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authorTejun Heo <tj@kernel.org>2013-12-06 15:07:32 -0500
committerTejun Heo <tj@kernel.org>2013-12-06 15:08:50 -0500
commit266ccd505e8acb98717819cef9d91d66c7b237cc (patch)
tree7c80dde5f9e6db5c216a8b262e9d098b92ea291b /kernel
parente605b36575e896edd8161534550c9ea021b03bc0 (diff)
downloadlinux-266ccd505e8acb98717819cef9d91d66c7b237cc.tar.bz2
cgroup: fix cgroup_create() error handling path
ae7f164a09 ("cgroup: move cgroup->subsys[] assignment to online_css()") moved cgroup->subsys[] assignements later in cgroup_create() but didn't update error handling path accordingly leading to the following oops and leaking later css's after an online_css() failure. The oops is from cgroup destruction path being invoked on the partially constructed cgroup which is not ready to handle empty slots in cgrp->subsys[] array. BUG: unable to handle kernel NULL pointer dereference at 0000000000000008 IP: [<ffffffff810eeaa8>] cgroup_destroy_locked+0x118/0x2f0 PGD a780a067 PUD aadbe067 PMD 0 Oops: 0000 [#1] SMP Modules linked in: CPU: 6 PID: 7360 Comm: mkdir Not tainted 3.13.0-rc2+ #69 Hardware name: task: ffff8800b9dbec00 ti: ffff8800a781a000 task.ti: ffff8800a781a000 RIP: 0010:[<ffffffff810eeaa8>] [<ffffffff810eeaa8>] cgroup_destroy_locked+0x118/0x2f0 RSP: 0018:ffff8800a781bd98 EFLAGS: 00010282 RAX: ffff880586903878 RBX: ffff880586903800 RCX: ffff880586903820 RDX: ffff880586903860 RSI: ffff8800a781bdb0 RDI: ffff880586903820 RBP: ffff8800a781bde8 R08: ffff88060e0b8048 R09: ffffffff811d7bc1 R10: 000000000000008c R11: 0000000000000001 R12: ffff8800a72286c0 R13: 0000000000000000 R14: ffffffff81cf7a40 R15: 0000000000000001 FS: 00007f60ecda57a0(0000) GS:ffff8806272c0000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000000000008 CR3: 00000000a7a03000 CR4: 00000000000007e0 Stack: ffff880586903860 ffff880586903910 ffff8800a72286c0 ffff880586903820 ffffffff81cf7a40 ffff880586903800 ffff88060e0b8018 ffffffff81cf7a40 ffff8800b9dbec00 ffff8800b9dbf098 ffff8800a781bec8 ffffffff810ef5bf Call Trace: [<ffffffff810ef5bf>] cgroup_mkdir+0x55f/0x5f0 [<ffffffff811c90ae>] vfs_mkdir+0xee/0x140 [<ffffffff811cb07e>] SyS_mkdirat+0x6e/0xf0 [<ffffffff811c6a19>] SyS_mkdir+0x19/0x20 [<ffffffff8169e569>] system_call_fastpath+0x16/0x1b This patch moves reference bumping inside online_css() loop, clears css_ar[] as css's are brought online successfully, and updates err_destroy path so that either a css is fully online and destroyed by cgroup_destroy_locked() or the error path frees it. This creates a duplicate css free logic in the error path but it will be cleaned up soon. v2: Li pointed out that cgroup_destroy_locked() would do NULL-deref if invoked with a cgroup which doesn't have all css's populated. Update cgroup_destroy_locked() so that it skips NULL css's. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Li Zefan <lizefan@huawei.com> Reported-by: Vladimir Davydov <vdavydov@parallels.com> Cc: stable@vger.kernel.org # v3.12+
Diffstat (limited to 'kernel')
-rw-r--r--kernel/cgroup.c31
1 files changed, 21 insertions, 10 deletions
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 8b729c278b64..bcb1755f410a 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4426,14 +4426,6 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
list_add_tail_rcu(&cgrp->sibling, &cgrp->parent->children);
root->number_of_cgroups++;
- /* each css holds a ref to the cgroup's dentry and the parent css */
- for_each_root_subsys(root, ss) {
- struct cgroup_subsys_state *css = css_ar[ss->subsys_id];
-
- dget(dentry);
- css_get(css->parent);
- }
-
/* hold a ref to the parent's dentry */
dget(parent->dentry);
@@ -4445,6 +4437,13 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
if (err)
goto err_destroy;
+ /* each css holds a ref to the cgroup's dentry and parent css */
+ dget(dentry);
+ css_get(css->parent);
+
+ /* mark it consumed for error path */
+ css_ar[ss->subsys_id] = NULL;
+
if (ss->broken_hierarchy && !ss->warned_broken_hierarchy &&
parent->parent) {
pr_warning("cgroup: %s (%d) created nested cgroup for controller \"%s\" which has incomplete hierarchy support. Nested cgroups may change behavior in the future.\n",
@@ -4491,6 +4490,14 @@ err_free_cgrp:
return err;
err_destroy:
+ for_each_root_subsys(root, ss) {
+ struct cgroup_subsys_state *css = css_ar[ss->subsys_id];
+
+ if (css) {
+ percpu_ref_cancel_init(&css->refcnt);
+ ss->css_free(css);
+ }
+ }
cgroup_destroy_locked(cgrp);
mutex_unlock(&cgroup_mutex);
mutex_unlock(&dentry->d_inode->i_mutex);
@@ -4652,8 +4659,12 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
* will be invoked to perform the rest of destruction once the
* percpu refs of all css's are confirmed to be killed.
*/
- for_each_root_subsys(cgrp->root, ss)
- kill_css(cgroup_css(cgrp, ss));
+ for_each_root_subsys(cgrp->root, ss) {
+ struct cgroup_subsys_state *css = cgroup_css(cgrp, ss);
+
+ if (css)
+ kill_css(css);
+ }
/*
* Mark @cgrp dead. This prevents further task migration and child