net/sched: sch_hfsc: bound the classify inner-filter walk with a drift budget

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Summary

CVECVE-2026-98610
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-10-18 16:17:13 UTC
Updated2026-10-19 10:19:23 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: net/sched: sch_hfsc: bound the classify inner-filter walk with a drift budget hfsc_classify() applies the "filter may only point downwards" level check only when the filter result carries no bound class. A filter created with a flowid gets res.class set once at bind time, so the check never runs for it during classification. hfsc_adjust_levels() can later raise a class's level without revalidating existing bindings, leaving two binds that were each legal at bind time pointing at each other; the classify walk then bounces between two interior classes forever with the qdisc lock held and BH disabled — a soft lockup from a single packet. The stuck walk trips the watchdog: watchdog: BUG: soft lockup - CPU#3 stuck for 13s! [ping:444] RIP: 0010:u32_classify+0x542/0x17f0 ... tcf_classify+0x66/0xa0 hfsc_enqueue+0x166/0xdf0 Bound the traversal with a budget of non-descending hops, the only way a configured walk can move without descending the class tree once levels drift after bind time. The budget is cumulative over the whole walk and is deliberately not reset on a descending hop: a chain that alternates a descent with a lateral hop would return the budget every lap and never trip. Descending hops never decrement it, so legitimately deep trees are unaffected and a terminating lateral chain still classifies normally. Drop the packet with a rate-limited warning once the budget is exhausted, mirroring the merged HTB fix. This is a follow-up to commit 729c4896ab82 ("net/sched: sch_htb: limit htb_classify inner-class filter hops"), which bounded the same classify loop on the HTB side but left the HFSC walk unbounded. Conditions to recreate the bug: - CONFIG_NET_SCHED, CONFIG_NET_SCH_HFSC, CONFIG_NET_CLS_U32, CONFIG_LOCKUP_DETECTOR. - Build a cycle with two legal-at-bind-time flowid binds and a level drift: class X 1:1 (child of root) with leaf child 1:10; class Y 1:2 (sibling of X) with children 1:20 and 1:200; root u32 filter flowid 1:1; filter on X flowid 1:2 (legal when Y is a leaf); after Y's level rises to 2, filter on Y flowid 1:1 (legal then). Send one packet (ping on the device). Unfixed kernel: classify spins with the qdisc lock held; with softlockup_panic=1 it panics. - Reachable from unprivileged user via unshare -Urn (CAP_NET_ADMIN).

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected a2f79227138c71e08627af5f8961197364edbc98 d4fd251e3311727c32af89344d3332f788c153a2 git Not specified
CNA Linux Linux affected a2f79227138c71e08627af5f8961197364edbc98 30d7fea767e830bd81ac2f73d2e33c877cb2e679 git Not specified
CNA Linux Linux affected a2f79227138c71e08627af5f8961197364edbc98 f476fb656ca2326d7b2eba98d03ced1cbcf5cd99 git Not specified
CNA Linux Linux affected a2f79227138c71e08627af5f8961197364edbc98 e8f9979286f70dfbfe0552e2a63000950841bea6 git Not specified
CNA Linux Linux affected a2f79227138c71e08627af5f8961197364edbc98 2bd20245dd658789d8cccb37697967b4caba6ad8 git Not specified
CNA Linux Linux affected a2f79227138c71e08627af5f8961197364edbc98 0fa25ba50a382d79c0cf060214c2095756836f5f git Not specified
CNA Linux Linux affected a2f79227138c71e08627af5f8961197364edbc98 1301a1292c6742b4c96a18715d49f89c3caca0d7 git Not specified
CNA Linux Linux affected a2f79227138c71e08627af5f8961197364edbc98 8a60ade2277e1f0e0d0578d565354e52292fa46d git Not specified
CNA Linux Linux affected 2.6.35 Not specified
CNA Linux Linux unaffected 2.6.35 semver Not specified
CNA Linux Linux unaffected 5.10.271 5.10.* semver Not specified
CNA Linux Linux unaffected 5.15.222 5.15.* semver Not specified
CNA Linux Linux unaffected 6.1.189 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.158 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.112 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.55 6.18.* semver Not specified
CNA Linux Linux unaffected 7.2.9 7.2.* semver Not specified
CNA Linux Linux unaffected 7.3 * original_commit_for_fix Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/d4fd251e3311727c32af89344d3332f788c153a2 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/30d7fea767e830bd81ac2f73d2e33c877cb2e679 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/0fa25ba50a382d79c0cf060214c2095756836f5f 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/2bd20245dd658789d8cccb37697967b4caba6ad8 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/1301a1292c6742b4c96a18715d49f89c3caca0d7 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/f476fb656ca2326d7b2eba98d03ced1cbcf5cd99 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/8a60ade2277e1f0e0d0578d565354e52292fa46d 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
git.kernel.org/stable/c/e8f9979286f70dfbfe0552e2a63000950841bea6 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org
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