{
  "schema_version": "1.6.1",
  "id": "RPI-CVE-2026-64456",
  "modified": "2026-10-09T11:39:44Z",
  "upstream": [
    "CVE-2026-64456"
  ],
  "published": "2026-07-25T08:51:45Z",
  "summary": "hwrng: virtio: clamp device-reported used.len at copy_data()",
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nhwrng: virtio: clamp device-reported used.len at copy_data()\n\nrandom_recv_done() stores the device-reported used.len directly into\nvi->data_avail.  copy_data() then indexes vi->data[] using\nvi->data_idx (advanced by previous copy_data() calls) and issues a\nmemcpy() without re-validating either value against the posted\nbuffer size sizeof(vi->data) (SMP_CACHE_BYTES bytes, typically 32\nor 64).\n\nA malicious or buggy virtio-rng backend can set used.len beyond\nsizeof(vi->data), steering the memcpy() past the end of the inline\narray into adjacent kmalloc-1k slab bytes.  hwrng_fillfn() mixes\nthose bytes into the guest RNG, and guest root can also observe\nthem directly via /dev/hwrng.\n\nConcrete impact is inside the guest:\n\n - Memory-safety / hardening: any virtio-rng backend that\n   over-reports used.len causes the driver to read past vi->data\n   into unrelated slab contents.  hwrng_fillfn() is a kernel thread\n   that runs as soon as the device is probed; no guest userspace\n   interaction is required to first-trigger the OOB.\n\n - Cross-boundary leak (confidential-compute threat model): a\n   malicious hypervisor cooperating with a malicious or compromised\n   guest root userspace can use /dev/hwrng as a leak channel for\n   guest-kernel heap data.  The host sets a large used.len, guest\n   root reads /dev/hwrng, and the returned bytes contain guest\n   kernel slab contents that were adjacent to vi->data.  In\n   practice, confidential-compute guests (SEV-SNP, TDX) usually\n   disable virtio-rng entirely, so this path is narrow, but the\n   fix is still worth carrying because the underlying\n   memory-safety bug contaminates the guest RNG on any host.\n\nKASAN confirms the OOB on a 7.1-rc4 guest whose virtio-rng backend\nhas been patched to report used.len = 0x10000:\n\n  BUG: KASAN: slab-out-of-bounds in virtio_read+0x394/0x5d0\n  Read of size 64 at addr ffff88800ae0ba20 by task hwrng/52\n  Call Trace:\n   __asan_memcpy+0x23/0x60\n   virtio_read+0x394/0x5d0\n   hwrng_fillfn+0xb2/0x470\n   kthread+0x2cc/0x3a0\n  Allocated by task 1:\n   probe_common+0xa5/0x660\n   virtio_dev_probe+0x549/0xbc0\n  The buggy address belongs to the object at ffff88800ae0b800\n   which belongs to the cache kmalloc-1k of size 1024\n  The buggy address is located 0 bytes to the right of\n   allocated 544-byte region [ffff88800ae0b800, ffff88800ae0ba20)\n\nSame class of bug as commit c04db81cd028 (\"net/9p: Fix buffer\noverflow in USB transport layer\"), which hardened\nusb9pfs_rx_complete() against unchecked device-reported length in\nthe USB 9p transport.\n\nWith the clamp at point of use and array_index_nospec() in place,\nthe same harness boots cleanly: copy_data() returns zero for the\nbogus report, the device-supplied bytes after data_idx are\ndiscarded, and the driver issues a fresh request.",
  "severity": [
    {
      "type": "CVSS_V3",
      "score": "CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H"
    }
  ],
  "affected": [
    {
      "package": {
        "ecosystem": "Raspberry Pi OS:12",
        "name": "linux"
      },
      "versions": [
        "1:6.1.47-1+rpt4"
      ],
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "linux-image-6.1.0-rpi3-rpi-2712",
            "binary_version": "1:6.1.47-1+rpt4"
          },
          {
            "binary_name": "linux-image-6.1.0-rpi3-rpi-v6",
            "binary_version": "1:6.1.47-1+rpt4"
          },
          {
            "binary_name": "linux-image-6.1.0-rpi3-rpi-v7",
            "binary_version": "1:6.1.47-1+rpt4"
          },
          {
            "binary_name": "linux-image-6.1.0-rpi3-rpi-v7l",
            "binary_version": "1:6.1.47-1+rpt4"
          },
          {
            "binary_name": "linux-image-6.1.0-rpi3-rpi-v8",
            "binary_version": "1:6.1.47-1+rpt4"
          }
        ]
      },
      "database_specific": {
        "per_version": {
          "1:6.1.47-1+rpt4": {
            "linux_commit": "655fc658a15ae7a6f37103754adb39ba52a9a14e",
            "upstream_version": "6.1.47",
            "assessment": "commit ancestry (strak rule)",
            "upstream_fixed": "6.1.178",
            "compiled_filter": false
          }
        }
      }
    }
  ],
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://www.cve.org/CVERecord?id=CVE-2026-64456"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/3aa3e89cf80721c8d382b4c1a2b70a0449dad4a5"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/63335e7b638ae70028ae285bb95153874a8bc852"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/2e788948ff2a13358a303af112497a63201c5739"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/fde19b0d4eeabae042519313c843fe6f27d41e9d"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/81dd21b5f0c299cc7b5bf84f04a61938559d20e6"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/285e17c44e3873a73460f294acbd64018ff64385"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/92d5736a62040ec1cfff23ea57e6599301690ad5"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/e3046eeada299f917a8ad883af4434bfb86556b1"
    }
  ],
  "database_specific": {
    "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git",
    "upstream_modified": "2026-08-17T05:24:08Z",
    "severity": {
      "source": "kernel CNA",
      "cvss_v3_score": 7.7,
      "cvss_v3_severity": "High",
      "scenario": "AV:L - The attacker must control a virtio-rng backend or hypervisor locally attached to the guest; no network or physical packet path reaches this driver.\nAC:L - The backend directly controls the 32-bit used.len and can deterministically over-report it without winning a race or manipulating an uncertain memory layout.\nPR:N - No privileges inside the vulnerable guest are required because the hwrng kernel thread automatically consumes backend completions after device registration.\nUI:N - The automatically started hwrng thread triggers the out-of-bounds read without any victim action or guest userspace request.\nS:U - The vulnerable driver and the affected memory, RNG state, and availability all belong to the same guest-kernel security authority; this is not a guest-to-host escape.\nC:H - Repeated bounded copies advance through a device-selected, potentially enormous length, producing sequential out-of-bounds reads of guest-kernel heap memory that guest root can observe through /dev/hwrng.\nI:N - The memcpy destination remains bounded by the hwrng core buffer, so the flaw provides no out-of-bounds write, use-after-free, or control-flow modification primitive.\nA:H - A sufficiently large reported length drives reads beyond valid slab memory, causing a kernel out-of-bounds fault, oops, or panic, and the malicious backend can trigger it repeatedly."
    }
  }
}