{ "schemaVersion": 1, "attribution": [ { "source": "CISA Known Exploited Vulnerabilities", "url": "https://www.cisa.gov/known-exploited-vulnerabilities-catalog", "licence": "US government work" }, { "source": "GitHub Advisory Database", "url": "https://github.com/advisories", "licence": "CC BY 4.0" }, { "source": "Have I Been Pwned", "url": "https://haveibeenpwned.com/", "licence": "CC BY 4.0" }, { "source": "CVE Program (CVE records)", "url": "https://www.cve.org/Legal/TermsOfUse", "licence": "CVE Terms of Use", "notice": "Copyright © 1999-2026, The MITRE Corporation. CVE is a trademark and the CVE logo is a registered trademark of The MITRE Corporation.", "terms": "CVE Usage: MITRE hereby grants you a perpetual, worldwide, non-exclusive, no-charge, royalty-free, irrevocable copyright license to reproduce, prepare derivative works of, publicly display, publicly perform, sublicense, and distribute Common Vulnerabilities and Exposures (CVE™). Any copy you make for such purposes is authorized provided that you reproduce MITRE's copyright designation and this license in any such copy." }, { "source": "FIRST EPSS", "url": "https://www.first.org/epss/", "licence": "free to use; FIRST requests attribution" } ], "record": { "id": "CVE-2021-46939", "sourceURL": "https://www.cve.org/CVERecord?id=CVE-2021-46939", "idYear": 2021, "status": "PUBLISHED", "publishedAt": "2024-02-27T18:40:27.471Z", "updatedAt": "2026-05-11T13:44:49.866Z", "importedAt": "2026-10-24T01:56:36.661Z", "snapshot": { "id": "cve_2026-10-24_midnight_baseline", "at": "2026-10-24T00:00:00.000Z", "source": "https://github.com/CVEProject/cvelistV5/releases/tag/cve_2026-10-24_0100Z" }, "facts": { "title": "tracing: Restructure trace_clock_global() to never block", "summary": "In the Linux kernel, the following vulnerability has been resolved:\n\ntracing: Restructure trace_clock_global() to never block\n\nIt was reported that a fix to the ring buffer recursion detection would\ncause a hung machine when performing suspend / resume testing. The\nfollowing backtrace was extracted from debugging that case:\n\nCall Trace:\n trace_clock_global+0x91/0xa0\n __rb_reserve_next+0x237/0x460\n ring_buffer_lock_reserve+0x12a/0x3f0\n trace_buffer_lock_reserve+0x10/0x50\n __trace_graph_return+0x1f/0x80\n trace_graph_return+0xb7/0xf0\n ? trace_clock_global+0x91/0xa0\n ftrace_return_to_handler+0x8b/0xf0\n ? pv_hash+0xa0/0xa0\n return_to_handler+0x15/0x30\n ? ftrace_graph_caller+0xa0/0xa0\n ? trace_clock_global+0x91/0xa0\n ? __rb_reserve_next+0x237/0x460\n ? ring_buffer_lock_reserve+0x12a/0x3f0\n ? trace_event_buffer_lock_reserve+0x3c/0x120\n ? trace_event_buffer_reserve+0x6b/0xc0\n ? trace_event_raw_event_device_pm_callback_start+0x125/0x2d0\n ? dpm_run_callback+0x3b/0xc0\n ? pm_ops_is_empty+0x50/0x50\n ? platform_get_irq_byname_optional+0x90/0x90\n ? trace_device_pm_callback_start+0x82/0xd0\n ? dpm_run_callback+0x49/0xc0\n\nWith the following RIP:\n\nRIP: 0010:native_queued_spin_lock_slowpath+0x69/0x200\n\nSince the fix to the recursion detection would allow a single recursion to\nhappen while tracing, this lead to the trace_clock_global() taking a spin\nlock and then trying to take it again:\n\nring_buffer_lock_reserve() {\n trace_clock_global() {\n arch_spin_lock() {\n queued_spin_lock_slowpath() {\n /* lock taken */\n (something else gets traced by function graph tracer)\n ring_buffer_lock_reserve() {\n trace_clock_global() {\n arch_spin_lock() {\n queued_spin_lock_slowpath() {\n /* DEAD LOCK! */\n\nTracing should *never* block, as it can lead to strange lockups like the\nabove.\n\nRestructure the trace_clock_global() code to instead of simply taking a\nlock to update the recorded \"prev_time\" simply use it, as two events\nhappening on two different CPUs that calls this at the same time, really\ndoesn't matter which one goes first. Use a trylock to grab the lock for\nupdating the prev_time, and if it fails, simply try again the next time.\nIf it failed to be taken, that means something else is already updating\nit.\n\n\nBugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=212761", "affected": [ { "vendor": "Linux", "product": "Linux", "defaultStatus": "unaffected", "versions": [ { "version": "14131f2f98ac350ee9e73faed916d2238a8b6a0d", "status": "affected", "versionType": "git", "lessThan": "91ca6f6a91f679c8645d7f3307e03ce86ad518c4" }, { "version": "14131f2f98ac350ee9e73faed916d2238a8b6a0d", "status": "affected", "versionType": "git", "lessThan": "859b47a43f5a0e5b9a92b621dc6ceaad39fb5c8b" }, { "version": "14131f2f98ac350ee9e73faed916d2238a8b6a0d", "status": "affected", "versionType": "git", "lessThan": "1fca00920327be96f3318224f502e4d5460f9545" }, { "version": "14131f2f98ac350ee9e73faed916d2238a8b6a0d", "status": "affected", "versionType": "git", "lessThan": "d43d56dbf452ccecc1ec735cd4b6840118005d7c" }, { "version": "14131f2f98ac350ee9e73faed916d2238a8b6a0d", "status": "affected", "versionType": "git", "lessThan": "c64da3294a7d59a4bf6874c664c13be892f15f44" }, { "version": "14131f2f98ac350ee9e73faed916d2238a8b6a0d", "status": "affected", "versionType": "git", "lessThan": "a33614d52e97fc8077eb0b292189ca7d964cc534" }, { "version": "14131f2f98ac350ee9e73faed916d2238a8b6a0d", "status": "affected", "versionType": "git", "lessThan": "6e2418576228eeb12e7ba82edb8f9500623942ff" }, { "version": "14131f2f98ac350ee9e73faed916d2238a8b6a0d", "status": "affected", "versionType": "git", "lessThan": "2a1bd74b8186d7938bf004f5603f25b84785f63e" }, { "version": "14131f2f98ac350ee9e73faed916d2238a8b6a0d", "status": "affected", "versionType": "git", "lessThan": "aafe104aa9096827a429bc1358f8260ee565b7cc" } ] }, { "vendor": "Linux", "product": "Linux", "defaultStatus": "affected", "versions": [ { "version": "2.6.30", "status": "affected" }, { "version": "0", "status": "unaffected", "versionType": "semver", "lessThan": "2.6.30" }, { "version": "4.4.269", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "4.4.*" }, { "version": "4.9.269", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "4.9.*" }, { "version": "4.14.233", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "4.14.*" }, { "version": "4.19.191", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "4.19.*" }, { "version": "5.4.118", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "5.4.*" }, { "version": "5.10.36", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "5.10.*" }, { "version": "5.11.20", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "5.11.*" }, { "version": "5.12.3", "status": "unaffected", "versionType": "semver", "lessThanOrEqual": "5.12.*" }, { "version": "5.13", "status": "unaffected", "versionType": "original_commit_for_fix", "lessThanOrEqual": "*" } ] } ] } } }