CVE-2026-98547 (GCVE-0-2026-98547)
Vulnerability from cvelistv5
Published
2026-10-18 15:18
Modified
2026-10-19 09:21
Severity ?
Summary
In the Linux kernel, the following vulnerability has been resolved: af_packet: fix integer overflow in prb_calc_retire_blk_tmo() prb_calc_retire_blk_tmo() computes in 32-bit int arithmetic: mbits = (blk_size_in_bytes * 8) / (1024 * 1024); If I'm reading the validation right, tp_block_size is user controlled and packet_set_ring() only rejects values that are <= 0 as int or not page aligned, so a 256MiB block goes right through (and alloc_one_pg_vec_page() even has a vzalloc fallback for it). 0x10000000 * 8 wraps to INT_MIN, and on a NIC reporting 1 Gbps (div == 1) the function ends up returning -2047. The condition is actually (8 * size) mod 2^32 >= 2^31 && div == 1, so the trigger set is [256,512), [768,1024), [1280,1536) and [1792,2048) MiB. Other sizes wrap to non-negative values and faster links divide the unsigned value back below 2^31, which is why this doesn't blow up for everyone. What makes it fatal is what happens next in init_prb_bdqc(): p1->interval_ktime = ms_to_ktime(prb_calc_retire_blk_tmo(...)); hrtimer_start(&p1->retire_blk_timer, p1->interval_ktime, HRTIMER_MODE_REL_SOFT); A negative relative timeout expires immediately. The callback unconditionally returns HRTIMER_RESTART, and hrtimer_forward() turns the negative interval into hrtimer_resolution: if (interval < hrtimer_resolution) interval = hrtimer_resolution; So the SOFT timer re-fires at the maximum rate forever, holding sk_receive_queue.lock each pass. One CPU spins in softirq until the socket is closed. Repeat with more rings and the machine is gone. The overflow itself is ancient - it was introduced together with TPACKET_V3 in f6fb8f100b80 ("af-packet: TPACKET_V3 flexible buffer implementation."). Its effect prior to f7460d2989fa ("net: af_packet: Use hrtimer to do the retire operation", v6.18) was not as clear-cut, though: the return value was stored into an unsigned short retire_blk_tov, so a negative result was truncated, and a 0-jiffy delay loop could be programmed as well. Neither is nearly as detrimental as the immediate maximum-rate spin the hrtimer conversion turned it into. (Unrelated to CVE-2019-20812 - that one was the ethtool failure path returning 0, which now returns DEFAULT_PRB_RETIRE_TOV.) Reproducer, needs CAP_NET_RAW (a --network host container has it by default) and a 1 Gbps NIC (QEMU e1000 works): int fd = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_ALL)); bind(fd, ...); int v = TPACKET_V3; setsockopt(fd, SOL_PACKET, PACKET_VERSION, &v, sizeof(v)); struct tpacket_req3 req = { .tp_block_size = 0x10000000, .tp_block_nr = 1, .tp_frame_size = 2048, .tp_frame_nr = 0x10000000 / 2048, .tp_retire_blk_tov = 0, }; setsockopt(fd, SOL_PACKET, PACKET_RX_RING, &req, sizeof(req)); Compute in 64 bits instead. The operands are already bounded by the existing validation, so nothing else changes. If you'd prefer a different fix, just say so and I'll respin.
