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CVE-2025-38591

Estado: ModificadaMedia (5.5)—

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:

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:

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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.

Detalles técnicos trazas, registros y código del informe original
    r0 = *(u8 *)(r1 + 169);
    exit;

    verifier bug: error during ctx access conversion(1)

CVSS

Probabilidad de explotación (EPSS)

EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).

Tecnologías afectadas (1)

Linux — Linux Kernel

CWE

Referencias

JSON original (NVD)

Mostrar
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      "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't 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->off\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't get reported to the mailing list."
    },
    {
      "lang": "es",
      "value": "En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: bpf: Rechazo de acceso más estrecho a campos de puntero ctx. El siguiente programa BPF, simplificado a partir de una reproducción 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 más 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->off está 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 tamaño objetivo permanece en 0 y el verificador genera una advertencia del kernel: error del verificador: error durante la conversión de acceso a ctx(1). Este parche corrige este error para devolver un error correcto de \"acceso a bpf_context no válido off=X size=Y\" en la instrucción 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) también se modificaron para usar bpf_ctx_range_ptr por consistencia. Tenga en cuenta que este fallo de syzkaller se reportó en el enlace \"Cierres\" a continuación, que solía 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 confundió de alguna manera los dos errores, el nuevo fallo y la reproducción no se reportaron a la lista de correo."
    }
  ],
  "lastModified": "2026-09-14T12:17:36.590",
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