linux-stable.git/kernel/cgroup, branch v6.18.40

cgroup/cpuset: rebind mm mempolicy to effective_mems, not mems_allowed

2026-07-24T14:17:17+00:00

commit b983c56426383e4a06fa5970c4e33cee879b1482 upstream.

Creating a child cpuset where cpuset.mems is never set leads to a div/0
when a VMA mempolicy with MPOL_F_RELATIVE_NODES rebinds in response to a
CPU hotplug event.

Reproduction steps:
 1) Create a cgroup w/ cpuset controls (do not set cpuset.mems)
 2) Move the task into the child cpuset
 3) Create a VMA mempolicy for that task with MPOL_F_RELATIVE_NODES
 4) unplug and hotplug a cpu
      echo 0 > /sys/devices/system/cpu/cpu1/online
      echo 1 > /sys/devices/system/cpu/cpu1/online
 5) mempolicy rebind does a div/0 in mpol_relative_nodemask on the
    call to __nodes_fold()

The cpuset code passes (cs->mems_allowed) which is not guaranteed to have
nodes to the rebind routine.  Use cs->effective_mems instead, which is
guaranteed to have a non-empty nodemask once we reach that code path.

Link: https://lore.kernel.org/all/CA+0ovCiEz6SP_sn3kN4Tb+_oC=eHMXy_Ffj=usV3wREdQrUtww@mail.gmail.com/
Fixes: ae1c802382f7 ("cpuset: apply cs->effective_{cpus,mems}")
Closes: https://lore.kernel.org/linux-mm/CA+0ovCgxbZkXa+OU8w3s84R3KNPNxxRfmsNR-udh+afQBbGNmw@mail.gmail.com/
Suggested-by: Gregory Price 
Suggested-by: Waiman Long 
Acked-by: Waiman Long 
Signed-off-by: Farhad Alemi 
Cc: Andrew Morton 
Cc: Alistair Popple 
Cc: Byungchul Park 
Cc: Gregory Price 
Cc: "Huang, Ying" 
Cc: Joshua Hahn 
Cc: Matthew Brost 
Cc: Rakie Kim 
Cc: Rasmus Villemoes 
Cc: Zi Yan 
Cc: Tejun Heo 
Cc: Ridong Chen 
Cc: Johannes Weiner 
Cc: "Michal Koutný" 
Cc: 
[ david: add a comment, slightly rephrase description ]
Signed-off-by: David Hildenbrand (Arm) 
Signed-off-by: Tejun Heo 
Signed-off-by: Greg Kroah-Hartman

cgroup: rstat: relax NMI guard after switch to try_cmpxchg

2026-06-01T15:51:05+00:00

[ Upstream commit 22572dbcd3486e6c4dced877125bbf50e4e24edf ]

Commit 36df6e3dbd7e ("cgroup: make css_rstat_updated nmi safe") used
this_cpu_cmpxchg() for the lockless insertion, and therefore required
both ARCH_HAVE_NMI_SAFE_CMPXCHG and ARCH_HAS_NMI_SAFE_THIS_CPU_OPS in
the NMI guard: on archs without the latter, this_cpu_cmpxchg() falls
back to "local_irq_save() + plain cmpxchg", and local_irq_save()
cannot mask NMIs.

Commit 3309b63a2281 ("cgroup: rstat: use LOCK CMPXCHG in
css_rstat_updated") later replaced this_cpu_cmpxchg() with plain
try_cmpxchg() to fix cross-CPU lockless-list corruption, but left the
NMI guard untouched.  After that switch, css_rstat_updated() no longer
performs any this_cpu_*() RMW operations and only relies on the arch
having NMI-safe cmpxchg, so ARCH_HAS_NMI_SAFE_THIS_CPU_OPS is no
longer required in the guard.

