup) +{ + struct dev_cgroup *dev_cgroup = cgroup_to_devcgroup(cgroup); + + mutex_lock(&devcgroup_mutex); + dev_cgroup->behavior = DEVCG_DEFAULT_NONE; + mutex_unlock(&devcgroup_mutex); +} + /* * called from kernel/cgroup.c with cgroup_lock() held. */ static struct cgroup_subsys_state *devcgroup_css_alloc(struct cgroup *cgroup) { - struct dev_cgroup *dev_cgroup, *parent_dev_cgroup; - struct cgroup *parent_cgroup; - int ret; + struct dev_cgroup *dev_cgroup; dev_cgroup = kzalloc(sizeof(*dev_cgroup), GFP_KERNEL); if (!dev_cgroup) return ERR_PTR(-ENOMEM); INIT_LIST_HEAD(&dev_cgroup->exceptions); - parent_cgroup = cgroup->parent; - - if (parent_cgroup == NULL) - dev_cgroup->behavior = DEVCG_DEFAULT_ALLOW; - else { - parent_dev_cgroup = cgroup_to_devcgroup(parent_cgroup); - mutex_lock(&devcgroup_mutex); - ret = dev_exceptions_copy(&dev_cgroup->exceptions, - &parent_dev_cgroup->exceptions); - dev_cgroup->behavior = parent_dev_cgroup->behavior; - mutex_unlock(&devcgroup_mutex); - if (ret) { - kfree(dev_cgroup); - return ERR_PTR(ret); - } - } + INIT_LIST_HEAD(&dev_cgroup->propagate_pending); + dev_cgroup->behavior = DEVCG_DEFAULT_NONE; return &dev_cgroup->css; } @@ -304,9 +336,11 @@ 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 int may_access(struct dev_cgroup *dev_cgroup, - struct dev_exception_item *refex) +static bool may_access(struct dev_cgroup *dev_cgroup, + struct dev_exception_item *refex, + enum devcg_behavior behavior) { struct dev_exception_item *ex; bool match = false; @@ -330,18 +364,29 @@ static int 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 allow + exception list: - * the new exception should *not* match any of the exceptions - * (behavior == DEVCG_DEFAULT_ALLOW, !match) - * - the dev cgroup has its default policy to deny + exception list: - * the new exception *should* match the exceptions - * (behavior == DEVCG_DEFAULT_DENY, match) - */ - if ((dev_cgroup->behavior == DEVCG_DEFAULT_DENY) == match) - return 1; - return 0; + 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 { + /* only behavior == DEVCG_DEFAULT_DENY allowed here */ + if (match) + /* parent has an exception that matches the proposed */ + return true; + else + return false; + } + return false; } /* @@ -358,7 +403,7 @@ 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); } /** @@ -374,6 +419,111 @@ static inline int may_allow_all(struct dev_cgroup *parent) return parent->behavior == DEVCG_DEFAULT_ALLOW; } +/** + * revalidate_active_exceptions - walks through the active exception list and + * revalidates the exceptions based on parent's + * behavior and exceptions. The exceptions that + * are no longer valid will be removed. + * Called with devcgroup_mutex held. + * @devcg: cgroup which exceptions will be checked + * + * This is one of the three key functions for hierarchy implementation. + * This function is responsible for re-evaluating all the cgroup's active + * exceptions due to a parent's exception change. + * Refer to Documentation/cgroups/devices.txt for more details. + */ +static void revalidate_active_exceptions(struct dev_cgroup *devcg) +{ + struct dev_exception_item *ex; + struct list_head *this, *tmp; + + list_for_each_safe(this, tmp, &devcg->exceptions) { + ex = container_of(this, struct dev_exception_item, list); + if (!parent_has_perm(devcg, ex)) + dev_exception_rm(devcg, ex); + } +} + +/** + * get_online_devcg - walks the cgroup tree and fills a list with the online + * groups + * @root: cgroup used as starting point + * @online: list that will be filled with online groups + * + * Must be called with devcgroup_mutex held. Grabs RCU lock. + * Because devcgroup_mutex is held, no devcg will become online or offline + * during the tree walk (see devcgroup_online, devcgroup_offline) + * A separated list is needed because propagate_behavior() and + * propagate_exception() need to allocate memory and can block. + */ +static void get_online_devcg(struct cgroup *root, struct list_head *online) +{ + struct cgroup *pos; + struct dev_cgroup *devcg; + + lockdep_assert_held(&devcgroup_mutex); + + rcu_read_lock(); + cgroup_for_each_descendant_pre(pos, root) { + devcg = cgroup_to_devcgroup(pos); + if (is_devcg_online(devcg)) + list_add_tail(&devcg->propagate_pending, online); + } + rcu_read_unlock(); +} + +/** + * propagate_exception - propagates a new exception to the children + * @devcg_root: device cgroup that added a new exception + * @ex: new exception to be propagated + * + * returns: 0 in case of success, != 0 in case of error + */ +static int propagate_exception(struct dev_cgroup *devcg_root, + struct dev_exception_item *ex) +{ + struct cgroup *root = devcg_root->css.cgroup; + struct dev_cgroup *devcg, *parent, *tmp; + int rc = 0; + LIST_HEAD(pending); + + get_online_devcg(root, &pending); + + list_for_each_entry_safe(devcg, tmp, &pending, propagate_pending) { + parent = cgroup_to_devcgroup(devcg->css.cgroup->parent); + + /* + * in case both root's behavior and devcg is allow, a new + * restriction means adding to the exception list + */ + if (devcg_root->behavior == DEVCG_DEFAULT_ALLOW && + devcg->behavior == DEVCG_DEFAULT_ALLOW) { + rc = dev_exception_add(devcg, ex); + if (rc) + break; + } else { + /* + * in the other possible cases: + * root's behavior: allow, devcg's: deny + * root's behavior: deny, devcg's: deny + * the exception will be removed + */ + dev_exception_rm(devcg, ex); + } + revalidate_active_exceptions(devcg); + + list_del_init(&devcg->propagate_pending); + } + return rc; +} + +static inline bool has_children(struct dev_cgroup *devcgroup) +{ + struct cgroup *cgrp = devcgroup->css.cgroup; + + return !list_empty(&cgrp->children); +} + /* * Modify the exception list using allow/deny rules. * CAP_SYS_ADMIN is needed for this. It's at least separate from CAP_MKNOD @@ -392,7 +542,7 @@ 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; @@ -410,6 +560,9 @@ static int devcgroup_update_access(struct dev_cgroup *devcgroup, case 'a': switch (filetype) { case DEVCG_ALLOW: + if (has_children(devcgroup)) + return -EINVAL; + if (!may_allow_all(parent)) return -EPERM; dev_exception_clean(devcgroup); @@ -423,6 +576,9 @@ static int devcgroup_update_access(struct dev_cgroup *devcgroup, return rc; break; case DEVCG_DENY: + if (has_children(devcgroup)) + return -EINVAL; + dev_exception_clean(devcgroup); devcgroup->behavior = DEVCG_DEFAULT_DENY; break; @@ -517,22 +673,28 @@ static int devcgroup_update_access(struct dev_cgroup *devcgroup, dev_exception_rm(devcgroup, &ex); return 0; } - return dev_exception_add(devcgroup, &ex); + rc = dev_exception_add(devcgroup, &ex); + break; case DEVCG_DENY: /* * If the default policy is to deny by default, try to remove * an matching exception instead. And be silent about it: we * don't want to break compatibility */ - if (devcgroup->behavior == DEVCG_DEFAULT_DENY) { + if (devcgroup->behavior == DEVCG_DEFAULT_DENY) dev_exception_rm(devcgroup, &ex); - return 0; - } - return dev_exception_add(devcgroup, &ex); + else + rc = dev_exception_add(devcgroup, &ex); + + if (rc) + break; + /* we only propagate new restrictions */ + rc = propagate_exception(devcgroup, &ex); + break; default: - return -EINVAL; + rc = -EINVAL; } - return 0; + return rc; } static int devcgroup_access_write(struct cgroup *cgrp, struct cftype *cft, @@ -571,17 +733,10 @@ struct cgroup_subsys devices_subsys = { .can_attach = devcgroup_can_attach, .css_alloc = devcgroup_css_alloc, .css_free = devcgroup_css_free, + .css_online = devcgroup_online, + .css_offline = devcgroup_offline, .subsys_id = devices_subsys_id, .base_cftypes = dev_cgroup_files, - - /* - * While devices cgroup has the rudimentary hierarchy support which - * checks the parent's restriction, it doesn't properly propagates - * config changes in ancestors to their descendents. A child - * should only be allowed to add more restrictions to the parent's - * configuration. Fix it and remove the following. - */ - .broken_hierarchy = true, }; /** @@ -609,7 +764,7 @@ 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) |