CVE-2021-46939

Advisory lineage Upstream: 0 Downstream: 11
Modified
Published: 27 Feb 2024, 18:40
Last modified:11 May 2026, 13:44

Vulnerability Summary

Overall Risk (default)
low
22/100
CVSS Score
5.5 MEDIUM
v3.1 (cve.org)
EPSS Score
0.01% LOW
0% probability 0.00%
KEV
Not listed
Ransomware
No reports
Public exploits
None found
Dark Web
Not detected

Timeline

27 Feb 2024, 18:40
Published
Vulnerability first disclosed
11 May 2026, 13:44
Last Modified
Vulnerability information updated

Description

In the Linux kernel, the following vulnerability has been resolved: tracing: Restructure trace_clock_global() to never block It was reported that a fix to the ring buffer recursion detection would cause a hung machine when performing suspend / resume testing. The following backtrace was extracted from debugging that case: Call Trace: trace_clock_global+0x91/0xa0 __rb_reserve_next+0x237/0x460 ring_buffer_lock_reserve+0x12a/0x3f0 trace_buffer_lock_reserve+0x10/0x50 __trace_graph_return+0x1f/0x80 trace_graph_return+0xb7/0xf0 ? trace_clock_global+0x91/0xa0 ftrace_return_to_handler+0x8b/0xf0 ? pv_hash+0xa0/0xa0 return_to_handler+0x15/0x30 ? ftrace_graph_caller+0xa0/0xa0 ? trace_clock_global+0x91/0xa0 ? __rb_reserve_next+0x237/0x460 ? ring_buffer_lock_reserve+0x12a/0x3f0 ? trace_event_buffer_lock_reserve+0x3c/0x120 ? trace_event_buffer_reserve+0x6b/0xc0 ? trace_event_raw_event_device_pm_callback_start+0x125/0x2d0 ? dpm_run_callback+0x3b/0xc0 ? pm_ops_is_empty+0x50/0x50 ? platform_get_irq_byname_optional+0x90/0x90 ? trace_device_pm_callback_start+0x82/0xd0 ? dpm_run_callback+0x49/0xc0 With the following RIP: RIP: 0010:native_queued_spin_lock_slowpath+0x69/0x200 Since the fix to the recursion detection would allow a single recursion to happen while tracing, this lead to the trace_clock_global() taking a spin lock and then trying to take it again: ring_buffer_lock_reserve() { trace_clock_global() { arch_spin_lock() { queued_spin_lock_slowpath() { /* lock taken */ (something else gets traced by function graph tracer) ring_buffer_lock_reserve() { trace_clock_global() { arch_spin_lock() { queued_spin_lock_slowpath() { /* DEAD LOCK! */ Tracing should *never* block, as it can lead to strange lockups like the above. Restructure the trace_clock_global() code to instead of simply taking a lock to update the recorded "prev_time" simply use it, as two events happening on two different CPUs that calls this at the same time, really doesn't matter which one goes first. Use a trylock to grab the lock for updating the prev_time, and if it fails, simply try again the next time. If it failed to be taken, that means something else is already updating it. Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=212761

CVSS Metrics

  • v3.1•MEDIUM•Score: 5.5CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

EPSS Trends

Current EPSS score: 0.01%• Percentile: 1%

Techniques & Countermeasures

  • CWE-662•Improper Synchronization

    The product utilizes multiple threads, processes, components, or systems to allow temporary access to a shared resource that can only be exclusive to one process at a time, but it does not properly synchronize these actions, which might cause simultaneous accesses of this resource by multiple threads or processes.

  • CWE-400•Uncontrolled Resource Consumption

    The product does not properly control the allocation and maintenance of a limited resource.

Affected Systems

  • linux•linux

    ≥ 14131f2f98ac350ee9e73faed916d2238a8b6a0d, < 91ca6f6a91f679c8645d7f3307e03ce86ad518c4 | ≥ 14131f2f98ac350ee9e73faed916d2238a8b6a0d, < 859b47a43f5a0e5b9a92b621dc6ceaad39fb5c8b | ≥ 14131f2f98ac350ee9e73faed916d2238a8b6a0d, < 1fca00920327be96f3318224f502e4d5460f9545 | ≥ 14131f2f98ac350ee9e73faed916d2238a8b6a0d, < d43d56dbf452ccecc1ec735cd4b6840118005d7c | ≥ 14131f2f98ac350ee9e73faed916d2238a8b6a0d, < c64da3294a7d59a4bf6874c664c13be892f15f44 | ≥ 14131f2f98ac350ee9e73faed916d2238a8b6a0d, < a33614d52e97fc8077eb0b292189ca7d964cc534 | ≥ 14131f2f98ac350ee9e73faed916d2238a8b6a0d, < 6e2418576228eeb12e7ba82edb8f9500623942ff | ≥ 14131f2f98ac350ee9e73faed916d2238a8b6a0d, < 2a1bd74b8186d7938bf004f5603f25b84785f63e | ≥ 14131f2f98ac350ee9e73faed916d2238a8b6a0d, < aafe104aa9096827a429bc1358f8260ee565b7cc | 2.6.30

  • linux•linux_kernel

    ≥ 2.6.30, < 4.4.269 | ≥ 4.5.0, < 4.9.269 | ≥ 4.10.0, < 4.14.233 | ≥ 4.15.0, < 4.19.191 | ≥ 4.20.0, < 5.4.118 | ≥ 5.5.0, < 5.10.36 | ≥ 5.11.0, < 5.11.20 | ≥ 5.12.0, < 5.12.3

References (9)