Relax the guard accordingly so that archs which have HAVE_NMI and
ARCH_HAVE_NMI_SAFE_CMPXCHG but not ARCH_HAS_NMI_SAFE_THIS_CPU_OPS
(e.g. sparc, powerpc on PPC64/BOOK3S) can benefit from the existing
CONFIG_MEMCG_NMI_SAFETY_REQUIRES_ATOMIC path.  Without this, the css
is never queued in NMI on those archs, and the atomics staged by
account_{slab,kmem}_nmi_safe() are not drained by flush_nmi_stats().

Fixes: 3309b63a2281 ("cgroup: rstat: use LOCK CMPXCHG in css_rstat_updated")
Signed-off-by: Cunlong Li 
Signed-off-by: Tejun Heo 
Signed-off-by: Sasha Levin

cgroup/rstat: validate cpu before css_rstat_cpu() access

2026-06-01T15:51:03+00:00

[ Upstream commit 8817005efbdfdf5d4e4814cb5dc52b53d12917d7 ]

css_rstat_updated() is exposed as a BPF kfunc and accepts a
caller-provided cpu argument. The function uses cpu for per-cpu rstat
lookups without checking whether it refers to a valid possible CPU.

A BPF iter/cgroup program with CAP_BPF and CAP_PERFMON can pass an
invalid cpu value. On an unfixed UBSCAN_BOUNDS test kernel, cpu ==
0x7fffffff triggers:

  UBSAN: array-index-out-of-bounds in kernel/cgroup/rstat.c:31:9
  index 2147483647 is out of range for type 'long unsigned int [64]'
  Call Trace:
    css_rstat_updated
    bpf_iter_run_prog
    cgroup_iter_seq_show
    bpf_seq_read

Add cpu validation to the BPF-facing css_rstat_updated() kfunc and
move the common implementation to __css_rstat_updated() for in-kernel
callers.

Fixes: a319185be9f5 ("cgroup: bpf: enable bpf programs to integrate with rstat")
Signed-off-by: Qing Ming 
Signed-off-by: Tejun Heo 
Signed-off-by: Sasha Levin

cgroup/cpuset: Reset DL migration state on can_attach() failure

2026-06-01T15:50:43+00:00

[ Upstream commit 4a39eda5fdd867fc39f3c039714dd432cee00268 ]

cpuset_can_attach() accumulates temporary SCHED_DEADLINE migration
state in the destination cpuset while walking the taskset.

If a later task_can_attach() or security_task_setscheduler() check
fails, cgroup_migrate_execute() treats cpuset as the failing subsystem
and does not call cpuset_cancel_attach() for it. The partially
accumulated state is then left behind and can be consumed by a later
attach, corrupting cpuset DL task accounting and pending DL bandwidth
accounting.

Reset the pending DL migration state from the common error exit when
ret is non-zero. Successful can_attach() keeps the state for
cpuset_attach() or cpuset_cancel_attach().

Fixes: 2ef269ef1ac0 ("cgroup/cpuset: Free DL BW in case can_attach() fails")
Cc: stable@vger.kernel.org # v6.10+
Signed-off-by: Guopeng Zhang 
Signed-off-by: Tejun Heo 
Reviewed-by: Chen Ridong 
Reviewed-by: Waiman Long 
[ omitted upstream context line `cs->dl_bw_cpu = cpu;` ]
Signed-off-by: Sasha Levin 
Signed-off-by: Greg Kroah-Hartman

cgroup/dmem: Return -ENOMEM on failed pool preallocation

2026-05-23T11:07:16+00:00

commit 796ad622040f7f955ccc3973085e953415920496 upstream.

get_cg_pool_unlocked() handles allocation failures under dmemcg_lock by
dropping the lock, preallocating a pool with GFP_KERNEL, and retrying the
locked lookup and creation path.

If the fallback allocation fails too, pool remains NULL. Since the loop
condition is while (!pool), the function can keep retrying instead of
propagating the allocation failure to the caller.

