fkie_cve-2022-50778
Vulnerability from fkie_nvd
Published
2025-12-24 13:16
Modified
2025-12-24 13:16
Severity ?
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.
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/5d59ad2bfb35fccfe2ad5e8bb8801f6224d3f7d4
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/d07c0acb4f41cc42a0d97530946965b3e4fa68c1
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/ed42391164e6839a48aaf4c53eefda516835e799
Impacted products
Vendor Product Version


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{
  "cveTags": [],
  "descriptions": [
    {
      "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."
    }
  ],
  "id": "CVE-2022-50778",
  "lastModified": "2025-12-24T13:16:04.640",
  "metrics": {},
  "published": "2025-12-24T13:16:04.640",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/5d59ad2bfb35fccfe2ad5e8bb8801f6224d3f7d4"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/d07c0acb4f41cc42a0d97530946965b3e4fa68c1"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/ed42391164e6839a48aaf4c53eefda516835e799"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Received"
}


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