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 <[email protected]> Acked-by: Serge Hallyn <[email protected]> Cc: Tejun Heo <[email protected]> Cc: Serge Hallyn <[email protected]> Signed-off-by: Aristeu Rozanski <[email protected]> --- security/device_cgroup.c | 49 +++++++++++++++++++++++++++++------------------ 1 file changed, 31 insertions(+), 18 deletions(-) --- github.orig/security/device_cgroup.c 2013-02-14 10:47:12.146177936 -0500 +++ github/security/device_cgroup.c 2013-02-14 10:47:12.411181646 -0500 @@ -25,6 +25,12 @@ * Copyright 2007 IBM Corp 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) @@ -301,9 +304,11 @@ return 0; * 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; @@ -327,19 +332,27 @@ if (ex->minor != ~0 && ex->minor != re 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; } @@ -358,7 +371,7 @@ static int parent_has_perm(struct dev_cg if (!pcg) return 1; parent = cgroup_to_devcgroup(pcg); - return may_access(parent, ex); + return may_access(parent, ex, childcg->behavior); } /** @@ -392,7 +405,7 @@ static int devcgroup_update_access(struc { 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; @@ -609,7 +622,7 @@ memset(&ex, 0, sizeof(ex)); 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) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
