This is a note to let you know that I've just added the patch titled
cgroup: Do not corrupt task iteration when rebinding subsystem
to the 5.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
cgroup-do-not-corrupt-task-iteration-when-rebinding-subsystem.patch
and it can be found in the queue-5.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 6f363f5aa845561f7ea496d8b1175e3204470486 Mon Sep 17 00:00:00 2001
From: Xiu Jianfeng <xiujianfeng@xxxxxxxxxx>
Date: Sat, 10 Jun 2023 17:26:43 +0800
Subject: cgroup: Do not corrupt task iteration when rebinding subsystem
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
From: Xiu Jianfeng <xiujianfeng@xxxxxxxxxx>
commit 6f363f5aa845561f7ea496d8b1175e3204470486 upstream.
We found a refcount UAF bug as follows:
refcount_t: addition on 0; use-after-free.
WARNING: CPU: 1 PID: 342 at lib/refcount.c:25 refcount_warn_saturate+0xa0/0x148
Workqueue: events cpuset_hotplug_workfn
Call trace:
refcount_warn_saturate+0xa0/0x148
__refcount_add.constprop.0+0x5c/0x80
css_task_iter_advance_css_set+0xd8/0x210
css_task_iter_advance+0xa8/0x120
css_task_iter_next+0x94/0x158
update_tasks_root_domain+0x58/0x98
rebuild_root_domains+0xa0/0x1b0
rebuild_sched_domains_locked+0x144/0x188
cpuset_hotplug_workfn+0x138/0x5a0
process_one_work+0x1e8/0x448
worker_thread+0x228/0x3e0
kthread+0xe0/0xf0
ret_from_fork+0x10/0x20
then a kernel panic will be triggered as below:
Unable to handle kernel paging request at virtual address 00000000c0000010
Call trace:
cgroup_apply_control_disable+0xa4/0x16c
rebind_subsystems+0x224/0x590
cgroup_destroy_root+0x64/0x2e0
css_free_rwork_fn+0x198/0x2a0
process_one_work+0x1d4/0x4bc
worker_thread+0x158/0x410
kthread+0x108/0x13c
ret_from_fork+0x10/0x18
The race that cause this bug can be shown as below:
(hotplug cpu) | (umount cpuset)
mutex_lock(&cpuset_mutex) | mutex_lock(&cgroup_mutex)
cpuset_hotplug_workfn |
rebuild_root_domains | rebind_subsystems
update_tasks_root_domain | spin_lock_irq(&css_set_lock)
css_task_iter_start | list_move_tail(&cset->e_cset_node[ss->id]
while(css_task_iter_next) | &dcgrp->e_csets[ss->id]);
css_task_iter_end | spin_unlock_irq(&css_set_lock)
mutex_unlock(&cpuset_mutex) | mutex_unlock(&cgroup_mutex)
Inside css_task_iter_start/next/end, css_set_lock is hold and then
released, so when iterating task(left side), the css_set may be moved to
another list(right side), then it->cset_head points to the old list head
and it->cset_pos->next points to the head node of new list, which can't
be used as struct css_set.
To fix this issue, switch from all css_sets to only scgrp's css_sets to
patch in-flight iterators to preserve correct iteration, and then
update it->cset_head as well.
Reported-by: Gaosheng Cui <cuigaosheng1@xxxxxxxxxx>
Link: https://www.spinics.net/lists/cgroups/msg37935.html
Suggested-by: Michal Koutný <mkoutny@xxxxxxxx>
Link: https://lore.kernel.org/all/20230526114139.70274-1-xiujianfeng@xxxxxxxxxxxxxxx/
Signed-off-by: Xiu Jianfeng <xiujianfeng@xxxxxxxxxx>
Fixes: 2d8f243a5e6e ("cgroup: implement cgroup->e_csets[]")
Cc: stable@xxxxxxxxxxxxxxx # v3.16+
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/cgroup/cgroup.c | 20 +++++++++++++++++---
1 file changed, 17 insertions(+), 3 deletions(-)
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -1723,7 +1723,7 @@ int rebind_subsystems(struct cgroup_root
{
struct cgroup *dcgrp = &dst_root->cgrp;
struct cgroup_subsys *ss;
- int ssid, i, ret;
+ int ssid, ret;
u16 dfl_disable_ss_mask = 0;
lockdep_assert_held(&cgroup_mutex);
@@ -1767,7 +1767,8 @@ int rebind_subsystems(struct cgroup_root
struct cgroup_root *src_root = ss->root;
struct cgroup *scgrp = &src_root->cgrp;
struct cgroup_subsys_state *css = cgroup_css(scgrp, ss);
- struct css_set *cset;
+ struct css_set *cset, *cset_pos;
+ struct css_task_iter *it;
WARN_ON(!css || cgroup_css(dcgrp, ss));
@@ -1785,9 +1786,22 @@ int rebind_subsystems(struct cgroup_root
css->cgroup = dcgrp;
spin_lock_irq(&css_set_lock);
- hash_for_each(css_set_table, i, cset, hlist)
+ WARN_ON(!list_empty(&dcgrp->e_csets[ss->id]));
+ list_for_each_entry_safe(cset, cset_pos, &scgrp->e_csets[ss->id],
+ e_cset_node[ss->id]) {
list_move_tail(&cset->e_cset_node[ss->id],
&dcgrp->e_csets[ss->id]);
+ /*
+ * all css_sets of scgrp together in same order to dcgrp,
+ * patch in-flight iterators to preserve correct iteration.
+ * since the iterator is always advanced right away and
+ * finished when it->cset_pos meets it->cset_head, so only
+ * update it->cset_head is enough here.
+ */
+ list_for_each_entry(it, &cset->task_iters, iters_node)
+ if (it->cset_head == &scgrp->e_csets[ss->id])
+ it->cset_head = &dcgrp->e_csets[ss->id];
+ }
spin_unlock_irq(&css_set_lock);
/* default hierarchy doesn't enable controllers by default */
Patches currently in stable-queue which might be from xiujianfeng@xxxxxxxxxx are
queue-5.4/cgroup-do-not-corrupt-task-iteration-when-rebinding-subsystem.patch
