CVE-2026-23316 (GCVE-0-2026-23316)

Vulnerability from cvelistv5 – Published: 2026-03-25 10:27 – Updated: 2026-04-13 06:04
VLAI?
Title
net: ipv4: fix ARM64 alignment fault in multipath hash seed
Summary
In the Linux kernel, the following vulnerability has been resolved: net: ipv4: fix ARM64 alignment fault in multipath hash seed `struct sysctl_fib_multipath_hash_seed` contains two u32 fields (user_seed and mp_seed), making it an 8-byte structure with a 4-byte alignment requirement. In `fib_multipath_hash_from_keys()`, the code evaluates the entire struct atomically via `READ_ONCE()`: mp_seed = READ_ONCE(net->ipv4.sysctl_fib_multipath_hash_seed).mp_seed; While this silently works on GCC by falling back to unaligned regular loads which the ARM64 kernel tolerates, it causes a fatal kernel panic when compiled with Clang and LTO enabled. Commit e35123d83ee3 ("arm64: lto: Strengthen READ_ONCE() to acquire when CONFIG_LTO=y") strengthens `READ_ONCE()` to use Load-Acquire instructions (`ldar` / `ldapr`) to prevent compiler reordering bugs under Clang LTO. Since the macro evaluates the full 8-byte struct, Clang emits a 64-bit `ldar` instruction. ARM64 architecture strictly requires `ldar` to be naturally aligned, thus executing it on a 4-byte aligned address triggers a strict Alignment Fault (FSC = 0x21). Fix the read side by moving the `READ_ONCE()` directly to the `u32` member, which emits a safe 32-bit `ldar Wn`. Furthermore, Eric Dumazet pointed out that `WRITE_ONCE()` on the entire struct in `proc_fib_multipath_hash_set_seed()` is also flawed. Analysis shows that Clang splits this 8-byte write into two separate 32-bit `str` instructions. While this avoids an alignment fault, it destroys atomicity and exposes a tear-write vulnerability. Fix this by explicitly splitting the write into two 32-bit `WRITE_ONCE()` operations. Finally, add the missing `READ_ONCE()` when reading `user_seed` in `proc_fib_multipath_hash_seed()` to ensure proper pairing and concurrency safety.
Severity ?
No CVSS data available.
Assigner
References
Impacted products
Vendor Product Version
Linux Linux Affected: 4ee2a8cace3fb9a34aea6a56426f89d26dd514f3 , < 4bdc94d45d5459f0149085dfc1efe733c8e14f11 (git)
Affected: 4ee2a8cace3fb9a34aea6a56426f89d26dd514f3 , < 7e4ad34a8889a6a9e0f6cc7c55d02161fe31a199 (git)
Affected: 4ee2a8cace3fb9a34aea6a56426f89d26dd514f3 , < 607e923a3c1b2120de430b3dcde25ed8ad213c0a (git)
Affected: 4ee2a8cace3fb9a34aea6a56426f89d26dd514f3 , < 4ee7fa6cf78ff26d783d39e2949d14c4c1cd5e7f (git)
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    Linux Linux Affected: 6.11
Unaffected: 0 , < 6.11 (semver)
Unaffected: 6.12.77 , ≤ 6.12.* (semver)
Unaffected: 6.18.17 , ≤ 6.18.* (semver)
Unaffected: 6.19.7 , ≤ 6.19.* (semver)
Unaffected: 7.0 , ≤ * (original_commit_for_fix)
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet: ipv4: fix ARM64 alignment fault in multipath hash seed\n\n`struct sysctl_fib_multipath_hash_seed` contains two u32 fields\n(user_seed and mp_seed), making it an 8-byte structure with a 4-byte\nalignment requirement.\n\nIn `fib_multipath_hash_from_keys()`, the code evaluates the entire\nstruct atomically via `READ_ONCE()`:\n\n    mp_seed = READ_ONCE(net-\u003eipv4.sysctl_fib_multipath_hash_seed).mp_seed;\n\nWhile this silently works on GCC by falling back to unaligned regular\nloads which the ARM64 kernel tolerates, it causes a fatal kernel panic\nwhen compiled with Clang and LTO enabled.\n\nCommit e35123d83ee3 (\"arm64: lto: Strengthen READ_ONCE() to acquire\nwhen CONFIG_LTO=y\") strengthens `READ_ONCE()` to use Load-Acquire\ninstructions (`ldar` / `ldapr`) to prevent compiler reordering bugs\nunder Clang LTO. Since the macro evaluates the full 8-byte struct,\nClang emits a 64-bit `ldar` instruction. ARM64 architecture strictly\nrequires `ldar` to be naturally aligned, thus executing it on a 4-byte\naligned address triggers a strict Alignment Fault (FSC = 0x21).\n\nFix the read side by moving the `READ_ONCE()` directly to the `u32`\nmember, which emits a safe 32-bit `ldar Wn`.\n\nFurthermore, Eric Dumazet pointed out that `WRITE_ONCE()` on the entire\nstruct in `proc_fib_multipath_hash_set_seed()` is also flawed. Analysis\nshows that Clang splits this 8-byte write into two separate 32-bit\n`str` instructions. While this avoids an alignment fault, it destroys\natomicity and exposes a tear-write vulnerability. Fix this by\nexplicitly splitting the write into two 32-bit `WRITE_ONCE()`\noperations.\n\nFinally, add the missing `READ_ONCE()` when reading `user_seed` in\n`proc_fib_multipath_hash_seed()` to ensure proper pairing and\nconcurrency safety."
