CVE-2022-50778 (GCVE-0-2022-50778)

Vulnerability from cvelistv5 – Published: 2025-12-24 13:06 – Updated: 2026-05-11 19:25
VLAI
Title
fortify: Fix __compiletime_strlen() under UBSAN_BOUNDS_LOCAL
Summary
In the Linux kernel, the following vulnerability has been resolved: fortify: Fix __compiletime_strlen() under UBSAN_BOUNDS_LOCAL With CONFIG_FORTIFY=y and CONFIG_UBSAN_LOCAL_BOUNDS=y enabled, we observe a runtime panic while running Android's Compatibility Test Suite's (CTS) android.hardware.input.cts.tests. This is stemming from a strlen() call in hidinput_allocate(). __compiletime_strlen() is implemented in terms of __builtin_object_size(), then does an array access to check for NUL-termination. A quirk of __builtin_object_size() is that for strings whose values are runtime dependent, __builtin_object_size(str, 1 or 0) returns the maximum size of possible values when those sizes are determinable at compile time. Example: static const char *v = "FOO BAR"; static const char *y = "FOO BA"; unsigned long x (int z) { // Returns 8, which is: // max(__builtin_object_size(v, 1), __builtin_object_size(y, 1)) return __builtin_object_size(z ? v : y, 1); } So when FORTIFY_SOURCE is enabled, the current implementation of __compiletime_strlen() will try to access beyond the end of y at runtime using the size of v. Mixed with UBSAN_LOCAL_BOUNDS we get a fault. hidinput_allocate() has a local C string whose value is control flow dependent on a switch statement, so __builtin_object_size(str, 1) evaluates to the maximum string length, making all other cases fault on the last character check. hidinput_allocate() could be cleaned up to avoid runtime calls to strlen() since the local variable can only have literal values, so there's no benefit to trying to fortify the strlen call site there. Perform a __builtin_constant_p() check against index 0 earlier in the macro to filter out the control-flow-dependant case. Add a KUnit test for checking the expected behavioral characteristics of FORTIFY_SOURCE internals.
Severity
No CVSS data available.
Assigner
Linux CNA under the mitre root
CNA scorecard D 53/100 over 6641 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 3009f891bb9f328945ebd5b71e12df7e2467f3dd , < ed42391164e6839a48aaf4c53eefda516835e799 (git)
Affected: 3009f891bb9f328945ebd5b71e12df7e2467f3dd , < 5d59ad2bfb35fccfe2ad5e8bb8801f6224d3f7d4 (git)
Affected: 3009f891bb9f328945ebd5b71e12df7e2467f3dd , < d07c0acb4f41cc42a0d97530946965b3e4fa68c1 (git)
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Linux Linux Affected: 5.16
Unaffected: 0 , < 5.16 (semver)
Unaffected: 5.19.17 , ≤ 5.19.* (semver)
Unaffected: 6.0.3 , ≤ 6.0.* (semver)
Unaffected: 6.1 , ≤ * (original_commit_for_fix)
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          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nfortify: Fix __compiletime_strlen() under UBSAN_BOUNDS_LOCAL\n\nWith CONFIG_FORTIFY=y and CONFIG_UBSAN_LOCAL_BOUNDS=y enabled, we observe\na runtime panic while running Android\u0027s Compatibility Test Suite\u0027s (CTS)\nandroid.hardware.input.cts.tests. This is stemming from a strlen()\ncall in hidinput_allocate().\n\n__compiletime_strlen() is implemented in terms of __builtin_object_size(),\nthen does an array access to check for NUL-termination. A quirk of\n__builtin_object_size() is that for strings whose values are runtime\ndependent, __builtin_object_size(str, 1 or 0) returns the maximum size\nof possible values when those sizes are determinable at compile time.\nExample:\n\n  static const char *v = \"FOO BAR\";\n  static const char *y = \"FOO BA\";\n  unsigned long x (int z) {\n      // Returns 8, which is:\n      // max(__builtin_object_size(v, 1), __builtin_object_size(y, 1))\n      return __builtin_object_size(z ? v : y, 1);\n  }\n\nSo when FORTIFY_SOURCE is enabled, the current implementation of\n__compiletime_strlen() will try to access beyond the end of y at runtime\nusing the size of v. Mixed with UBSAN_LOCAL_BOUNDS we get a fault.\n\nhidinput_allocate() has a local C string whose value is control flow\ndependent on a switch statement, so __builtin_object_size(str, 1)\nevaluates to the maximum string length, making all other cases fault on\nthe last character check. hidinput_allocate() could be cleaned up to\navoid runtime calls to strlen() since the local variable can only have\nliteral values, so there\u0027s no benefit to trying to fortify the strlen\ncall site there.\n\nPerform a __builtin_constant_p() check against index 0 earlier in the\nmacro to filter out the control-flow-dependant case. Add a KUnit test\nfor checking the expected behavioral characteristics of FORTIFY_SOURCE\ninternals."
