linux.git/kernel/sched/psi.c, branch v5.10.258

sched/psi: Fix use-after-free in ep_remove_wait_queue()

2023-02-22T11:55:56+00:00

commit c2dbe32d5db5c4ead121cf86dabd5ab691fb47fe upstream.

If a non-root cgroup gets removed when there is a thread that registered
trigger and is polling on a pressure file within the cgroup, the polling
waitqueue gets freed in the following path:

 do_rmdir
   cgroup_rmdir
     kernfs_drain_open_files
       cgroup_file_release
         cgroup_pressure_release
           psi_trigger_destroy

However, the polling thread still has a reference to the pressure file and
will access the freed waitqueue when the file is closed or upon exit:

 fput
   ep_eventpoll_release
     ep_free
       ep_remove_wait_queue
         remove_wait_queue

This results in use-after-free as pasted below.

The fundamental problem here is that cgroup_file_release() (and
consequently waitqueue's lifetime) is not tied to the file's real lifetime.
Using wake_up_pollfree() here might be less than ideal, but it is in line
with the comment at commit 42288cb44c4b ("wait: add wake_up_pollfree()")
since the waitqueue's lifetime is not tied to file's one and can be
considered as another special case. While this would be fixable by somehow
making cgroup_file_release() be tied to the fput(), it would require
sizable refactoring at cgroups or higher layer which might be more
justifiable if we identify more cases like this.

  BUG: KASAN: use-after-free in _raw_spin_lock_irqsave+0x60/0xc0
  Write of size 4 at addr ffff88810e625328 by task a.out/4404

	CPU: 19 PID: 4404 Comm: a.out Not tainted 6.2.0-rc6 #38
	Hardware name: Amazon EC2 c5a.8xlarge/, BIOS 1.0 10/16/2017
	Call Trace:
	
	dump_stack_lvl+0x73/0xa0
	print_report+0x16c/0x4e0
	kasan_report+0xc3/0xf0
	kasan_check_range+0x2d2/0x310
	_raw_spin_lock_irqsave+0x60/0xc0
	remove_wait_queue+0x1a/0xa0
	ep_free+0x12c/0x170
	ep_eventpoll_release+0x26/0x30
	__fput+0x202/0x400
	task_work_run+0x11d/0x170
	do_exit+0x495/0x1130
	do_group_exit+0x100/0x100
	get_signal+0xd67/0xde0
	arch_do_signal_or_restart+0x2a/0x2b0
	exit_to_user_mode_prepare+0x94/0x100
	syscall_exit_to_user_mode+0x20/0x40
	do_syscall_64+0x52/0x90
	entry_SYSCALL_64_after_hwframe+0x63/0xcd
	

 Allocated by task 4404:

	kasan_set_track+0x3d/0x60
	__kasan_kmalloc+0x85/0x90
	psi_trigger_create+0x113/0x3e0
	pressure_write+0x146/0x2e0
	cgroup_file_write+0x11c/0x250
	kernfs_fop_write_iter+0x186/0x220
	vfs_write+0x3d8/0x5c0
	ksys_write+0x90/0x110
	do_syscall_64+0x43/0x90
	entry_SYSCALL_64_after_hwframe+0x63/0xcd

 Freed by task 4407:

	kasan_set_track+0x3d/0x60
	kasan_save_free_info+0x27/0x40
	____kasan_slab_free+0x11d/0x170
	slab_free_freelist_hook+0x87/0x150
	__kmem_cache_free+0xcb/0x180
	psi_trigger_destroy+0x2e8/0x310
	cgroup_file_release+0x4f/0xb0
	kernfs_drain_open_files+0x165/0x1f0
	kernfs_drain+0x162/0x1a0
	__kernfs_remove+0x1fb/0x310
	kernfs_remove_by_name_ns+0x95/0xe0
	cgroup_addrm_files+0x67f/0x700
	cgroup_destroy_locked+0x283/0x3c0
	cgroup_rmdir+0x29/0x100
	kernfs_iop_rmdir+0xd1/0x140
	vfs_rmdir+0xfe/0x240
	do_rmdir+0x13d/0x280
	__x64_sys_rmdir+0x2c/0x30
	do_syscall_64+0x43/0x90
	entry_SYSCALL_64_after_hwframe+0x63/0xcd

Fixes: 0e94682b73bf ("psi: introduce psi monitor")
Signed-off-by: Munehisa Kamata 
Signed-off-by: Mengchi Cheng 
Signed-off-by: Ingo Molnar 
Acked-by: Suren Baghdasaryan 
Acked-by: Peter Zijlstra 
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/lkml/20230106224859.4123476-1-kamatam@amazon.com/
Link: https://lore.kernel.org/r/20230214212705.4058045-1-kamatam@amazon.com
Signed-off-by: Greg Kroah-Hartman

psi: Fix uaf issue when psi trigger is destroyed while being polled

2022-02-05T11:37:55+00:00

commit a06247c6804f1a7c86a2e5398a4c1f1db1471848 upstream.

