CVE-2026-98012 PUBLISHED

net/sched: sfq: clamp quantum in change path

Assigner: Linux
Reserved: 25.09.2026 Published: 25.09.2026 Updated: 25.09.2026

In the Linux kernel, the following vulnerability has been resolved:

net/sched: sfq: clamp quantum in change path

sfq_change() accepts any non-negative quantum (only rejects (int)ctl->quantum < 0). With a crafted size table qdisc_pkt_len reaches ~2 GiB, so quantum=1 makes the deficit-refill loop spin ~2^31 times under the qdisc lock (a soft lockup / denial of service).

Add max(256U, ...) matching fq_codel_change(). Reject quantum > 1<<20 with -EINVAL, matching fq_codel_change() and the init clamp.

Conditions to recreate the bug: CONFIG_NET_SCH_SFQ=y. Requires CAP_NET_ADMIN (namespace-local via unshare -Urn suffices).

tc qdisc add dev dummy0 root sfq tc qdisc change dev dummy0 root sfq quantum 1 stab data 32768 size_log 15 cell_log 0

Product Status

Vendor Linux
Product Linux
Versions Default: unaffected
  • affected from 82bd38bd5467ece1ee274b493f51326cf5220a5a to f3820dce042a673fcb28cc31c87ee14257e21a17 (excl.)
  • affected from e4650d7ae4252f67e997a632adfae0dd74d3a99a to 534cd7ecbbc6e8a974f4003a5c1557439c6e0a72 (excl.)
  • affected from e4650d7ae4252f67e997a632adfae0dd74d3a99a to e6c1cb728e389354203a72bc77464c222a247aeb (excl.)
  • affected from e4650d7ae4252f67e997a632adfae0dd74d3a99a to fb9f88a33c516ea5c0bcd9a22ca288b246b34567 (excl.)
  • Version 843cacb88f42f426973f1ed11c6fb562558efb27 is affected
  • Version 4919649699c5f4dbae08b8e2ed536fc9d6c3c2aa is affected
  • Version 548cf048b426729a7a1fa6acd1271c010c9a7380 is affected
  • Version c49ac48fac51a6a54efd5963954d02bacf075085 is affected
  • Version 58ae7465f0e7113d45aa88a66bf2d203c71c195e is affected
  • affected from 6.12.13 to 6.12.111 (excl.)
  • affected from 5.4.297 to 5.5 (excl.)
  • affected from 5.10.239 to 5.11 (excl.)
  • affected from 5.15.186 to 5.16 (excl.)
  • affected from 6.1.129 to 6.2 (excl.)
  • affected from 6.6.76 to 6.7 (excl.)
Vendor Linux
Product Linux
Versions Default: affected
  • Version 6.13 is affected
  • unaffected from 0 to 6.13 (excl.)
  • unaffected from 6.12.111 to 6.12.* (incl.)
  • unaffected from 6.18.53 to 6.18.* (incl.)
  • unaffected from 7.2.7 to 7.2.* (incl.)
  • unaffected from 7.3-rc3 to * (incl.)

References