{"cve":"CVE-2026-98022","nvd":{"published":"2026-09-25T11:17:30.740","modified":"2026-10-19T10:17:56.067","status":"Received","description":"In the Linux kernel, the following vulnerability has been resolved:\n\nnet: cap tx_queue_len at S16_MAX to prevent oversized ring allocations\n\nSeveral subsystems allocate ring buffers sized by dev->tx_queue_len\nwith no upper bound. An unprivileged user (via unshare -Urn) can set a\nhuge tx_queue_len and exhaust global memory with ring allocations:\n\n- pfifo_fast: pfifo_fast_init() and pfifo_fast_change_tx_queue_len()\n  allocate 3 skb_array rings of tx_queue_len entries each.\n- tun: tun_queue_resize() and the queue-attach path resize ptr_rings\n  to tx_queue_len on the NETDEV_CHANGE_TX_QUEUE_LEN notifier.\n- tap (macvtap/ipvtap): tap_queue_resize() and tap_init() resize/init\n  ptr_rings to tx_queue_len on the same notifier.\n\nnetif_change_tx_queue_len() is the single entry point for IFLA_TXQLEN,\nsysfs, and the SIOCSIFTXQLEN ioctl. Cap new_len at S16_MAX (32767)\nthere so the oversized value is rejected at set time. This takes\neffect whether the device is up or down, before dev->tx_queue_len is\nwritten, before any notifier fires, and before any ring is allocated.\nThe \"> S16_MAX\" check also subsumes the previous unsigned-long\ntruncation test, and a negative ifr_qlen from the ioctl lands far\nabove the cap after conversion, so both old failure modes are covered\nby the one comparison.\n\ntx_queue_len is ambigious: both a per-ring sizing multiplier and a\ndefault queue-length/limit knob for consumers that allocate\nnothing at set time (pfifo/bfifo/gred/plug/sfb limits, htb\ndirect_qlen, qfq max_classes, teql). 32767 is chosen as the largest\nvalue NLA_POLICY_FULL_RANGE can express for the u32 IFLA_TXQLEN\npolicy in patch 2/3 while staying a legitimate queue length on\nhigh-BDP paths; the ring-memory trade-off of a shared knob is\ndisclosed below.\n\nConditions to recreate the bug:\n- CONFIG_NET_SCHED=y, CONFIG_VETH=y, CONFIG_USER_NS=y, CONFIG_NET_NS=y.\n- Unprivileged user in a fresh user+net namespace (unshare -Urn).\n- pfifo_fast: create veth pairs, set tx_queue_len to 500000, attach\n  mq+pfifo_fast. ~28 iterations OOMs a 2GB guest.\n- tun: create 50 tun devices with IFF_MULTI_QUEUE, set tx_queue_len to\n  500000, open 8 queues each. ~1.6GB of ptr_ring allocations OOMs a\n  512MB guest.\n- tap: same as tun with IFF_TAP. ~960MB OOMs a 512MB guest.\n- On the fixed kernel the oversized tx_queue_len is rejected with\n  -ERANGE at set time (all four paths: RTM_SETLINK, RTM_NEWLINK\n  create, sysfs, ioctl - the latter two via this check, the former\n  two via this check and the 2/3 parse policy respectively).","cvss_v4":null,"cvss_v3":null,"cwes":[],"references":["https://git.kernel.org/stable/c/081340cf70a789b94b4174af54a63ffd49677a4e","https://git.kernel.org/stable/c/24d02c909a1725ab9eceb92db7d02e4e841f17ca","https://git.kernel.org/stable/c/5e5591a0f33f7c11bf1d338dbb6c5072575de64c","https://git.kernel.org/stable/c/66ab4c59b74db7ab53a1c9083feaaede393a96a0","https://git.kernel.org/stable/c/81c0e02076989743a603806a5a4f44d2c40dc01f"],"products":[],"source":"nvd","synced_at":"2026-10-19T22:56:02.509636177+00:00"},"epss":{"cve":"CVE-2026-98022","score":0.00177,"percentile":0.07176,"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."]}