References
Impacted products
Vendor Product Version
Linux Linux Version: f6fb8f100b807378fda19e83e5ac6828b638603a
Version: f6fb8f100b807378fda19e83e5ac6828b638603a
Version: f6fb8f100b807378fda19e83e5ac6828b638603a
Version: f6fb8f100b807378fda19e83e5ac6828b638603a
Version: f6fb8f100b807378fda19e83e5ac6828b638603a
Version: f6fb8f100b807378fda19e83e5ac6828b638603a
Version: f6fb8f100b807378fda19e83e5ac6828b638603a
Version: f6fb8f100b807378fda19e83e5ac6828b638603a
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{
  "containers": {
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        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/packet/af_packet.c"
          ],
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              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
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              "negate": false,
              "operator": "OR"
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      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\naf_packet: fix integer overflow in prb_calc_retire_blk_tmo()\n\nprb_calc_retire_blk_tmo() computes in 32-bit int arithmetic:\n\n        mbits = (blk_size_in_bytes * 8) / (1024 * 1024);\n\nIf I\u0027m reading the validation right, tp_block_size is user\ncontrolled and packet_set_ring() only rejects values that are \u003c= 0\nas int or not page aligned, so a 256MiB block goes right through\n(and alloc_one_pg_vec_page() even has a vzalloc fallback for it).\n0x10000000 * 8 wraps to INT_MIN, and on a NIC reporting 1 Gbps\n(div == 1) the function ends up returning -2047.\n\nThe condition is actually (8 * size) mod 2^32 \u003e= 2^31 \u0026\u0026 div == 1,\nso the trigger set is [256,512), [768,1024), [1280,1536) and\n[1792,2048) MiB. Other sizes wrap to non-negative values and faster\nlinks divide the unsigned value back below 2^31, which is why this\ndoesn\u0027t blow up for everyone.\n\nWhat makes it fatal is what happens next in init_prb_bdqc():\n\n        p1-\u003einterval_ktime = ms_to_ktime(prb_calc_retire_blk_tmo(...));\n        hrtimer_start(\u0026p1-\u003eretire_blk_timer, p1-\u003einterval_ktime,\n                      HRTIMER_MODE_REL_SOFT);\n\nA negative relative timeout expires immediately. The callback\nunconditionally returns HRTIMER_RESTART, and hrtimer_forward() turns\nthe negative interval into hrtimer_resolution:\n\n        if (interval \u003c hrtimer_resolution)\n                interval = hrtimer_resolution;\n\nSo the SOFT timer re-fires at the maximum rate forever, holding\nsk_receive_queue.lock each pass. One CPU spins in softirq until the\nsocket is closed. Repeat with more rings and the machine is gone.\n\nThe overflow itself is ancient - it was introduced together with\nTPACKET_V3 in f6fb8f100b80 (\"af-packet: TPACKET_V3 flexible buffer\nimplementation.\"). Its effect prior to f7460d2989fa (\"net:\naf_packet: Use hrtimer to do the retire operation\", v6.18) was not\nas clear-cut, though: the return value was stored into an unsigned\nshort retire_blk_tov, so a negative result was truncated, and a\n0-jiffy delay loop could be programmed as well. Neither is nearly\nas detrimental as the immediate maximum-rate spin the hrtimer\nconversion turned it into.\n\n(Unrelated to CVE-2019-20812 - that one was the ethtool failure path\nreturning 0, which now returns DEFAULT_PRB_RETIRE_TOV.)\n\nReproducer, needs CAP_NET_RAW (a --network host container has it by\ndefault) and a 1 Gbps NIC (QEMU e1000 works):\n\n        int fd = socket(AF_PACKET, SOCK_RAW, htons(ETH_P_ALL));\n        bind(fd, ...);\n        int v = TPACKET_V3;\n        setsockopt(fd, SOL_PACKET, PACKET_VERSION, \u0026v, sizeof(v));\n        struct tpacket_req3 req = {\n                .tp_block_size = 0x10000000,\n                .tp_block_nr = 1,\n                .tp_frame_size = 2048,\n                .tp_frame_nr = 0x10000000 / 2048,\n                .tp_retire_blk_tov = 0,\n        };\n        setsockopt(fd, SOL_PACKET, PACKET_RX_RING, \u0026req, sizeof(req));\n\nCompute in 64 bits instead. The operands are already bounded by the\nexisting validation, so nothing else changes. If you\u0027d prefer a\ndifferent fix, just say so and I\u0027ll respin."
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-19T09:21:30.417Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/02afd75649a4e001031ed82153a5c39312ec0737"
        },
        {
          "url": "https://git.kernel.org/stable/c/eb5b3838b9200dac04bfe33483db0ee8287456fb"
        },
        {
          "url": "https://git.kernel.org/stable/c/297acc571d5813db76b147c745b91031d5f9c960"
        },
        {
          "url": "https://git.kernel.org/stable/c/be1aacff399d519cc48d6b34354a54dd79041140"
        },
        {
          "url": "https://git.kernel.org/stable/c/b2bcc6a254d6f27823a56787668ae4ee8cdb6e71"
        },
        {
          "url": "https://git.kernel.org/stable/c/6279211e7d2456ecd195d236c9ee5e5c6fa5a17a"
        },
        {
          "url": "https://git.kernel.org/stable/c/218a944b9e035d4b47d59c69af6ca13319da15fb"
        },
        {
          "url": "https://git.kernel.org/stable/c/56d82862a0a243ac14ba11b6d7b57ddc2d064b95"
        }
      ],
      "title": "af_packet: fix integer overflow in prb_calc_retire_blk_tmo()",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-98547",
    "datePublished": "2026-10-18T15:18:15.669Z",
    "dateReserved": "2026-09-25T10:25:14.356Z",
    "dateUpdated": "2026-10-19T09:21:30.417Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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