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        "dateUpdated": "2026-04-13T06:04:15.316Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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        {
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      "date": "2026-05-09",
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    },
    "nvd": "{\"cve\":{\"id\":\"CVE-2026-23316\",\"sourceIdentifier\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"published\":\"2026-03-25T11:16:28.063\",\"lastModified\":\"2026-04-23T21:07:02.380\",\"vulnStatus\":\"Analyzed\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"In the Linux kernel, the following vulnerability has been resolved:\\n\\nnet: ipv4: fix ARM64 alignment fault in multipath hash seed\\n\\n`struct sysctl_fib_multipath_hash_seed` contains two u32 fields\\n(user_seed and mp_seed), making it an 8-byte structure with a 4-byte\\nalignment requirement.\\n\\nIn `fib_multipath_hash_from_keys()`, the code evaluates the entire\\nstruct atomically via `READ_ONCE()`:\\n\\n    mp_seed = READ_ONCE(net-\u003eipv4.sysctl_fib_multipath_hash_seed).mp_seed;\\n\\nWhile this silently works on GCC by falling back to unaligned regular\\nloads which the ARM64 kernel tolerates, it causes a fatal kernel panic\\nwhen compiled with Clang and LTO enabled.\\n\\nCommit e35123d83ee3 (\\\"arm64: lto: Strengthen READ_ONCE() to acquire\\nwhen CONFIG_LTO=y\\\") strengthens `READ_ONCE()` to use Load-Acquire\\ninstructions (`ldar` / `ldapr`) to prevent compiler reordering bugs\\nunder Clang LTO. Since the macro evaluates the full 8-byte struct,\\nClang emits a 64-bit `ldar` instruction. ARM64 architecture strictly\\nrequires `ldar` to be naturally aligned, thus executing it on a 4-byte\\naligned address triggers a strict Alignment Fault (FSC = 0x21).\\n\\nFix the read side by moving the `READ_ONCE()` directly to the `u32`\\nmember, which emits a safe 32-bit `ldar Wn`.\\n\\nFurthermore, Eric Dumazet pointed out that `WRITE_ONCE()` on the entire\\nstruct in `proc_fib_multipath_hash_set_seed()` is also flawed. Analysis\\nshows that Clang splits this 8-byte write into two separate 32-bit\\n`str` instructions. While this avoids an alignment fault, it destroys\\natomicity and exposes a tear-write vulnerability. Fix this by\\nexplicitly splitting the write into two 32-bit `WRITE_ONCE()`\\noperations.\\n\\nFinally, add the missing `READ_ONCE()` when reading `user_seed` in\\n`proc_fib_multipath_hash_seed()` to ensure proper pairing and\\nconcurrency safety.\"},{\"lang\":\"es\",\"value\":\"En el kernel de Linux, la siguiente vulnerabilidad ha sido resuelta:\\n\\nnet: ipv4: solucionar fallo de alineaci\u00f3n ARM64 en la semilla de hash multipath\\n\\n\u0027struct sysctl_fib_multipath_hash_seed\u0027 contiene dos campos u32 (user_seed y mp_seed), convirti\u00e9ndola en una estructura de 8 bytes con un requisito de alineaci\u00f3n de 4 bytes.\\n\\nEn \u0027fib_multipath_hash_from_keys()\u0027, el c\u00f3digo eval\u00faa la estructura completa at\u00f3micamente a trav\u00e9s de \u0027READ_ONCE()\u0027:\\n\\n    mp_seed = \u0027READ_ONCE\u0027(net-\u0026gt;ipv4.sysctl_fib_multipath_hash_seed).mp_seed;\\n\\nAunque esto funciona silenciosamente en GCC al recurrir a cargas regulares no alineadas que el kernel ARM64 tolera, causa un p\u00e1nico fatal del kernel cuando se compila con Clang y LTO habilitado.\\n\\nEl commit e35123d83ee3 (\u0027arm64: lto: Strengthen \u0027READ_ONCE()\u0027 to acquire when CONFIG_LTO=y\u0027) refuerza \u0027READ_ONCE()\u0027 para usar instrucciones Load-Acquire (\u0027ldar\u0027 / \u0027ldapr\u0027) para prevenir errores de reordenamiento del compilador bajo Clang LTO. Dado que la macro eval\u00faa la estructura completa de 8 bytes, Clang emite una instrucci\u00f3n \u0027ldar\u0027 de 64 bits. La arquitectura ARM64 requiere estrictamente que \u0027ldar\u0027 est\u00e9 naturalmente alineado, por lo tanto, ejecutarlo en una direcci\u00f3n alineada a 4 bytes desencadena un fallo de alineaci\u00f3n estricto (FSC = 0x21).