CVE-2025-38591 (GCVE-0-2025-38591)
Vulnerability from cvelistv5
Published
2025-08-19 17:03
Modified
2025-08-19 17:03
Severity ?
Summary
In the Linux kernel, the following vulnerability has been resolved: bpf: Reject narrower access to pointer ctx fields The following BPF program, simplified from a syzkaller repro, causes a kernel warning: r0 = *(u8 *)(r1 + 169); exit; With pointer field sk being at offset 168 in __sk_buff. This access is detected as a narrower read in bpf_skb_is_valid_access because it doesn't match offsetof(struct __sk_buff, sk). It is therefore allowed and later proceeds to bpf_convert_ctx_access. Note that for the "is_narrower_load" case in the convert_ctx_accesses(), the insn->off is aligned, so the cnt may not be 0 because it matches the offsetof(struct __sk_buff, sk) in the bpf_convert_ctx_access. However, the target_size stays 0 and the verifier errors with a kernel warning: verifier bug: error during ctx access conversion(1) This patch fixes that to return a proper "invalid bpf_context access off=X size=Y" error on the load instruction. The same issue affects multiple other fields in context structures that allow narrow access. Some other non-affected fields (for sk_msg, sk_lookup, and sockopt) were also changed to use bpf_ctx_range_ptr for consistency. Note this syzkaller crash was reported in the "Closes" link below, which used to be about a different bug, fixed in commit fce7bd8e385a ("bpf/verifier: Handle BPF_LOAD_ACQ instructions in insn_def_regno()"). Because syzbot somehow confused the two bugs, the new crash and repro didn't get reported to the mailing list.
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/202900ceeef67458c964c2af6e1427c8e533ea7c
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/e09299225d5ba3916c91ef70565f7d2187e4cca0
Impacted products
Vendor Product Version
Linux Linux Version: f96da09473b52c09125cc9bf7d7d4576ae8229e0
Version: f96da09473b52c09125cc9bf7d7d4576ae8229e0
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   Linux Linux Version: 4.13
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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "kernel/bpf/cgroup.c",
            "net/core/filter.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
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              "status": "affected",
              "version": "f96da09473b52c09125cc9bf7d7d4576ae8229e0",
              "versionType": "git"
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            {
              "lessThan": "e09299225d5ba3916c91ef70565f7d2187e4cca0",
              "status": "affected",
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              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "kernel/bpf/cgroup.c",
            "net/core/filter.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "4.13"
            },
            {
              "lessThan": "4.13",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.16.*",
              "status": "unaffected",
              "version": "6.16.1",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "6.17-rc1",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.16.1",
                  "versionStartIncluding": "4.13",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.17-rc1",
                  "versionStartIncluding": "4.13",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Reject narrower access to pointer ctx fields\n\nThe following BPF program, simplified from a syzkaller repro, causes a\nkernel warning:\n\n    r0 = *(u8 *)(r1 + 169);\n    exit;\n\nWith pointer field sk being at offset 168 in __sk_buff. This access is\ndetected as a narrower read in bpf_skb_is_valid_access because it\ndoesn\u0027t match offsetof(struct __sk_buff, sk). It is therefore allowed\nand later proceeds to bpf_convert_ctx_access. Note that for the\n\"is_narrower_load\" case in the convert_ctx_accesses(), the insn-\u003eoff\nis aligned, so the cnt may not be 0 because it matches the\noffsetof(struct __sk_buff, sk) in the bpf_convert_ctx_access. However,\nthe target_size stays 0 and the verifier errors with a kernel warning:\n\n    verifier bug: error during ctx access conversion(1)\n\nThis patch fixes that to return a proper \"invalid bpf_context access\noff=X size=Y\" error on the load instruction.\n\nThe same issue affects multiple other fields in context structures that\nallow narrow access. Some other non-affected fields (for sk_msg,\nsk_lookup, and sockopt) were also changed to use bpf_ctx_range_ptr for\nconsistency.\n\nNote this syzkaller crash was reported in the \"Closes\" link below, which\nused to be about a different bug, fixed in\ncommit fce7bd8e385a (\"bpf/verifier: Handle BPF_LOAD_ACQ instructions\nin insn_def_regno()\"). Because syzbot somehow confused the two bugs,\nthe new crash and repro didn\u0027t get reported to the mailing list."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2025-08-19T17:03:12.508Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/202900ceeef67458c964c2af6e1427c8e533ea7c"
