CVE-2024-49866 Information

Nov 01, 2024 cve

Description

In the Linux kernel the following vulnerability has been resolved:

tracing/timerlat: Fix a race during cpuhp processing

There is another found exception that the imerlat/1\ thread was scheduled on CPU0 and lead to timer corruption finally:

ODEBUG: init active (active state 0) object: ffff888237c2e108 object type: hrtimer hint: timerlat_irq+0x0/0x220
WARNING: CPU: 0 PID: 426 at lib/debugobjects.c:518 debug_print_object+0x7d/0xb0
Modules linked in:
CPU: 0 UID: 0 PID: 426 Comm: timerlat/1 Not tainted 6.11.0-rc7+ 45
Hardware name: QEMU Standard PC (i440FX + PIIX 1996) BIOS 1.13.0-1ubuntu1.1 04/01/2014
RIP: 0010:debug_print_object+0x7d/0xb0
...
Call Trace:
 <TASK>
 ? __warn+0x7c/0x110
 ? debug_print_object+0x7d/0xb0
 ? report_bug+0xf1/0x1d0
 ? prb_read_valid+0x17/0x20
 ? handle_bug+0x3f/0x70
 ? exc_invalid_op+0x13/0x60
 ? asm_exc_invalid_op+0x16/0x20
 ? debug_print_object+0x7d/0xb0
 ? debug_print_object+0x7d/0xb0
 ? __pfx_timerlat_irq+0x10/0x10
 __debug_object_init+0x110/0x150
 hrtimer_init+0x1d/0x60
 timerlat_main+0xab/0x2d0
 ? __pfx_timerlat_main+0x10/0x10
 kthread+0xb7/0xe0
 ? __pfx_kthread+0x10/0x10
 ret_from_fork+0x2d/0x40
 ? __pfx_kthread+0x10/0x10
 ret_from_fork_asm+0x1a/0x30
 </TASK>

After tracing the scheduling event it was discovered that the migration of the imerlat/1\ thread was performed during thread creation. Further analysis confirmed that it is because the CPU online processing for osnoise is implemented through workers which is asynchronous with the offline processing. When the worker was scheduled to create a thread the CPU may has already been removed from the cpu_online_mask during the offline process resulting in the inability to select the right CPU:

T1 | T2 [CPUHP_ONLINE] | cpu_device_down() osnoise_hotplug_workfn() | | cpus_write_lock() | takedown_cpu(1) | cpus_write_unlock() [CPUHP_OFFLINE] | cpus_read_lock() | start_kthread(1) | cpus_read_unlock() |

To fix this skip online processing if the CPU is already offline.

Reference

https://git.kernel.org/stable/c/322920b53dc11f9c2b33397eb3ae5bc6a175b60d https://git.kernel.org/stable/c/ce25f33ba89d6eefef64157655d318444580fa14 https://git.kernel.org/stable/c/a6e9849063a6c8f4cb2f652a437e44e3ed24356c https://git.kernel.org/stable/c/a0d9c0cd5856191e095cf43a2e141b73945b7716 https://git.kernel.org/stable/c/f72b451dc75578f644a3019c1489e9ae2c14e6c4 https://git.kernel.org/stable/c/829e0c9f0855f26b3ae830d17b24aec103f7e915

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