diff options
Diffstat (limited to 'security')
| -rw-r--r-- | security/device_cgroup.c | 202 |
1 files changed, 159 insertions, 43 deletions
diff --git a/security/device_cgroup.c b/security/device_cgroup.c index 8365909f5f8c..9134dbf70d3e 100644 --- a/security/device_cgroup.c +++ b/security/device_cgroup.c @@ -306,57 +306,138 @@ static int devcgroup_seq_show(struct seq_file *m, void *v) } /** - * may_access - verifies if a new exception is part of what is allowed - * by a dev cgroup based on the default policy + - * exceptions. This is used to make sure a child cgroup - * won't have more privileges than its parent or to - * verify if a certain access is allowed. - * @dev_cgroup: dev cgroup to be tested against - * @refex: new exception - * @behavior: behavior of the exception + * match_exception - iterates the exception list trying to find a complete match + * @exceptions: list of exceptions + * @type: device type (DEV_BLOCK or DEV_CHAR) + * @major: device file major number, ~0 to match all + * @minor: device file minor number, ~0 to match all + * @access: permission mask (ACC_READ, ACC_WRITE, ACC_MKNOD) + * + * It is considered a complete match if an exception is found that will + * contain the entire range of provided parameters. + * + * Return: true in case it matches an exception completely */ -static bool may_access(struct dev_cgroup *dev_cgroup, - struct dev_exception_item *refex, - enum devcg_behavior behavior) +static bool match_exception(struct list_head *exceptions, short type, + u32 major, u32 minor, short access) { struct dev_exception_item *ex; - bool match = false; - rcu_lockdep_assert(rcu_read_lock_held() || - lockdep_is_held(&devcgroup_mutex), - "device_cgroup::may_access() called without proper synchronization"); + list_for_each_entry_rcu(ex, exceptions, list) { + if ((type & DEV_BLOCK) && !(ex->type & DEV_BLOCK)) + continue; + if ((type & DEV_CHAR) && !(ex->type & DEV_CHAR)) + continue; + if (ex->major != ~0 && ex->major != major) + continue; + if (ex->minor != ~0 && ex->minor != minor) + continue; + /* provided access cannot have more than the exception rule */ + if (access & (~ex->access)) + continue; + return true; + } + return false; +} + +/** + * match_exception_partial - iterates the exception list trying to find a partial match + * @exceptions: list of exceptions + * @type: device type (DEV_BLOCK or DEV_CHAR) + * @major: device file major number, ~0 to match all + * @minor: device file minor number, ~0 to match all + * @access: permission mask (ACC_READ, ACC_WRITE, ACC_MKNOD) + * + * It is considered a partial match if an exception's range is found to + * contain *any* of the devices specified by provided parameters. This is + * used to make sure no extra access is being granted that is forbidden by + * any of the exception list. + * + * Return: true in case the provided range mat matches an exception completely + */ +static bool match_exception_partial(struct list_head *exceptions, short type, + u32 major, u32 minor, short access) +{ + struct dev_exception_item *ex; - list_for_each_entry_rcu(ex, &dev_cgroup->exceptions, list) { - if ((refex->type & DEV_BLOCK) && !(ex->type & DEV_BLOCK)) + list_for_each_entry_rcu(ex, exceptions, list) { + if ((type & DEV_BLOCK) && !(ex->type & DEV_BLOCK)) continue; - if ((refex->type & DEV_CHAR) && !(ex->type & DEV_CHAR)) + if ((type & DEV_CHAR) && !(ex->type & DEV_CHAR)) continue; - if (ex->major != ~0 && ex->major != refex->major) + /* + * We must be sure that both the exception and the provided + * range aren't masking all devices + */ + if (ex->major != ~0 && major != ~0 && ex->major != major) continue; - if (ex->minor != ~0 && ex->minor != refex->minor) + if (ex->minor != ~0 && minor != ~0 && ex->minor != minor) continue; - if (refex->access & (~ex->access)) + /* + * In order to make sure the provided range isn't matching + * an exception, all its access bits shouldn't match the + * exception's access bits + */ + if (!