Set pool to ERR_PTR(-ENOMEM) when the fallback allocation fails so the
loop exits through the existing common return path. The callers already
handle ERR_PTR() from get_cg_pool_unlocked(), so this restores the
expected error path.

Fixes: b168ed458dde ("kernel/cgroup: Add "dmem" memory accounting cgroup")
Cc: stable@vger.kernel.org # v6.14+
Signed-off-by: Guopeng Zhang 
Signed-off-by: Tejun Heo 
Signed-off-by: Greg Kroah-Hartman

cgroup: Increment nr_dying_subsys_* from rmdir context

2026-05-23T11:07:07+00:00

[ Upstream commit 13e786b64bd3fd81c7eb22aa32bf8305c32f2ccf ]

Incrementing nr_dying_subsys_* in offline_css(), which is executed by
cgroup_offline_wq worker, leads to a race where user can see the value
to be 0 if he reads cgroup.stat after calling rmdir and before the worker
executes. This makes the user wrongly expect resources released by the
removed cgroup to be available for a new assignment.

Increment nr_dying_subsys_* from kill_css(), which is called from the
cgroup_rmdir() context.

Fixes: ab0312526867 ("cgroup: Show # of subsystem CSSes in cgroup.stat")
Signed-off-by: Petr Malat 
Signed-off-by: Tejun Heo 
Signed-off-by: Sasha Levin

cgroup/rdma: fix integer overflow in rdmacg_try_charge()

2026-05-23T11:07:06+00:00

[ Upstream commit c802f460dd485c1332b5a35e7adcfb2bc22536a2 ]

The expression `rpool->resources[index].usage + 1` is computed in int
arithmetic before being assigned to s64 variable `new`. When usage equals
INT_MAX (the default "max" value), the addition overflows to INT_MIN.
This negative value then passes the `new > max` check incorrectly,
allowing a charge that should be rejected and corrupting usage to
negative.

Fix by casting usage to s64 before the addition so the arithmetic is
done in 64-bit.

Fixes: 39d3e7584a68 ("rdmacg: Added rdma cgroup controller")
Signed-off-by: cuitao 
Reviewed-by: Michal Koutný 
Signed-off-by: Tejun Heo 
Signed-off-by: Sasha Levin

sched/psi: fix race between file release and pressure write

2026-05-23T11:07:06+00:00

[ Upstream commit a5b98009f16d8a5fb4a8ff9a193f5735515c38fa ]

A potential race condition exists between pressure write and cgroup file
release regarding the priv member of struct kernfs_open_file, which
triggers the uaf reported in [1].

Consider the following scenario involving execution on two separate CPUs:

   CPU0					CPU1
   ====					====
					vfs_rmdir()
					kernfs_iop_rmdir()
					cgroup_rmdir()
					cgroup_kn_lock_live()
					cgroup_destroy_locked()
					cgroup_addrm_files()
					cgroup_rm_file()
					kernfs_remove_by_name()
					kernfs_remove_by_name_ns()
 vfs_write()				__kernfs_remove()
 new_sync_write()			kernfs_drain()
 kernfs_fop_write_iter()		kernfs_drain_open_files()
 cgroup_file_write()			kernfs_release_file()
 pressure_write()			cgroup_file_release()
 ctx = of->priv;
					kfree(ctx);
 					of->priv = NULL;
					cgroup_kn_unlock()
 cgroup_kn_lock_live()
 cgroup_get(cgrp)
 cgroup_kn_unlock()
 if (ctx->psi.trigger)  // here, trigger uaf for ctx, that is of->priv

The cgroup_rmdir() is protected by the cgroup_mutex, it also safeguards
the memory deallocation of of->priv performed within cgroup_file_release().
However, the operations involving of->priv executed within pressure_write()
are not entirely covered by the protection of cgroup_mutex. Consequently,
if the code in pressure_write(), specifically the section handling the
ctx variable executes after cgroup_file_release() has completed, a uaf
vulnerability involving of->priv is triggered.

