fkie_cve-2025-38591
Vulnerability from fkie_nvd
Published
2025-08-19 17:15
Modified
2025-08-20 14:40
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


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{
  "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."
    }
  ],
  "id": "CVE-2025-38591",
  "lastModified": "2025-08-20T14:40:17.713",
  "metrics": {},
  "published": "2025-08-19T17:15:36.790",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/202900ceeef67458c964c2af6e1427c8e533ea7c"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/e09299225d5ba3916c91ef70565f7d2187e4cca0"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Awaiting Analysis"
}


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