cgroup/cpuset: fix panic caused by partcmd_update
CVE: CVE-2024-44975
Component: kernel
CWE: CWE-664
Severity: Moderate
CVSS v3: 5.1/AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
Release date: 2024-09-04T00:00:00+00:00

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

cgroup/cpuset: fix panic caused by partcmd_update

We find a bug as below:
BUG: unable to handle page fault for address: 00000003
PGD 0 P4D 0
Oops: 0000 [#1] PREEMPT SMP NOPTI
CPU: 3 PID: 358 Comm: bash Tainted: G        W I        6.6.0-10893-g60d6
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/4
RIP: 0010:partition_sched_domains_locked+0x483/0x600
Code: 01 48 85 d2 74 0d 48 83 05 29 3f f8 03 01 f3 48 0f bc c2 89 c0 48 9
RSP: 0018:ffffc90000fdbc58 EFLAGS: 00000202
RAX: 0000000100000003 RBX: ffff888100b3dfa0 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 000000000002fe80
RBP: ffff888100b3dfb0 R08: 0000000000000001 R09: 0000000000000000
R10: ffffc90000fdbcb0 R11: 0000000000000004 R12: 0000000000000002
R13: ffff888100a92b48 R14: 0000000000000000 R15: 0000000000000000
FS:  00007f44a5425740(0000) GS:ffff888237d80000(0000) knlGS:0000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000100030973 CR3: 000000010722c000 CR4: 00000000000006e0
Call Trace:
 <TASK>
 ? show_regs+0x8c/0xa0
 ? __die_body+0x23/0xa0
 ? __die+0x3a/0x50
 ? page_fault_oops+0x1d2/0x5c0
 ? partition_sched_domains_locked+0x483/0x600
 ? search_module_extables+0x2a/0xb0
 ? search_exception_tables+0x67/0x90
 ? kernelmode_fixup_or_oops+0x144/0x1b0
 ? __bad_area_nosemaphore+0x211/0x360
 ? up_read+0x3b/0x50
 ? bad_area_nosemaphore+0x1a/0x30
 ? exc_page_fault+0x890/0xd90
 ? __lock_acquire.constprop.0+0x24f/0x8d0
 ? __lock_acquire.constprop.0+0x24f/0x8d0
 ? asm_exc_page_fault+0x26/0x30
 ? partition_sched_domains_locked+0x483/0x600
 ? partition_sched_domains_locked+0xf0/0x600
 rebuild_sched_domains_locked+0x806/0xdc0
 update_partition_sd_lb+0x118/0x130
 cpuset_write_resmask+0xffc/0x1420
 cgroup_file_write+0xb2/0x290
 kernfs_fop_write_iter+0x194/0x290
 new_sync_write+0xeb/0x160
 vfs_write+0x16f/0x1d0
 ksys_write+0x81/0x180
 __x64_sys_write+0x21/0x30
 x64_sys_call+0x2f25/0x4630
 do_syscall_64+0x44/0xb0
 entry_SYSCALL_64_after_hwframe+0x78/0xe2
RIP: 0033:0x7f44a553c887

It can be reproduced with cammands:
cd /sys/fs/cgroup/
mkdir test
cd test/
echo +cpuset > ../cgroup.subtree_control
echo root > cpuset.cpus.partition
cat /sys/fs/cgroup/cpuset.cpus.effective
0-3
echo 0-3 > cpuset.cpus // taking away all cpus from root

This issue is caused by the incorrect rebuilding of scheduling domains.
In this scenario, test/cpuset.cpus.partition should be an invalid root
and should not trigger the rebuilding of scheduling domains. When calling
update_parent_effective_cpumask with partcmd_update, if newmask is not
null, it should recheck newmask whether there are cpus is available
for parect/cs that has tasks.

Statement: Red Hat believes this vulnerability to be of moderate severity because of the elevated privileges required to trigger the necessary conditions. Modifying cpuset settings typically requires root or admin access or a process must have   CAP_SYS_ADMIN permissions to configure cgroups.

Remediation:
For details on how to apply this update, which includes the changes described in this advisory, refer to:

https://access.redhat.com/articles/11258

The system must be rebooted for this update to take effect.