        },
        {
          "url": "https://git.kernel.org/stable/c/e09299225d5ba3916c91ef70565f7d2187e4cca0"
        }
      ],
      "title": "bpf: Reject narrower access to pointer ctx fields",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2025-38591",
    "datePublished": "2025-08-19T17:03:12.508Z",
    "dateReserved": "2025-04-16T04:51:24.026Z",
    "dateUpdated": "2025-08-19T17:03:12.508Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.1",
  "vulnerability-lookup:meta": {
    "nvd": "{\"cve\":{\"id\":\"CVE-2025-38591\",\"sourceIdentifier\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"published\":\"2025-08-19T17:15:36.790\",\"lastModified\":\"2025-08-20T14:40:17.713\",\"vulnStatus\":\"Awaiting Analysis\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"In the Linux kernel, the following vulnerability has been resolved:\\n\\nbpf: Reject narrower access to pointer ctx fields\\n\\nThe following BPF program, simplified from a syzkaller repro, causes a\\nkernel warning:\\n\\n    r0 = *(u8 *)(r1 + 169);\\n    exit;\\n\\nWith pointer field sk being at offset 168 in __sk_buff. This access is\\ndetected as a narrower read in bpf_skb_is_valid_access because it\\ndoesn\u0027t match offsetof(struct __sk_buff, sk). It is therefore allowed\\nand later proceeds to bpf_convert_ctx_access. Note that for the\\n\\\"is_narrower_load\\\" case in the convert_ctx_accesses(), the insn-\u003eoff\\nis aligned, so the cnt may not be 0 because it matches the\\noffsetof(struct __sk_buff, sk) in the bpf_convert_ctx_access. However,\\nthe target_size stays 0 and the verifier errors with a kernel warning:\\n\\n    verifier bug: error during ctx access conversion(1)\\n\\nThis patch fixes that to return a proper \\\"invalid bpf_context access\\noff=X size=Y\\\" error on the load instruction.\\n\\nThe same issue affects multiple other fields in context structures that\\nallow narrow access. Some other non-affected fields (for sk_msg,\\nsk_lookup, and sockopt) were also changed to use bpf_ctx_range_ptr for\\nconsistency.\\n\\nNote this syzkaller crash was reported in the \\\"Closes\\\" link below, which\\nused to be about a different bug, fixed in\\ncommit fce7bd8e385a (\\\"bpf/verifier: Handle BPF_LOAD_ACQ instructions\\nin insn_def_regno()\\\"). Because syzbot somehow confused the two bugs,\\nthe new crash and repro didn\u0027t get reported to the mailing list.\"},{\"lang\":\"es\",\"value\":\"En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: bpf: Rechazo de acceso m\u00e1s estrecho a campos de puntero ctx. El siguiente programa BPF, simplificado a partir de una reproducci\u00f3n de syzkaller, genera una advertencia del kernel: r0 = *(u8 *)(r1 + 169); exit; Con el campo de puntero sk en el desplazamiento 168 en __sk_buff. Este acceso se detecta como una lectura m\u00e1s estrecha en bpf_skb_is_valid_access porque no coincide con offsetof(struct __sk_buff, sk). Por lo tanto, se permite y posteriormente procede a bpf_convert_ctx_access. Tenga en cuenta que para el caso \\\"is_narrower_load\\\" en convert_ctx_accesses(), insn-\u0026gt;off est\u00e1 alineado, por lo que cnt puede no ser 0 porque coincide con offsetof(struct __sk_buff, sk) en bpf_convert_ctx_access. Sin embargo, el tama\u00f1o objetivo permanece en 0 y el verificador genera una advertencia del kernel: error del verificador: error durante la conversi\u00f3n de acceso a ctx(1). Este parche corrige este error para devolver un error correcto de \\\"acceso a bpf_context no v\u00e1lido off=X size=Y\\\" en la instrucci\u00f3n de carga. El mismo problema afecta a varios campos en las estructuras de contexto que permiten acceso restringido. Algunos campos no afectados (para sk_msg, sk_lookup y sockopt) tambi\u00e9n se modificaron para usar bpf_ctx_range_ptr por consistencia. Tenga en cuenta que este fallo de syzkaller se report\u00f3 en el enlace \\\"Cierres\\\" a continuaci\u00f3n, que sol\u00eda referirse a un error diferente, corregido en el commit fce7bd8e385a (\\\"bpf/verifier: Handle BPF_LOAD_ACQ instructions in insn_def_regno()\\\"). Debido a que syzbot confundi\u00f3 de alguna manera los dos errores, el nuevo fallo y la reproducci\u00f3n no se reportaron a la lista de correo.\"}],\"metrics\":{},\"references\":[{\"url\":\"https://git.kernel.org/stable/c/202900ceeef67458c964c2af6e1427c8e533ea7c\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/e09299225d5ba3916c91ef70565f7d2187e4cca0\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"}]}}"
  }
}


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