From 64e104771351d365e51e588a0e9a656ae6ed2f50 Mon Sep 17 00:00:00 2001 From: Aristeu Rozanski Date: Tue, 6 Nov 2012 07:25:04 -0800 Subject: [PATCH 1/2] device_cgroup: fix unchecked cgroup parent usage In 4cef7299b478687 ("device_cgroup: add proper checking when changing default behavior") the cgroup parent usage is unchecked. root will not have a parent and trying to use device.{allow,deny} will cause problems. For some reason my stressing scripts didn't test the root directory so I didn't catch it on my regular tests. Signed-off-by: Aristeu Rozanski Cc: Li Zefan Cc: James Morris Cc: Pavel Emelyanov Acked-by: Serge E. Hallyn Cc: Jiri Slaby Cc: Tejun Heo Signed-off-by: Tejun Heo --- security/device_cgroup.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/security/device_cgroup.c b/security/device_cgroup.c index 842c254396db..96d87eab1660 100644 --- a/security/device_cgroup.c +++ b/security/device_cgroup.c @@ -352,6 +352,8 @@ static int parent_has_perm(struct dev_cgroup *childcg, */ static inline int may_allow_all(struct dev_cgroup *parent) { + if (!parent) + return 1; return parent->behavior == DEVCG_DEFAULT_ALLOW; } @@ -376,11 +378,14 @@ static int devcgroup_update_access(struct dev_cgroup *devcgroup, int count, rc; struct dev_exception_item ex; struct cgroup *p = devcgroup->css.cgroup; - struct dev_cgroup *parent = cgroup_to_devcgroup(p->parent); + struct dev_cgroup *parent = NULL; if (!capable(CAP_SYS_ADMIN)) return -EPERM; + if (p->parent) + parent = cgroup_to_devcgroup(p->parent); + memset(&ex, 0, sizeof(ex)); b = buffer; @@ -391,11 +396,14 @@ static int devcgroup_update_access(struct dev_cgroup *devcgroup, if (!may_allow_all(parent)) return -EPERM; dev_exception_clean(devcgroup); + devcgroup->behavior = DEVCG_DEFAULT_ALLOW; + if (!parent) + break; + rc = dev_exceptions_copy(&devcgroup->exceptions, &parent->exceptions); if (rc) return rc; - devcgroup->behavior = DEVCG_DEFAULT_ALLOW; break; case DEVCG_DENY: dev_exception_clean(devcgroup); From 201e72acb2d3821e2de9ce6091e98859c316b29a Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Tue, 6 Nov 2012 09:17:37 -0800 Subject: [PATCH 2/2] device_cgroup: fix RCU usage dev_cgroup->exceptions is protected with devcgroup_mutex for writes and RCU for reads; however, RCU usage isn't correct. * dev_exception_clean() doesn't use RCU variant of list_del() and kfree(). The function can race with may_access() and may_access() may end up dereferencing already freed memory. Use list_del_rcu() and kfree_rcu() instead. * may_access() may be called only with RCU read locked but doesn't use RCU safe traversal over ->exceptions. Use list_for_each_entry_rcu(). Signed-off-by: Tejun Heo Acked-by: Serge E. Hallyn Cc: stable@vger.kernel.org Cc: Aristeu Rozanski Cc: Li Zefan --- security/device_cgroup.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/security/device_cgroup.c b/security/device_cgroup.c index 96d87eab1660..b08d20c66c2e 100644 --- a/security/device_cgroup.c +++ b/security/device_cgroup.c @@ -164,8 +164,8 @@ static void dev_exception_clean(struct dev_cgroup *dev_cgroup) struct dev_exception_item *ex, *tmp; list_for_each_entry_safe(ex, tmp, &dev_cgroup->exceptions, list) { - list_del(&ex->list); - kfree(ex); + list_del_rcu(&ex->list); + kfree_rcu(ex, rcu); } } @@ -298,7 +298,7 @@ static int may_access(struct dev_cgroup *dev_cgroup, struct dev_exception_item *ex; bool match = false; - list_for_each_entry(ex, &dev_cgroup->exceptions, list) { + list_for_each_entry_rcu(ex, &dev_cgroup->exceptions, list) { if ((refex->type & DEV_BLOCK) && !(ex->type & DEV_BLOCK)) continue; if ((refex->type & DEV_CHAR) && !(ex->type & DEV_CHAR))