CVE-2026-97958

net/sched: cls_api: Don't replay RTM_GETCHAIN in tc_ctl_chain().

Published Sep 25, 2026 CVSS 3.1 · 5.5 Medium EPSS < 1% KEV · Not listed
Description
In the Linux kernel, the following vulnerability has been resolved:

net/sched: cls_api: Don't replay RTM_GETCHAIN in tc_ctl_chain().

If a netlink socket sends RTM_GETCHAIN requests repeatedly
without recv()ing the responses, tc_ctl_chain() hogs CPU and
triggers Hung Task splat. [0]

As caught in the stack trace, netlink_attachskb() could confuse
tc_ctl_chain() by returning -EAGAIN when the userspace netlink
socket's receive buffer is full.

The replay: label exists since commit 32a4f5ecd738 ("net: sched:
introduce chain object to uapi") but was not used initially.

Since commit 9f407f1768d3 ("net: sched: introduce chain templates"),
the label is needed for RTM_NEWCHAIN because tcf_proto_lookup_ops()
may release RTNL to call request_module().

However, the replay logic is unnecessary for RTM_GETCHAIN.

Let's apply the replay logic only for RTM_NEWCHAIN.

[0]:
INFO: task repro:1018 is blocked on a mutex likely owned by task repro:1022.
task:repro state:R running task stack:14096 pid:1022 tgid:1014 ppid:961 task_flags:0x400040 flags:0x00080000
Call Trace:
<TASK>
? clockevents_program_event (kernel/time/clockevents.c:372)
? pskb_expand_head (net/core/skbuff.c:615)
? skb_release_data (net/core/skbuff.c:1122)
? netlink_attachskb (./include/linux/skbuff.h:1323 ./include/linux/skbuff.h:1332 net/netlink/af_netlink.c:1232)
? __netlink_lookup (./include/linux/rcupdate.h:882 ./include/linux/rhashtable.h:711 net/netlink/af_netlink.c:499)
? tc_chain_notify (net/sched/cls_api.c:3045)
? tc_chain_notify (./include/linux/skbuff.h:1384 net/sched/cls_api.c:3041)
? netlink_unicast (net/netlink/af_netlink.c:1335)
? rtnl_unicast (./include/net/netlink.h:1198 net/core/rtnetlink.c:985)
? tc_ctl_chain (net/sched/cls_api.c:3242)
? rtnetlink_rcv_msg (net/core/rtnetlink.c:7146)
? netlink_unicast (net/netlink/af_netlink.c:1354)
? __pfx_rtnetlink_rcv_msg (net/core/rtnetlink.c:7177)
? netlink_rcv_skb (net/netlink/af_netlink.c:2556)
? netlink_unicast (net/netlink/af_netlink.c:1319)
? netlink_sendmsg (net/netlink/af_netlink.c:1900)
? __sock_sendmsg (net/socket.c:800)
? __sys_sendto (net/socket.c:2281)
? __x64_sys_sendto (net/socket.c:2288 net/socket.c:2284 net/socket.c:2284)
? do_syscall_64 (arch/x86/entry/syscall_64.c:61 arch/x86/entry/syscall_64.c:84)
? entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121)
</TASK>

Remediation

No solution or workaround provided in the CVE record

Tracking

Sign in to view the affected projects.

Advisories

Source ID Title
Debian DLA Debian DLA DLA-4817-1 linux-6.12 security update
Debian DLA Debian DLA DLA-4841-1 linux security update
Debian DSA Debian DSA DSA-6528-1 linux security update
Ubuntu USN Ubuntu USN USN-8961-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-9019-1 Linux kernel (Azure) vulnerabilities
Ubuntu USN Ubuntu USN USN-9020-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-9022-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-9023-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-9024-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-9025-1 Linux kernel vulnerabilities
Ubuntu USN Ubuntu USN USN-9026-1 Linux kernel (Azure) vulnerabilities
Ubuntu USN Ubuntu USN USN-9029-1 Linux kernel (Raspberry Pi) vulnerabilities
Ubuntu USN Ubuntu USN USN-9039-1 Linux kernel (Azure CVM) vulnerabilities
Ubuntu USN Ubuntu USN USN-9040-1 Linux kernel (Low Latency NVIDIA) vulnerabilities
Ubuntu USN Ubuntu USN USN-9066-1 Linux kernel (HWE) vulnerabilities
Ubuntu USN Ubuntu USN USN-9091-1 Linux kernel (NVIDIA Tegra) vulnerabilities
History
Type Values Removed Values Added
Weaknesses CWE-400
Type Values Removed Values Added
Weaknesses CWE-835
References
Metrics threat_severity