\\n\\nSolucionar el lado de lectura moviendo \u0027READ_ONCE()\u0027 directamente al miembro \u0027u32\u0027, lo que emite un \u0027ldar Wn\u0027 seguro de 32 bits.\\n\\nAdem\u00e1s, Eric Dumazet se\u00f1al\u00f3 que \u0027WRITE_ONCE()\u0027 en la estructura completa en \u0027proc_fib_multipath_hash_set_seed()\u0027 tambi\u00e9n es defectuoso. El an\u00e1lisis muestra que Clang divide esta escritura de 8 bytes en dos instrucciones \u0027str\u0027 separadas de 32 bits. Aunque esto evita un fallo de alineaci\u00f3n, destruye la atomicidad y expone una vulnerabilidad de escritura fragmentada. Solucionar esto dividiendo expl\u00edcitamente la escritura en dos operaciones \u0027WRITE_ONCE()\u0027 de 32 bits.\\n\\nFinalmente, a\u00f1adir el \u0027READ_ONCE()\u0027 faltante al leer \u0027user_seed\u0027 en \u0027proc_fib_multipath_hash_seed()\u0027 para asegurar un emparejamiento adecuado y seguridad de concurrencia.\"}],\"metrics\":{\"cvssMetricV31\":[{\"source\":\"nvd@nist.gov\",\"type\":\"Primary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H\",\"baseScore\":5.5,\"baseSeverity\":\"MEDIUM\",\"attackVector\":\"LOCAL\",\"attackComplexity\":\"LOW\",\"privilegesRequired\":\"LOW\",\"userInteraction\":\"NONE\",\"scope\":\"UNCHANGED\",\"confidentialityImpact\":\"NONE\",\"integrityImpact\":\"NONE\",\"availabilityImpact\":\"HIGH\"},\"exploitabilityScore\":1.8,\"impactScore\":3.6}]},\"weaknesses\":[{\"source\":\"nvd@nist.gov\",\"type\":\"Primary\",\"description\":[{\"lang\":\"en\",\"value\":\"NVD-CWE-noinfo\"}]}],\"configurations\":[{\"nodes\":[{\"operator\":\"OR\",\"negate\":false,\"cpeMatch\":[{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\",\"versionStartIncluding\":\"6.11.1\",\"versionEndExcluding\":\"6.12.77\",\"matchCriteriaId\":\"A9108695-408B-4C1A-A58A-9B59404F6DEE\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\",\"versionStartIncluding\":\"6.13\",\"versionEndExcluding\":\"6.18.17\",\"matchCriteriaId\":\"A5E006E4-59C7-43C1-9231-62A72219F2BA\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*\",\"versionStartIncluding\":\"6.19\",\"versionEndExcluding\":\"6.19.7\",\"matchCriteriaId\":\"69245D10-0B71-485E-80C3-A64F077004D3\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:6.11:-:*:*:*:*:*:*\",\"matchCriteriaId\":\"4770BA57-3F3F-493B-8608-EC3B25254949\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:7.0:rc1:*:*:*:*:*:*\",\"matchCriteriaId\":\"F253B622-8837-4245-BCE5-A7BF8FC76A16\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:7.0:rc2:*:*:*:*:*:*\",\"matchCriteriaId\":\"4AE85AD8-4641-4E7C-A2F4-305E2CD9EE64\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:7.0:rc3:*:*:*:*:*:*\",\"matchCriteriaId\":\"F666C8D8-6538-46D4-B318-87610DE64C34\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:7.0:rc4:*:*:*:*:*:*\",\"matchCriteriaId\":\"02259FDA-961B-47BC-AE7F-93D7EC6E90C2\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:7.0:rc5:*:*:*:*:*:*\",\"matchCriteriaId\":\"58A9FEFF-C040-420D-8F0A-BFDAAA1DF258\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:7.0:rc6:*:*:*:*:*:*\",\"matchCriteriaId\":\"1D2315C0-D46F-4F85-9754-F9E5E11374A6\"},{\"vulnerable\":true,\"criteria\":\"cpe:2.3:o:linux:linux_kernel:7.0:rc7:*:*:*:*:*:*\",\"matchCriteriaId\":\"512EE3A8-A590-4501-9A94-5D4B268D6138\"}]}]}],\"references\":[{\"url\":\"https://git.kernel.org/stable/c/4bdc94d45d5459f0149085dfc1efe733c8e14f11\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"tags\":[\"Patch\"]},{\"url\":\"https://git.kernel.org/stable/c/4ee7fa6cf78ff26d783d39e2949d14c4c1cd5e7f\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"tags\":[\"Patch\"]},{\"url\":\"https://git.kernel.org/stable/c/607e923a3c1b2120de430b3dcde25ed8ad213c0a\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"tags\":[\"Patch\"]},{\"url\":\"https://git.kernel.org/stable/c/7e4ad34a8889a6a9e0f6cc7c55d02161fe31a199\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"tags\":[\"Patch\"]}]}}"
  }
}


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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

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Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



Detection rules are retrieved from Rulezet.