        }
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          "url": "https://git.kernel.org/stable/c/d07c0acb4f41cc42a0d97530946965b3e4fa68c1"
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      "title": "fortify: Fix __compiletime_strlen() under UBSAN_BOUNDS_LOCAL",
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    "cveId": "CVE-2022-50778",
    "datePublished": "2025-12-24T13:06:07.182Z",
    "dateReserved": "2025-12-24T13:02:21.547Z",
    "dateUpdated": "2026-05-11T19:25:21.810Z",
    "state": "PUBLISHED"
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      "date": "2026-11-12",
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        "descriptions": [
          {
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            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nfortify: Fix __compiletime_strlen() under UBSAN_BOUNDS_LOCAL\n\nWith CONFIG_FORTIFY=y and CONFIG_UBSAN_LOCAL_BOUNDS=y enabled, we observe\na runtime panic while running Android\u0027s Compatibility Test Suite\u0027s (CTS)\nandroid.hardware.input.cts.tests. This is stemming from a strlen()\ncall in hidinput_allocate().\n\n__compiletime_strlen() is implemented in terms of __builtin_object_size(),\nthen does an array access to check for NUL-termination. A quirk of\n__builtin_object_size() is that for strings whose values are runtime\ndependent, __builtin_object_size(str, 1 or 0) returns the maximum size\nof possible values when those sizes are determinable at compile time.\nExample:\n\n  static const char *v = \"FOO BAR\";\n  static const char *y = \"FOO BA\";\n  unsigned long x (int z) {\n      // Returns 8, which is:\n      // max(__builtin_object_size(v, 1), __builtin_object_size(y, 1))\n      return __builtin_object_size(z ? v : y, 1);\n  }\n\nSo when FORTIFY_SOURCE is enabled, the current implementation of\n__compiletime_strlen() will try to access beyond the end of y at runtime\nusing the size of v. Mixed with UBSAN_LOCAL_BOUNDS we get a fault.\n\nhidinput_allocate() has a local C string whose value is control flow\ndependent on a switch statement, so __builtin_object_size(str, 1)\nevaluates to the maximum string length, making all other cases fault on\nthe last character check. hidinput_allocate() could be cleaned up to\navoid runtime calls to strlen() since the local variable can only have\nliteral values, so there\u0027s no benefit to trying to fortify the strlen\ncall site there.\n\nPerform a __builtin_constant_p() check against index 0 earlier in the\nmacro to filter out the control-flow-dependant case. Add a KUnit test\nfor checking the expected behavioral characteristics of FORTIFY_SOURCE\ninternals."
          },
          {
            "lang": "es",
            "value": "En el kernel de Linux, la siguiente vulnerabilidad ha sido resuelta:\n\nfortify: Correcci\u00f3n de __compiletime_strlen() bajo UBSAN_BOUNDS_LOCAL\n\nCon CONFIG_FORTIFY=y y CONFIG_UBSAN_LOCAL_BOUNDS=y habilitados, observamos un p\u00e1nico en tiempo de ejecuci\u00f3n mientras se ejecutan las pruebas android.hardware.input.cts.tests de la Suite de Pruebas de Compatibilidad (CTS) de Android. Esto se deriva de una llamada a strlen() en hidinput_allocate().\n\n__compiletime_strlen() se implementa en t\u00e9rminos de __builtin_object_size(), luego realiza un acceso a un array para verificar la terminaci\u00f3n NUL. Una peculiaridad de __builtin_object_size() es que para cadenas cuyos valores dependen del tiempo de ejecuci\u00f3n, __builtin_object_size(str, 1 o 0) devuelve el tama\u00f1o m\u00e1ximo de los valores posibles cuando esos tama\u00f1os son determinables en tiempo de compilaci\u00f3n. Ejemplo:\n\n  static const char v = \u201cFOO BAR\u201d;\n  static const char y = \u201cFOO BA\u201d;\n  unsigned long x (int z) {\n      // Devuelve 8, que es:\n      // max(__builtin_object_size(v, 1), __builtin_object_size(y, 1))\n      return __builtin_object_size(z ? v : y, 1);\n  }\n\nAs\u00ed, cuando FORTIFY_SOURCE est\u00e1 habilitado, la implementaci\u00f3n actual de __compiletime_strlen() intentar\u00e1 acceder m\u00e1s all\u00e1 del final de y en tiempo de ejecuci\u00f3n usando el tama\u00f1o de v. Mezclado con UBSAN_LOCAL_BOUNDS obtenemos un fallo.\n\nhidinput_allocate() tiene una cadena C local cuyo valor depende del flujo de control de una sentencia switch, por lo que __builtin_object_size(str, 1) se eval\u00faa a la longitud m\u00e1xima de la cadena, haciendo que todos los dem\u00e1s casos fallen en la comprobaci\u00f3n del \u00faltimo car\u00e1cter. hidinput_allocate() podr\u00eda limpiarse para evitar llamadas a strlen() en tiempo de ejecuci\u00f3n, ya que la variable local solo puede tener valores literales, por lo que no hay beneficio en intentar fortificar el sitio de llamada a strlen all\u00ed.\n\nRealizar una comprobaci\u00f3n __builtin_constant_p() contra el \u00edndice 0 antes en la macro para filtrar el caso dependiente del flujo de control. A\u00f1adir una prueba KUnit para comprobar las caracter\u00edsticas de comportamiento esperadas de los internos de FORTIFY_SOURCE."
          }
        ],
        "id": "CVE-2022-50778",
        "lastModified": "2026-11-10T12:10:00.177",
        "metrics": {},
        "published": "2025-12-24T13:16:04.640",
        "references": [
          {
            "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
            "url": "https://git.kernel.org/stable/c/5d59ad2bfb35fccfe2ad5e8bb8801f6224d3f7d4"
          },
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          }
        ],
        "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "vulnStatus": "Deferred"
      }
    },
    "redhat_vex": {
      "aggregate_severity": "Low",
      "current_release_date": "2026-11-06T13:02:44+00:00",
      "cve": "CVE-2022-50778",
      "id": "CVE-2022-50778",
      "initial_release_date": "2022-01-01T00:00:00+00:00",
      "product_status:fixed": "321",
      "product_status:known_affected": "38",
      "product_status:known_not_affected": "43",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: fortify: Fix __compiletime_strlen() under UBSAN_BOUNDS_LOCAL",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2022/cve-2022-50778.json",
      "version": "3"
    }
  }
}



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