{"cve":"CVE-2026-98547","nvd":{"published":"2026-10-18T16:17:06.630","modified":"2026-10-19T10:19:10.717","status":"Received","description":"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'm reading the validation right, tp_block_size is user\ncontrolled and packet_set_ring() only rejects values that are <= 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 >= 2^31 && 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't blow up for everyone.\n\nWhat makes it fatal is what happens next in init_prb_bdqc():\n\n        p1->interval_ktime = ms_to_ktime(prb_calc_retire_blk_tmo(...));\n        hrtimer_start(&p1->retire_blk_timer, p1->interval_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 < 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, &v, 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, &req, sizeof(req));\n\nCompute in 64 bits instead. The operands are already bounded by the\nexisting validation, so nothing else changes. If you'd prefer a\ndifferent fix, just say so and I'll respin.","cvss_v4":null,"cvss_v3":null,"cwes":[],"references":["https://git.kernel.org/stable/c/02afd75649a4e001031ed82153a5c39312ec0737","https://git.kernel.org/stable/c/218a944b9e035d4b47d59c69af6ca13319da15fb","https://git.kernel.org/stable/c/297acc571d5813db76b147c745b91031d5f9c960","https://git.kernel.org/stable/c/56d82862a0a243ac14ba11b6d7b57ddc2d064b95","https://git.kernel.org/stable/c/6279211e7d2456ecd195d236c9ee5e5c6fa5a17a"],"products":[],"source":"nvd","synced_at":"2026-10-19T23:00:53.604569364+00:00"},"epss":{"cve":"CVE-2026-98547","score":0.00216,"percentile":0.11945,"date":"2026-10-25"},"kev":null,"osv":[],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}