CVE-2023-52707

In the Linux kernel, the following vulnerability has been resolved:

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

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:

<TASK>

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

</TASK>

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