(access & ex->access)) continue; - match = true; - break; + return true; } + return false; +} + +/** + * verify_new_ex - verifies if a new exception is allowed by parent cgroup's permissions + * @dev_cgroup: dev cgroup to be tested against + * @refex: new exception + * @behavior: behavior of the exception's dev_cgroup + * + * This is used to make sure a child cgroup won't have more privileges + * than its parent + */ +static bool verify_new_ex(struct dev_cgroup *dev_cgroup, + struct dev_exception_item *refex, + enum devcg_behavior behavior) +{ + bool match = false; + + rcu_lockdep_assert(rcu_read_lock_held() || + lockdep_is_held(&devcgroup_mutex), + "device_cgroup:verify_new_ex called without proper synchronization"); if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW) { if (behavior == DEVCG_DEFAULT_ALLOW) { - /* the exception will deny access to certain devices */ + /* + * new exception in the child doesn't matter, only + * adding extra restrictions + */ return true; } else { - /* the exception will allow access to certain devices */ + /* + * new exception in the child will add more devices + * that can be acessed, so it can't match any of + * parent's exceptions, even slightly + */ + match = match_exception_partial(&dev_cgroup->exceptions, + refex->type, + refex->major, + refex->minor, + refex->access); + 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 */ + /* + * Only behavior == DEVCG_DEFAULT_DENY allowed here, therefore + * the new exception will add access to more devices and must + * be contained completely in an parent's exception to be + * allowed + */ + match = match_exception(&dev_cgroup->exceptions, refex->type, + refex->major, refex->minor, + refex->access); + if (match) /* parent has an exception that matches the proposed */ return true; @@ -378,7 +459,38 @@ static int parent_has_perm(struct dev_cgroup *childcg, if (!parent) return 1; - return may_access(parent, ex, childcg->behavior); + return verify_new_ex(parent, ex, childcg->behavior); +} + +/** + * parent_allows_removal - verify if it's ok to remove an exception + * @childcg: child cgroup from where the exception will be removed + * @ex: exception being removed + * + * When removing an exception in cgroups with default ALLOW policy, it must + * be checked if removing it will give the child cgroup more access than the + * parent. + * + * Return: true if it's ok to remove exception, false otherwise + */ +static bool parent_allows_removal(struct dev_cgroup *childcg, + struct dev_exception_item *ex) +{ + struct dev_cgroup *parent = css_to_devcgroup(css_parent(&childcg->css)); + + if (!parent) + return true; + + /* It's always allowed to remove access to devices */ + if (childcg->behavior == DEVCG_DEFAULT_DENY) + return true; + + /* + * Make sure you're not removing part or a whole exception existing in + * the parent cgroup + */ + return !match_exception_partial(&parent->exceptions, ex->type, + ex->major, ex->minor, ex->access); } /** @@ -616,17 +728,21 @@ static int devcgroup_update_access(struct dev_cgroup *devcgroup, switch (filetype) { case DEVCG_ALLOW: - if (!parent_has_perm(devcgroup, &ex)) - return -EPERM; /* * If the default policy is to allow 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_ALLOW) { + /* Check if the parent allows removing it first */ + if (!parent_allows_removal(devcgroup, &ex)) + return -EPERM; dev_exception_rm(devcgroup, &ex); - return 0; + break; } + + if (!parent_has_perm(devcgroup, &ex)) + return -EPERM; rc = dev_exception_add(devcgroup, &ex); break; case DEVCG_DENY: @@ -704,18 +820,18 @@ static int __devcgroup_check_permission(short type, u32 major, u32 minor, short access) { struct dev_cgroup *dev_cgroup; - struct dev_exception_item ex; - int rc; - - memset(&ex, 0, sizeof(ex)); - ex.type = type; - ex.major = major; - ex.minor = minor; - ex.access = access; + bool rc; rcu_read_lock(); dev_cgroup = task_devcgroup(current); - rc = may_access(dev_cgroup, &ex, dev_cgroup->behavior); + if (dev_cgroup->behavior == DEVCG_DEFAULT_ALLOW) + /* Can't match any of the exceptions, even partially */ + rc = !match_exception_partial(&dev_cgroup->exceptions, + type, major, minor, access); + else + /* Need to match completely one exception to be allowed */ + rc = match_exception(&dev_cgroup->exceptions, type, major, + minor, access); rcu_read_unlock(); if (!rc) |