CVE-2026-98234

Summary

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

net/sched: hhf: cap hh_flows_limit at change time

hhf_change() stores TCA_HHF_HH_FLOWS_LIMIT with no upper bound. A huge hh_flows_limit lets each new heavy-hitter flow pass the hh_flows_current_cnt check in alloc_new_hh() and forces a fixed-size kzalloc(GFP_ATOMIC) per flow under spoofed traffic, for unbounded memory growth.

Bound the attribute with NLA_POLICY_MAX() at 2*HH_FLOWS_CNT (the hhf_init() default) and report the rejected value via extack. The deprecated nested parse is kept: legacy tc does not set NLA_F_NESTED on TCA_OPTIONS. Configs relying on hh_limit above the default were relying on unbounded, unsafe behaviour and are not supported going forward.

hhf_init() also ran hhf_change() before setting the default hh_flows_limit, so a user-supplied hh_limit at add time was clobbered back to 2048. Set the default before hhf_change() so the configured value sticks.

This is a follow-up to commit eb56a495f59b ("net/sched: hhf: clamp quantum in change and init paths"), which bounded the quantum of the same qdisc; the hh_flows_limit bound is the remaining unbounded knob of that series' scope.

Conditions to recreate the bug: CAP_NET_ADMIN in a user namespace; tc qdisc change dev X root hhf hh_limit 4294967295 succeeds and the value is echoed by tc qdisc show, unbounding heavy-hitter flow allocations; also tc qdisc add dev X root hhf hh_limit 500 stores 2048 instead of 500.

Affected Software

VendorProductVersion RangeStatus
LinuxLinux10239edf86f137ce4c39b62ea9575e8053c549a0 < 7adfd0a42174b85c6bd678858ecd6674f403f336affected
LinuxLinux10239edf86f137ce4c39b62ea9575e8053c549a0 < 35fd423a5c5132c6f4321f6c4f0a7b4b90af830caffected
LinuxLinux10239edf86f137ce4c39b62ea9575e8053c549a0 < 06d2a101e89063cb0b9b459104db48bdfb0a797daffected
LinuxLinux10239edf86f137ce4c39b62ea9575e8053c549a0 < d8e2f1f0263b7c97b222c06070cccf13e0ab7112affected
LinuxLinux10239edf86f137ce4c39b62ea9575e8053c549a0 < f3f4a5cb4a6e9b1f1f25d34dfc25f836a1601db4affected
LinuxLinux10239edf86f137ce4c39b62ea9575e8053c549a0 < 1731ff1d20489afe4cd01b7d16d37f324746ac54affected
LinuxLinux10239edf86f137ce4c39b62ea9575e8053c549a0 < f6547d27ce2093c5627636fb63dd0b7523c466f9affected
LinuxLinux10239edf86f137ce4c39b62ea9575e8053c549a0 < 2cef2588c995722a901368def30befeef9ae55c6affected
LinuxLinux3.14affected
LinuxLinux0 < 3.14unaffected
LinuxLinux5.10.271 <= 5.10.*unaffected
LinuxLinux5.15.222 <= 5.15.*unaffected
LinuxLinux6.1.189 <= 6.1.*unaffected
LinuxLinux6.6.158 <= 6.6.*unaffected
LinuxLinux6.12.112 <= 6.12.*unaffected
LinuxLinux6.18.54 <= 6.18.*unaffected
LinuxLinux7.2.8 <= 7.2.*unaffected
LinuxLinux7.3-rc4 <= *unaffected

Weaknesses

References