With write operation on psi files replacing old trigger with a new one,
the lifetime of its waitqueue is totally arbitrary. Overwriting an
existing trigger causes its waitqueue to be freed and pending poll()
will stumble on trigger->event_wait which was destroyed.
Fix this by disallowing to redefine an existing psi trigger. If a write
operation is used on a file descriptor with an already existing psi
trigger, the operation will fail with EBUSY error.
Also bypass a check for psi_disabled in the psi_trigger_destroy as the
flag can be flipped after the trigger is created, leading to a memory
leak.

Fixes: 0e94682b73bf ("psi: introduce psi monitor")
Reported-by: syzbot+cdb5dd11c97cc532efad@syzkaller.appspotmail.com
Suggested-by: Linus Torvalds 
Analyzed-by: Eric Biggers 
Signed-off-by: Suren Baghdasaryan 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Eric Biggers 
Acked-by: Johannes Weiner 
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20220111232309.1786347-1-surenb@google.com
[surenb: backported to 5.10 kernel]
CC: stable@vger.kernel.org # 5.10
Signed-off-by: Suren Baghdasaryan 
Signed-off-by: Greg Kroah-Hartman

psi: Fix race between psi_trigger_create/destroy

2021-07-14T14:56:10+00:00

[ Upstream commit 8f91efd870ea5d8bc10b0fcc9740db51cd4c0c83 ]

Race detected between psi_trigger_destroy/create as shown below, which
cause panic by accessing invalid psi_system->poll_wait->wait_queue_entry
and psi_system->poll_timer->entry->next. Under this modification, the
race window is removed by initialising poll_wait and poll_timer in
group_init which are executed only once at beginning.

  psi_trigger_destroy()                   psi_trigger_create()

  mutex_lock(trigger_lock);
  rcu_assign_pointer(poll_task, NULL);
  mutex_unlock(trigger_lock);
					  mutex_lock(trigger_lock);
					  if (!rcu_access_pointer(group->poll_task)) {
					    timer_setup(poll_timer, poll_timer_fn, 0);
					    rcu_assign_pointer(poll_task, task);
					  }
					  mutex_unlock(trigger_lock);

  synchronize_rcu();
  del_timer_sync(poll_timer); <-- poll_timer has been reinitialized by
                                  psi_trigger_create()

So, trigger_lock/RCU correctly protects destruction of
group->poll_task but misses this race affecting poll_timer and
poll_wait.

Fixes: 461daba06bdc ("psi: eliminate kthread_worker from psi trigger scheduling mechanism")
Co-developed-by: ziwei.dai 
Signed-off-by: ziwei.dai 
Co-developed-by: ke.wang 
Signed-off-by: ke.wang 
Signed-off-by: Zhaoyang Huang 
Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Suren Baghdasaryan 
Acked-by: Johannes Weiner 
Link: https://lkml.kernel.org/r/1623371374-15664-1-git-send-email-huangzhaoyang@gmail.com
Signed-off-by: Sasha Levin

sched,psi: Handle potential task count underflow bugs more gracefully

2021-05-11T12:47:31+00:00

[ Upstream commit 9d10a13d1e4c349b76f1c675a874a7f981d6d3b4 ]

psi_group_cpu->tasks, represented by the unsigned int, stores the
number of tasks that could be stalled on a psi resource(io/mem/cpu).
Decrementing these counters at zero leads to wrapping which further
leads to the psi_group_cpu->state_mask is being set with the
respective pressure state. This could result into the unnecessary time
sampling for the pressure state thus cause the spurious psi events.
This can further lead to wrong actions being taken at the user land
based on these psi events.

Though psi_bug is set under these conditions but that just for debug
purpose. Fix it by decrementing the ->tasks count only when it is
non-zero.

Signed-off-by: Charan Teja Reddy 
Signed-off-by: Peter Zijlstra (Intel) 
Acked-by: Johannes Weiner 
Link: https://lkml.kernel.org/r/1618585336-37219-1-git-send-email-charante@codeaurora.org
Signed-off-by: Sasha Levin

sched,psi: Convert to sched_set_fifo_low()

2020-06-15T12:10:25+00:00

Because SCHED_FIFO is a broken scheduler model (see previous patches)
take away the priority field, the kernel can't possibly make an
informed decision.

Effectively no change.

Signed-off-by: Peter Zijlstra (Intel) 
Reviewed-by: Ingo Molnar 
Acked-by: Johannes Weiner

psi: eliminate kthread_worker from psi trigger scheduling mechanism

2020-06-15T12:10:03+00:00

Each psi group requires a dedicated kthread_delayed_work and
kthread_worker. Since no other work can be performed using psi_group's
kthread_worker, the same result can be obtained using a task_struct and
a timer directly. This makes psi triggering simpler by removing lists
and locks involved with kthread_worker usage and eliminates the need for
poll_scheduled atomic use in the hot path.

