Deadlock Affecting kernel-debug package, versions *
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-CENTOS7-KERNELDEBUG-6302248
- published28 Feb 2024
- disclosed27 Feb 2024
Introduced: 27 Feb 2024
CVE-2021-46939 (opens in a new tab)How to fix?
There is no fixed version for Centos:7 kernel-debug.
NVD Description
Note: Versions mentioned in the description apply only to the upstream kernel-debug package and not the kernel-debug package as distributed by Centos.
See How to fix? for Centos:7 relevant fixed versions and status.
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
References
- https://access.redhat.com/security/cve/CVE-2021-46939
- https://git.kernel.org/stable/c/1fca00920327be96f3318224f502e4d5460f9545
- https://git.kernel.org/stable/c/2a1bd74b8186d7938bf004f5603f25b84785f63e
- https://git.kernel.org/stable/c/6e2418576228eeb12e7ba82edb8f9500623942ff
- https://git.kernel.org/stable/c/859b47a43f5a0e5b9a92b621dc6ceaad39fb5c8b
- https://git.kernel.org/stable/c/91ca6f6a91f679c8645d7f3307e03ce86ad518c4
- https://git.kernel.org/stable/c/a33614d52e97fc8077eb0b292189ca7d964cc534
- https://git.kernel.org/stable/c/aafe104aa9096827a429bc1358f8260ee565b7cc
- https://git.kernel.org/stable/c/c64da3294a7d59a4bf6874c664c13be892f15f44
- https://git.kernel.org/stable/c/d43d56dbf452ccecc1ec735cd4b6840118005d7c