medium CVSS 5.5 EPSS <0.1%

CVE-2021-47387·Kernel vulnerability

In the Linux kernel, the following vulnerability has been resolved: cpufreq: schedutil: Use kobject release() method to free sugov_tunables The struct sugov_tunables is protected by the kobject, so we can't free it directly. Otherwise we would get a call trace like this: ODEBUG: free active (active state 0) object type: timer_list hint: delayed_work_timer_fn+0x0/0x30 WARNING: CPU: 3 PID: 720 at lib/debugobjects.c:505 debug_print_object+0xb8/0x100 Modules linked in: CPU: 3 PID: 720 Comm: a.sh Tainted: G W 5.14.0-rc1-next-20210715-yocto-standard+ #507 Hardware name: Marvell OcteonTX CN96XX board (DT) pstate: 40400009 (nZcv daif +PAN -UAO -TCO BTYPE=--) pc : debug_print_object+0xb8/0x100 lr : debug_print_object+0xb8/0x100 sp : ffff80001ecaf910 x29: ffff80001ecaf910 x28: ffff00011b10b8d0 x27: ffff800011043d80 x26: ffff00011a8f0000 x25: ffff800013cb3ff0 x24: 0000000000000000 x23: ffff80001142aa68 x22: ffff800011043d80 x21: ffff00010de46f20 x20: ffff800013c0c520 x19: ffff800011d8f5b0 x18: 0000000000000010 x17: 6e6968207473696c x16: 5f72656d6974203a x15: 6570797420746365 x14: 6a626f2029302065 x13: 303378302f307830 x12: 2b6e665f72656d69 x11: ffff8000124b1560 x10: ffff800012331520 x9 : ffff8000100ca6b0 x8 : 000000000017ffe8 x7 : c0000000fffeffff x6 : 0000000000000001 x5 : ffff800011d8c000 x4 : ffff800011d8c740 x3 : 0000000000000000 x2 : ffff0001108301c0 x1 : ab3c90eedf9c0f00 x0 : 0000000000000000 Call trace: debug_print_object+0xb8/0x100 __debug_check_no_obj_freed+0x1c0/0x230 debug_check_no_obj_freed+0x20/0x88 slab_free_freelist_hook+0x154/0x1c8 kfree+0x114/0x5d0 sugov_exit+0xbc/0xc0 cpufreq_exit_governor+0x44/0x90 cpufreq_set_policy+0x268/0x4a8 store_scaling_governor+0xe0/0x128 store+0xc0/0xf0 sysfs_kf_write+0x54/0x80 kernfs_fop_write_iter+0x128/0x1c0 new_sync_write+0xf0/0x190 vfs_write+0x2d4/0x478 ksys_write+0x74/0x100 __arm64_sys_write+0x24/0x30 invoke_syscall.constprop.0+0x54/0xe0 do_el0_svc+0x64/0x158 el0_svc+0x2c/0xb0 el0t_64_sync_handler+0xb0/0xb8 el0t_64_sync+0x198/0x19c irq event stamp: 5518 hardirqs last enabled at (5517): [<ffff8000100cbd7c>] console_unlock+0x554/0x6c8 hardirqs last disabled at (5518): [<ffff800010fc0638>] el1_dbg+0x28/0xa0 softirqs last enabled at (5504): [<ffff8000100106e0>] __do_softirq+0x4d0/0x6c0 softirqs last disabled at (5483): [<ffff800010049548>] irq_exit+0x1b0/0x1b8 So split the original sugov_tunables_free() into two functions, sugov_clear_global_tunables() is just used to clear the global_tunables and the new sugov_tunables_free() is used as kobj_type::release to release the sugov_tunables safely.

Severity
medium
Software
Kernel
Fixed in
5.14.10
Published

How likely is exploitation

FIRST's Exploit Prediction Scoring System puts the probability of this CVE being exploited in the next 30 days at <0.1% — in the bottom 1% of all published CVEs. EPSS is an independent forecast of exploitation, not a severity rating: it says nothing about how much damage a successful attack does, which is what a CVSS score measures.

Affected versions

From: 5.11

Until: 5.14.10

Fixed in: 5.14.10

How to fix this CVE

Update your Linux kernel to version 5.14.10 or later to resolve a memory management issue in the CPU frequency scaling scheduler utility governor. This vulnerability affects the improper deallocation of tunable parameters, which can trigger kernel warnings and system instability. Apply the kernel update through your distribution's package manager and reboot your system to complete the remediation.

sudo dnf update kernel && sudo reboot

Defensia detects this vulnerability

How to check if you are affected

  1. Check your current kernel version: uname -r
  2. Verify if kernel version is 5.11.x through 5.14.9: if [[ $(uname -r | cut -d. -f1-2) == '5.11' ]] || [[ $(uname -r | cut -d. -f1-2) == '5.12' ]] || [[ $(uname -r | cut -d. -f1-2) == '5.13' ]] || [[ $(uname -r | cut -d. -f1-2) == '5.14' && $(uname -r | cut -d. -f3) -lt 10 ]]; then echo 'VULNERABLE'; fi
  3. Search kernel logs for the specific debug object error: dmesg | grep -i 'ODEBUG: free active' | grep -i 'timer_list'
  4. Confirm the fix by verifying kernel version after reboot: uname -r should show 5.14.10 or later

FAQ

What is CVE-2021-47387?

This vulnerability exists in the Linux kernel's CPU frequency scaling (cpufreq) scheduler utility governor where the sugov_tunables structure was freed directly instead of through the proper kobject release mechanism. This violation of kernel memory management rules causes debug object warnings and potential system instability.

Is CVE-2021-47387 being actively exploited?

No, this vulnerability is not listed in CISA's Known Exploited Vulnerabilities catalog and no public exploits are available. The issue is a kernel memory handling defect rather than a remotely exploitable security flaw.

What versions of Kernel are affected by CVE-2021-47387?

Linux kernel versions 5.11.0 through 5.14.9 are vulnerable. The vulnerability was patched in kernel version 5.14.10 and later.

How do I check if my server is vulnerable to CVE-2021-47387?

Run 'uname -r' to display your kernel version. If the output shows version 5.11.x, 5.12.x, 5.13.x, or 5.14.0-5.14.9, your system is vulnerable and requires a kernel update.

Does Defensia detect CVE-2021-47387?

Yes — Defensia's CVE advisory scanner compares installed package versions against the NVD database. If the Linux kernel is installed on a monitored server, CVE-2021-47387 will appear in your dashboard with remediation steps.

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References

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