Therefore, the issue can be resolved by extending the scope of the
cgroup_mutex lock within pressure_write() to encompass all code paths
involving of->priv, thereby properly synchronizing the race condition
occurring between cgroup_file_release() and pressure_write().

And, if an live kn lock can be successfully acquired while executing
the pressure write operation, it indicates that the cgroup deletion
process has not yet reached its final stage; consequently, the priv
pointer within open_file cannot be NULL. Therefore, the operation to
retrieve the ctx value must be moved to a point *after* the live kn
lock has been successfully acquired.

In another situation, specifically after entering cgroup_kn_lock_live()
but before acquiring cgroup_mutex, there exists a different class of
race condition:

CPU0: write memory.pressure               CPU1: write cgroup.pressure=0
===========================		  =============================

kernfs_fop_write_iter()
 kernfs_get_active_of(of)
 pressure_write()
   cgroup_kn_lock_live(memory.pressure)
     cgroup_tryget(cgrp)
     kernfs_break_active_protection(kn)
     ... blocks on cgroup_mutex

                                     	  cgroup_pressure_write()
                                     	  cgroup_kn_lock_live(cgroup.pressure)
                                     	  cgroup_file_show(memory.pressure, false)
                                     	    kernfs_show(false)
                                     	      kernfs_drain_open_files()
                                     	        cgroup_file_release(of)
                                     	          kfree(ctx)
                                     	            of->priv = NULL
                                     	  cgroup_kn_unlock()

   ... acquires cgroup_mutex
   ctx = of->priv;        // may now be NULL
   if (ctx->psi.trigger)  // NULL dereference

Consequently, there is a possibility that of->priv is NULL, the pressure
write needs to check for this.

Now that the scope of the cgroup_mutex has been expanded, the original
explicit cgroup_get/put operations are no longer necessary, this is
because acquiring/releasing the live kn lock inherently executes a
cgroup get/put operation.

[1]
BUG: KASAN: slab-use-after-free in pressure_write+0xa4/0x210 kernel/cgroup/cgroup.c:4011
Call Trace:
 pressure_write+0xa4/0x210 kernel/cgroup/cgroup.c:4011
 cgroup_file_write+0x36f/0x790 kernel/cgroup/cgroup.c:4311
 kernfs_fop_write_iter+0x3b0/0x540 fs/kernfs/file.c:352

Allocated by task 9352:
 cgroup_file_open+0x90/0x3a0 kernel/cgroup/cgroup.c:4256
 kernfs_fop_open+0x9eb/0xcb0 fs/kernfs/file.c:724
 do_dentry_open+0x83d/0x13e0 fs/open.c:949

Freed by task 9353:
 cgroup_file_release+0xd6/0x100 kernel/cgroup/cgroup.c:4283
 kernfs_release_file fs/kernfs/file.c:764 [inline]
 kernfs_drain_open_files+0x392/0x720 fs/kernfs/file.c:834
 kernfs_drain+0x470/0x600 fs/kernfs/dir.c:525

Fixes: 0e94682b73bf ("psi: introduce psi monitor")
Reported-by: syzbot+33e571025d88efd1312c@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=33e571025d88efd1312c
Tested-by: syzbot+33e571025d88efd1312c@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis 
Reviewed-by: Chen Ridong 
Signed-off-by: Tejun Heo 
Signed-off-by: Sasha Levin

cgroup: fix race between task migration and iteration

2026-03-19T15:08:22+00:00

commit 5ee01f1a7343d6a3547b6802ca2d4cdce0edacb1 upstream.