Signed-off-by: Suren Baghdasaryan 
Signed-off-by: Peter Zijlstra (Intel) 
Link: https://lkml.kernel.org/r/20200528195442.190116-1-surenb@google.com

psi: Move PF_MEMSTALL out of task->flags

2020-03-20T12:06:19+00:00

The task->flags is a 32-bits flag, in which 31 bits have already been
consumed. So it is hardly to introduce other new per process flag.
Currently there're still enough spaces in the bit-field section of
task_struct, so we can define the memstall state as a single bit in
task_struct instead.
This patch also removes an out-of-date comment pointed by Matthew.

Suggested-by: Johannes Weiner 
Signed-off-by: Yafang Shao 
Signed-off-by: Peter Zijlstra (Intel) 
Acked-by: Johannes Weiner 
Link: https://lkml.kernel.org/r/1584408485-1921-1-git-send-email-laoar.shao@gmail.com

psi: Optimize switching tasks inside shared cgroups

2020-03-20T12:06:19+00:00

When switching tasks running on a CPU, the psi state of a cgroup
containing both of these tasks does not change. Right now, we don't
exploit that, and can perform many unnecessary state changes in nested
hierarchies, especially when most activity comes from one leaf cgroup.

This patch implements an optimization where we only update cgroups
whose state actually changes during a task switch. These are all
cgroups that contain one task but not the other, up to the first
shared ancestor. When both tasks are in the same group, we don't need
to update anything at all.

We can identify the first shared ancestor by walking the groups of the
incoming task until we see TSK_ONCPU set on the local CPU; that's the
first group that also contains the outgoing task.

The new psi_task_switch() is similar to psi_task_change(). To allow
code reuse, move the task flag maintenance code into a new function
and the poll/avg worker wakeups into the shared psi_group_change().

Suggested-by: Peter Zijlstra 
Signed-off-by: Johannes Weiner 
Signed-off-by: Peter Zijlstra (Intel) 
Link: https://lkml.kernel.org/r/20200316191333.115523-3-hannes@cmpxchg.org

psi: Fix cpu.pressure for cpu.max and competing cgroups

2020-03-20T12:06:18+00:00

For simplicity, cpu pressure is defined as having more than one
runnable task on a given CPU. This works on the system-level, but it
has limitations in a cgrouped reality: When cpu.max is in use, it
doesn't capture the time in which a task is not executing on the CPU
due to throttling. Likewise, it doesn't capture the time in which a
competing cgroup is occupying the CPU - meaning it only reflects
cgroup-internal competitive pressure, not outside pressure.

Enable tracking of currently executing tasks, and then change the
definition of cpu pressure in a cgroup from

	NR_RUNNING > 1

to

	NR_RUNNING > ON_CPU

which will capture the effects of cpu.max as well as competition from
outside the cgroup.

After this patch, a cgroup running `stress -c 1` with a cpu.max
setting of 5000 10000 shows ~50% continuous CPU pressure.

Signed-off-by: Johannes Weiner 
Signed-off-by: Peter Zijlstra (Intel) 
Link: https://lkml.kernel.org/r/20200316191333.115523-2-hannes@cmpxchg.org

Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

2020-02-15T20:51:22+00:00

Pull scheduler fixes from Ingo Molnar:
 "Misc fixes all over the place:

   - Fix NUMA over-balancing between lightly loaded nodes. This is
     fallout of the big load-balancer rewrite.

   - Fix the NOHZ remote loadavg update logic, which fixes anomalies
     like reported 150 loadavg on mostly idle CPUs.

   - Fix XFS performance/scalability

   - Fix throttled groups unbound task-execution bug

   - Fix PSI procfs boundary condition

   - Fix the cpu.uclamp.{min,max} cgroup configuration write checks

   - Fix DocBook annotations

   - Fix RCU annotations

   - Fix overly CPU-intensive housekeeper CPU logic loop on large CPU
     counts"

* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  sched/fair: Fix kernel-doc warning in attach_entity_load_avg()
  sched/core: Annotate curr pointer in rq with __rcu
  sched/psi: Fix OOB write when writing 0 bytes to PSI files
  sched/fair: Allow a per-CPU kthread waking a task to stack on the same CPU, to fix XFS performance regression
  sched/fair: Prevent unlimited runtime on throttled group
  sched/nohz: Optimize get_nohz_timer_target()
  sched/uclamp: Reject negative values in cpu_uclamp_write()
  sched/fair: Allow a small load imbalance between low utilisation SD_NUMA domains
  timers/nohz: Update NOHZ load in remote tick
  sched/core: Don't skip remote tick for idle CPUs