None

cvssV3_1

{'score': 5.5, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H'}

threat_severity

Low

Type Values Removed Values Added
Weaknesses CWE-400
Type Values Removed Values Added
Description In the Linux kernel, the following vulnerability has been resolved: net/sched: cls_api: Don't replay RTM_GETCHAIN in tc_ctl_chain(). If a netlink socket sends RTM_GETCHAIN requests repeatedly without recv()ing the responses, tc_ctl_chain() hogs CPU and triggers Hung Task splat. [0] As caught in the stack trace, netlink_attachskb() could confuse tc_ctl_chain() by returning -EAGAIN when the userspace netlink socket's receive buffer is full. The replay: label exists since commit 32a4f5ecd738 ("net: sched: introduce chain object to uapi") but was not used initially. Since commit 9f407f1768d3 ("net: sched: introduce chain templates"), the label is needed for RTM_NEWCHAIN because tcf_proto_lookup_ops() may release RTNL to call request_module(). However, the replay logic is unnecessary for RTM_GETCHAIN. Let's apply the replay logic only for RTM_NEWCHAIN. [0]: INFO: task repro:1018 is blocked on a mutex likely owned by task repro:1022. task:repro state:R running task stack:14096 pid:1022 tgid:1014 ppid:961 task_flags:0x400040 flags:0x00080000 Call Trace: <TASK> ? clockevents_program_event (kernel/time/clockevents.c:372) ? pskb_expand_head (net/core/skbuff.c:615) ? skb_release_data (net/core/skbuff.c:1122) ? netlink_attachskb (./include/linux/skbuff.h:1323 ./include/linux/skbuff.h:1332 net/netlink/af_netlink.c:1232) ? __netlink_lookup (./include/linux/rcupdate.h:882 ./include/linux/rhashtable.h:711 net/netlink/af_netlink.c:499) ? tc_chain_notify (net/sched/cls_api.c:3045) ? tc_chain_notify (./include/linux/skbuff.h:1384 net/sched/cls_api.c:3041) ? netlink_unicast (net/netlink/af_netlink.c:1335) ? rtnl_unicast (./include/net/netlink.h:1198 net/core/rtnetlink.c:985) ? tc_ctl_chain (net/sched/cls_api.c:3242) ? rtnetlink_rcv_msg (net/core/rtnetlink.c:7146) ? netlink_unicast (net/netlink/af_netlink.c:1354) ? __pfx_rtnetlink_rcv_msg (net/core/rtnetlink.c:7177) ? netlink_rcv_skb (net/netlink/af_netlink.c:2556) ? netlink_unicast (net/netlink/af_netlink.c:1319) ? netlink_sendmsg (net/netlink/af_netlink.c:1900) ? __sock_sendmsg (net/socket.c:800) ? __sys_sendto (net/socket.c:2281) ? __x64_sys_sendto (net/socket.c:2288 net/socket.c:2284 net/socket.c:2284) ? do_syscall_64 (arch/x86/entry/syscall_64.c:61 arch/x86/entry/syscall_64.c:84) ? entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:121) </TASK>
Title net/sched: cls_api: Don't replay RTM_GETCHAIN in tc_ctl_chain().
First Time appeared Linux
Linux linux Kernel
CPEs cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
Vendors & Products Linux
Linux linux Kernel
References
Weaknesses

Sources

Status
PUBLISHED
Assigner
Linux
Published
Updated
Oct 19, 2026, 9:11 AM
Reserved
Sep 25, 2026, 10:18 AM
Status
Received
Published
Sep 25, 2026, 11:17 AM
Modified
Oct 19, 2026, 10:17 AM
Severity
Low
Public date
Sep 25, 2026, 12:00 AM