When a task is migrated out of a css_set, cgroup_migrate_add_task()
first moves it from cset->tasks to cset->mg_tasks via:

    list_move_tail(&task->cg_list, &cset->mg_tasks);

If a css_task_iter currently has it->task_pos pointing to this task,
css_set_move_task() calls css_task_iter_skip() to keep the iterator
valid. However, since the task has already been moved to ->mg_tasks,
the iterator is advanced relative to the mg_tasks list instead of the
original tasks list. As a result, remaining tasks on cset->tasks, as
well as tasks queued on cset->mg_tasks, can be skipped by iteration.

Fix this by calling css_set_skip_task_iters() before unlinking
task->cg_list from cset->tasks. This advances all active iterators to
the next task on cset->tasks, so iteration continues correctly even
when a task is concurrently being migrated.

This race is hard to hit in practice without instrumentation, but it
can be reproduced by artificially slowing down cgroup_procs_show().
For example, on an Android device a temporary
/sys/kernel/cgroup/cgroup_test knob can be added to inject a delay
into cgroup_procs_show(), and then:

  1) Spawn three long-running tasks (PIDs 101, 102, 103).
  2) Create a test cgroup and move the tasks into it.
  3) Enable a large delay via /sys/kernel/cgroup/cgroup_test.
  4) In one shell, read cgroup.procs from the test cgroup.
  5) Within the delay window, in another shell migrate PID 102 by
     writing it to a different cgroup.procs file.

Under this setup, cgroup.procs can intermittently show only PID 101
while skipping PID 103. Once the migration completes, reading the
file again shows all tasks as expected.

Note that this change does not allow removing the existing
css_set_skip_task_iters() call in css_set_move_task(). The new call
in cgroup_migrate_add_task() only handles iterators that are racing
with migration while the task is still on cset->tasks. Iterators may
also start after the task has been moved to cset->mg_tasks. If we
dropped css_set_skip_task_iters() from css_set_move_task(), such
iterators could keep task_pos pointing to a migrating task, causing
css_task_iter_advance() to malfunction on the destination css_set,
up to and including crashes or infinite loops.

The race window between migration and iteration is very small, and
css_task_iter is not on a hot path. In the worst case, when an
iterator is positioned on the first thread of the migrating process,
cgroup_migrate_add_task() may have to skip multiple tasks via
css_set_skip_task_iters(). However, this only happens when migration
and iteration actually race, so the performance impact is negligible
compared to the correctness fix provided here.

Fixes: b636fd38dc40 ("cgroup: Implement css_task_iter_skip()")
Cc: stable@vger.kernel.org # v5.2+
Signed-off-by: Qingye Zhao 
Reviewed-by: Michal Koutný 
Signed-off-by: Tejun Heo 
Signed-off-by: Greg Kroah-Hartman

cgroup/cpuset: Fix incorrect use of cpuset_update_tasks_cpumask() in update_cpumasks_hier()

2026-03-12T11:09:14+00:00

[ Upstream commit 68230aac8b9aad243626fbaf3ca170012c17fec5 ]

Commit e2ffe502ba45 ("cgroup/cpuset: Add cpuset.cpus.exclusive for v2")
incorrectly changed the 2nd parameter of cpuset_update_tasks_cpumask()
from tmp->new_cpus to cp->effective_cpus. This second parameter is just
a temporary cpumask for internal use. The cpuset_update_tasks_cpumask()
function was originally called update_tasks_cpumask() before commit
381b53c3b549 ("cgroup/cpuset: rename functions shared between v1
and v2").

This mistake can incorrectly change the effective_cpus of the
cpuset when it is the top_cpuset or in arm64 architecture where
task_cpu_possible_mask() may differ from cpu_possible_mask.  So far
top_cpuset hasn't been passed to update_cpumasks_hier() yet, but arm64
arch can still be impacted. Fix it by reverting the incorrect change.

Fixes: e2ffe502ba45 ("cgroup/cpuset: Add cpuset.cpus.exclusive for v2")
Signed-off-by: Waiman Long 
Signed-off-by: Tejun Heo 
Signed-off-by: Sasha Levin