[BUG] general protection fault in cpuset_cpus_allowed

[Farhad Alemi]

Hello,

As part of the kernel research at ASU's SEFCOM
lab, we hit the crash below. Crash reports can be found here:

  https://github.com/farhad-alemi/public_bug_reports/tree/main/166-general-protection-fault-in-cpuset-cpus-allowed/

  Oops: general protection fault, probably for non-canonical address
0xdffffc000000001d: 0000 [#1] SMP KASAN NOPTI
  KASAN: null-ptr-deref in range [0x00000000000000e8-0x00000000000000ef]
  RIP: 0010:bitmap_intersects include/linux/bitmap.h:440 [inline]
  RIP: 0010:cpumask_intersects include/linux/cpumask.h:822 [inline]
  RIP: 0010:guarantee_active_cpus kernel/cgroup/cpuset.c:481 [inline]
  RIP: 0010:__cpuset_cpus_allowed_locked kernel/cgroup/cpuset.c:4022 [inline]
  RIP: 0010:cpuset_cpus_allowed+0x14a/0x2f0 kernel/cgroup/cpuset.c:4071
  Call Trace:
   cpuset_cpus_allowed+0x14a/0x2f0 kernel/cgroup/cpuset.c:4071
   __sched_setaffinity+0x98/0x3c0 kernel/sched/syscalls.c:1149
   sched_setaffinity+0x341/0x4a0 kernel/sched/syscalls.c:1237
   __x64_sys_sched_setaffinity+0x106/0x170 kernel/sched/syscalls.c:1262

A second capture reaches the identical fault -- same address, same KASAN range,
same RIP -- through cpuset_fork <- cgroup_post_fork <- copy_process <-
kernel_clone <- clone3, with the crashing task being systemd at PID 1.

Our reproducer.c is available upon request.

Happy to test a patch if that would help.

Regards,