BUG: unable to handle kernel NULL pointer dereference in guarantee_active_cpus

Status: moderation: reported on 2026/10/05 07:41
Subsystems: cgroups
Labels: prio:high
[Documentation on labels]
Reported-by: syzbot+0bf8681dc0369b02edd1@syzkaller.appspotmail.com
First crash: 4d05h, last: 4d05h
▶ ▼ ✨ AI Jobs (2)
ID Workflow Result Correct Bug Created Started Finished Revision
02b12f11 repro-c 💥 BUG: unable to handle kernel NULL pointer dereference in guarantee_active_cpus 2026/10/04 04:26 2026/10/04 04:26 2026/10/04 04:53 57bbd979
cd7d7429 assessment-security DenialOfService: ✅ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ✅ UserNamespace: ✅ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ BUG: unable to handle kernel NULL pointer dereference in guarantee_active_cpus 2026/10/03 00:05 2026/10/03 00:05 2026/10/03 00:40 57bbd979

Sample crash report:
Unable to handle kernel NULL pointer dereference at virtual address 0000000000000110
Mem abort info:
  ESR = 0x0000000096000006
  EC = 0x25: DABT (current EL), IL = 32 bits
  SET = 0, FnV = 0
  EA = 0, S1PTW = 0
  FSC = 0x06: level 2 translation fault
Data abort info:
  ISV = 0, ISS = 0x00000006, ISS2 = 0x00000000
  CM = 0, WnR = 0, TnD = 0, TagAccess = 0
  GCS = 0, Overlay = 0, DirtyBit = 0
user pgtable: 4k pages, 52-bit VAs, pgdp=000000004b47d680
[0000000000000110] pgd=080000004ef47403, p4d=080000007e679403, pud=080000004c940403, pmd=0000000000000000
Internal error: Oops: 0000000096000006 [#1]  SMP
Modules linked in:
CPU: 0 UID: 0 PID: 9725 Comm: syz.2.1882 Not tainted syzkaller #0 PREEMPT 
Hardware name: linux,dummy-virt (DT)
pstate: 414020c9 (nZcv daIF +PAN -UAO -TCO +DIT -SSBS BTYPE=--)
pc : bitmap_intersects include/linux/bitmap.h:443 [inline]
pc : cpumask_intersects include/linux/cpumask.h:823 [inline]
pc : guarantee_active_cpus+0x64/0xc4 kernel/cgroup/cpuset.c:516
lr : rcu_read_lock include/linux/rcupdate.h:847 [inline]
lr : guarantee_active_cpus+0x44/0xc4 kernel/cgroup/cpuset.c:513
sp : ffff800083033cd0
x29: ffff800083033cd0 x28: f6f000000356a200 x27: 0000000000000000
x26: 0000000000000000 x25: 0000000000000000 x24: 0000000000000000
x23: fffffffffffffff4 x22: 0000000000000000 x21: f6f000000cd11100
x20: f6f000000cd11100 x19: ffff800083033d28 x18: 0000000000000000
x17: 0000000000000000 x16: 0000000000000000 x15: 0000000020000240
x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000
x11: 0000000000000040 x10: f1f0000004097b88 x9 : 0000000000000068
x8 : f5f000000662b53c x7 : 0000000000000003 x6 : 0000000000000003
x5 : 0000000000000007 x4 : 0000000000000008 x3 : 0000000000000001
x2 : 0000000000000000 x1 : f6f000000356a200 x0 : 0000000000000000
Call trace:
 parent_cs kernel/cgroup/cpuset-internal.h:209 [inline] (P)
 guarantee_active_cpus+0x64/0xc4 kernel/cgroup/cpuset.c:517 (P)
 __cpuset_cpus_allowed_locked kernel/cgroup/cpuset.c:4202 [inline]
 cpuset_cpus_allowed+0x54/0xc4 kernel/cgroup/cpuset.c:4251
 __sched_setaffinity+0x40/0x128 kernel/sched/syscalls.c:1149
 sched_setaffinity+0x120/0x23c kernel/sched/syscalls.c:1237
 __do_sys_sched_setaffinity kernel/sched/syscalls.c:1273 [inline]
 __se_sys_sched_setaffinity kernel/sched/syscalls.c:1262 [inline]
 __arm64_sys_sched_setaffinity+0x68/0xd4 kernel/sched/syscalls.c:1262
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall+0x54/0x10c arch/arm64/kernel/syscall.c:49
 el0_svc_common.constprop.0+0x40/0xe0 arch/arm64/kernel/syscall.c:121
 do_el0_svc+0x1c/0x34 arch/arm64/kernel/syscall.c:140
 el0_svc+0x38/0x1fc arch/arm64/kernel/entry-common.c:758
 el0t_64_sync_handler+0xa0/0xe4 arch/arm64/kernel/entry-common.c:777
 el0t_64_sync+0x1a4/0x1a8 arch/arm64/kernel/entry.S:590
Code: 8a000060 f2401c00 540000c1 f9405c42 (f9408840) 
---[ end trace 0000000000000000 ]---
----------------
Code disassembly (best guess):
   0:	8a000060 	and	x0, x3, x0
   4:	f2401c00 	ands	x0, x0, #0xff
   8:	540000c1 	b.ne	0x20  // b.any
   c:	f9405c42 	ldr	x2, [x2, #184]
* 10:	f9408840 	ldr	x0, [x2, #272] <-- trapping instruction

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/10/01 07:29 https://kernel.googlesource.com/pub/scm/linux/kernel/git/torvalds/linux master 551c722f4080 38f7f0d1 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu2-arm64-mte BUG: unable to handle kernel NULL pointer dereference in guarantee_active_cpus
* Struck through repros no longer work on HEAD.