fkie_cve-2021-47608
Vulnerability from fkie_nvd
Published
2024-06-19 15:15
Modified
2024-11-21 06:36
Severity ?
5.5 (Medium) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
Summary
In the Linux kernel, the following vulnerability has been resolved: bpf: Fix kernel address leakage in atomic fetch The change in commit 37086bfdc737 ("bpf: Propagate stack bounds to registers in atomics w/ BPF_FETCH") around check_mem_access() handling is buggy since this would allow for unprivileged users to leak kernel pointers. For example, an atomic fetch/and with -1 on a stack destination which holds a spilled pointer will migrate the spilled register type into a scalar, which can then be exported out of the program (since scalar != pointer) by dumping it into a map value. The original implementation of XADD was preventing this situation by using a double call to check_mem_access() one with BPF_READ and a subsequent one with BPF_WRITE, in both cases passing -1 as a placeholder value instead of register as per XADD semantics since it didn't contain a value fetch. The BPF_READ also included a check in check_stack_read_fixed_off() which rejects the program if the stack slot is of __is_pointer_value() if dst_regno < 0. The latter is to distinguish whether we're dealing with a regular stack spill/ fill or some arithmetical operation which is disallowed on non-scalars, see also 6e7e63cbb023 ("bpf: Forbid XADD on spilled pointers for unprivileged users") for more context on check_mem_access() and its handling of placeholder value -1. One minimally intrusive option to fix the leak is for the BPF_FETCH case to initially check the BPF_READ case via check_mem_access() with -1 as register, followed by the actual load case with non-negative load_reg to propagate stack bounds to registers.
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/423628125a484538111c2c6d9bb1588eb086053bPatch
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/7d3baf0afa3aa9102d6a521a8e4c41888bb79882Patch
af854a3a-2127-422b-91ae-364da2661108https://git.kernel.org/stable/c/423628125a484538111c2c6d9bb1588eb086053bPatch
af854a3a-2127-422b-91ae-364da2661108https://git.kernel.org/stable/c/7d3baf0afa3aa9102d6a521a8e4c41888bb79882Patch
Impacted products
Vendor Product Version
linux linux_kernel *
linux linux_kernel 5.16
linux linux_kernel 5.16
linux linux_kernel 5.16
linux linux_kernel 5.16
linux linux_kernel 5.16


To clipboard 

{
  "configurations": [
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              "versionEndExcluding": "5.15.11",
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  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Fix kernel address leakage in atomic fetch\n\nThe change in commit 37086bfdc737 (\"bpf: Propagate stack bounds to registers\nin atomics w/ BPF_FETCH\") around check_mem_access() handling is buggy since\nthis would allow for unprivileged users to leak kernel pointers. For example,\nan atomic fetch/and with -1 on a stack destination which holds a spilled\npointer will migrate the spilled register type into a scalar, which can then\nbe exported out of the program (since scalar != pointer) by dumping it into\na map value.\n\nThe original implementation of XADD was preventing this situation by using\na double call to check_mem_access() one with BPF_READ and a subsequent one\nwith BPF_WRITE, in both cases passing -1 as a placeholder value instead of\nregister as per XADD semantics since it didn\u0027t contain a value fetch. The\nBPF_READ also included a check in check_stack_read_fixed_off() which rejects\nthe program if the stack slot is of __is_pointer_value() if dst_regno \u003c 0.\nThe latter is to distinguish whether we\u0027re dealing with a regular stack spill/\nfill or some arithmetical operation which is disallowed on non-scalars, see\nalso 6e7e63cbb023 (\"bpf: Forbid XADD on spilled pointers for unprivileged\nusers\") for more context on check_mem_access() and its handling of placeholder\nvalue -1.\n\nOne minimally intrusive option to fix the leak is for the BPF_FETCH case to\ninitially check the BPF_READ case via check_mem_access() with -1 as register,\nfollowed by the actual load case with non-negative load_reg to propagate\nstack bounds to registers."
    },
    {
      "lang": "es",
      "value": "En el kernel de Linux, se resolvi\u00f3 la siguiente vulnerabilidad: bpf: corrige la fuga de la direcci\u00f3n del kernel en la recuperaci\u00f3n at\u00f3mica. El cambio en el commit 37086bfdc737 (\"bpf: propaga los l\u00edmites de la pila a los registros en at\u00f3micos con BPF_FETCH\") alrededor del manejo de check_mem_access() tiene errores ya que esto permitir\u00eda a usuarios sin privilegios filtrar punteros del kernel. Por ejemplo, una recuperaci\u00f3n at\u00f3mica/y con -1 en un destino de pila que contiene un puntero derramado migrar\u00e1 el tipo de registro derramado a un escalar, que luego se puede exportar fuera del programa (ya que escalar! = puntero) volc\u00e1ndolo en un valor de mapa. La implementaci\u00f3n original de XADD evitaba esta situaci\u00f3n mediante el uso de una llamada doble a check_mem_access(), una con BPF_READ y otra posterior con BPF_WRITE, en ambos casos pasando -1 como valor de marcador de posici\u00f3n en lugar de registrarse seg\u00fan la sem\u00e1ntica de XADD, ya que no lo hac\u00eda contener una recuperaci\u00f3n de valor. BPF_READ tambi\u00e9n incluy\u00f3 una verificaci\u00f3n en check_stack_read_fixed_off() que rechaza el programa si la ranura de la pila es de __is_pointer_value() si dst_regno \u0026lt; 0. Esto \u00faltimo es para distinguir si estamos tratando con un derrame/llenado de pila regular o alguna operaci\u00f3n aritm\u00e9tica que no est\u00e1 permitido en valores no escalares, consulte tambi\u00e9n 6e7e63cbb023 (\"bpf: Prohibir XADD en punteros dispersos para usuarios sin privilegios\") para obtener m\u00e1s contexto sobre check_mem_access() y su manejo del valor del marcador de posici\u00f3n -1. Una opci\u00f3n m\u00ednimamente intrusiva para solucionar la fuga es que el caso BPF_FETCH verifique inicialmente el caso BPF_READ mediante check_mem_access() con -1 como registro, seguido del caso de carga real con load_reg no negativo para propagar los l\u00edmites de la pila a los registros."
    }
  ],
  "id": "CVE-2021-47608",
  "lastModified": "2024-11-21T06:36:39.567",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "LOCAL",
          "availabilityImpact": "NONE",
          "baseScore": 5.5,
          "baseSeverity": "MEDIUM",
          "confidentialityImpact": "HIGH",
          "integrityImpact": "NONE",
          "privilegesRequired": "LOW",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N",
          "version": "3.1"
        },
        "exploitabilityScore": 1.8,
        "impactScore": 3.6,
        "source": "nvd@nist.gov",
        "type": "Primary"
      }
    ]
  },
  "published": "2024-06-19T15:15:55.360",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
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  "vulnStatus": "Modified",
  "weaknesses": [
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          "value": "NVD-CWE-noinfo"
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      ],
      "source": "nvd@nist.gov",
      "type": "Primary"
    }
  ]
}


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