net/sched: sch_qfq: Fix NULL deref when deactivating inactive aggregate in qfq_reset

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Summary

CVECVE-2026-22976
StatePUBLISHED
AssignerLinux
Source PriorityCVE Program / NVD first with legacy fallback
Published2026-01-21 07:16:01 UTC
Updated2026-06-02 14:16:45 UTC
DescriptionIn the Linux kernel, the following vulnerability has been resolved: net/sched: sch_qfq: Fix NULL deref when deactivating inactive aggregate in qfq_reset `qfq_class->leaf_qdisc->q.qlen > 0` does not imply that the class itself is active. Two qfq_class objects may point to the same leaf_qdisc. This happens when: 1. one QFQ qdisc is attached to the dev as the root qdisc, and 2. another QFQ qdisc is temporarily referenced (e.g., via qdisc_get() / qdisc_put()) and is pending to be destroyed, as in function tc_new_tfilter. When packets are enqueued through the root QFQ qdisc, the shared leaf_qdisc->q.qlen increases. At the same time, the second QFQ qdisc triggers qdisc_put and qdisc_destroy: the qdisc enters qfq_reset() with its own q->q.qlen == 0, but its class's leaf qdisc->q.qlen > 0. Therefore, the qfq_reset would wrongly deactivate an inactive aggregate and trigger a null-deref in qfq_deactivate_agg: [ 0.903172] BUG: kernel NULL pointer dereference, address: 0000000000000000 [ 0.903571] #PF: supervisor write access in kernel mode [ 0.903860] #PF: error_code(0x0002) - not-present page [ 0.904177] PGD 10299b067 P4D 10299b067 PUD 10299c067 PMD 0 [ 0.904502] Oops: Oops: 0002 [#1] SMP NOPTI [ 0.904737] CPU: 0 UID: 0 PID: 135 Comm: exploit Not tainted 6.19.0-rc3+ #2 NONE [ 0.905157] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.17.0-0-gb52ca86e094d-prebuilt.qemu.org 04/01/2014 [ 0.905754] RIP: 0010:qfq_deactivate_agg (include/linux/list.h:992 (discriminator 2) include/linux/list.h:1006 (discriminator 2) net/sched/sch_qfq.c:1367 (discriminator 2) net/sched/sch_qfq.c:1393 (discriminator 2)) [ 0.906046] Code: 0f 84 4d 01 00 00 48 89 70 18 8b 4b 10 48 c7 c2 ff ff ff ff 48 8b 78 08 48 d3 e2 48 21 f2 48 2b 13 48 8b 30 48 d3 ea 8b 4b 18 0 Code starting with the faulting instruction =========================================== 0: 0f 84 4d 01 00 00 je 0x153 6: 48 89 70 18 mov %rsi,0x18(%rax) a: 8b 4b 10 mov 0x10(%rbx),%ecx d: 48 c7 c2 ff ff ff ff mov $0xffffffffffffffff,%rdx 14: 48 8b 78 08 mov 0x8(%rax),%rdi 18: 48 d3 e2 shl %cl,%rdx 1b: 48 21 f2 and %rsi,%rdx 1e: 48 2b 13 sub (%rbx),%rdx 21: 48 8b 30 mov (%rax),%rsi 24: 48 d3 ea shr %cl,%rdx 27: 8b 4b 18 mov 0x18(%rbx),%ecx ... [ 0.907095] RSP: 0018:ffffc900004a39a0 EFLAGS: 00010246 [ 0.907368] RAX: ffff8881043a0880 RBX: ffff888102953340 RCX: 0000000000000000 [ 0.907723] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000 [ 0.908100] RBP: ffff888102952180 R08: 0000000000000000 R09: 0000000000000000 [ 0.908451] R10: ffff8881043a0000 R11: 0000000000000000 R12: ffff888102952000 [ 0.908804] R13: ffff888102952180 R14: ffff8881043a0ad8 R15: ffff8881043a0880 [ 0.909179] FS: 000000002a1a0380(0000) GS:ffff888196d8d000(0000) knlGS:0000000000000000 [ 0.909572] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 [ 0.909857] CR2: 0000000000000000 CR3: 0000000102993002 CR4: 0000000000772ef0 [ 0.910247] PKRU: 55555554 [ 0.910391] Call Trace: [ 0.910527] <TASK> [ 0.910638] qfq_reset_qdisc (net/sched/sch_qfq.c:357 net/sched/sch_qfq.c:1485) [ 0.910826] qdisc_reset (include/linux/skbuff.h:2195 include/linux/skbuff.h:2501 include/linux/skbuff.h:3424 include/linux/skbuff.h:3430 net/sched/sch_generic.c:1036) [ 0.911040] __qdisc_destroy (net/sched/sch_generic.c:1076) [ 0.911236] tc_new_tfilter (net/sched/cls_api.c:2447) [ 0.911447] rtnetlink_rcv_msg (net/core/rtnetlink.c:6958) [ 0.911663] ? __pfx_rtnetlink_rcv_msg (net/core/rtnetlink.c:6861) [ 0.911894] netlink_rcv_skb (net/netlink/af_netlink.c:2550) [ 0.912100] netlink_unicast (net/netlink/af_netlink.c:1319 net/netlink/af_netlink.c:1344) [ 0.912296] ? __alloc_skb (net/core/skbuff.c:706) [ 0.912484] netlink_sendmsg (net/netlink/af ---truncated---

Risk And Classification

Primary CVSS: v3.1 5.5 MEDIUM from [email protected]

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Problem Types: CWE-476

CVSS v3.1 Breakdown

Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

NVD Known Affected Configurations (CPE 2.3)

TypeVendorProductVersionUpdateEditionLanguage
Operating System Linux Linux Kernel All All All All

Vendor Declared Affected Products

SourceVendorProductVersionPlatforms
CNA Linux Linux affected 0545a3037773512d3448557ba048cebb73b3e4af 6116a83ec167d3ab1390cded854d237481f41b63 git Not specified
CNA Linux Linux affected 0545a3037773512d3448557ba048cebb73b3e4af 0809c4bc06c9c961222df29f2eccfd449304056f git Not specified
CNA Linux Linux affected 0545a3037773512d3448557ba048cebb73b3e4af cdb24200b043438a144df501f1ebbd926bb1a2c7 git Not specified
CNA Linux Linux affected 0545a3037773512d3448557ba048cebb73b3e4af 11bf9134613f6c71fc0ff36c5d8d33856f6ae3bb git Not specified
CNA Linux Linux affected 0545a3037773512d3448557ba048cebb73b3e4af 43497313d0da3e12b5cfcd97aa17bf48ee663f95 git Not specified
CNA Linux Linux affected 0545a3037773512d3448557ba048cebb73b3e4af 51ffd447bc37bf1a5776b85523f51d2bc69977f6 git Not specified
CNA Linux Linux affected 0545a3037773512d3448557ba048cebb73b3e4af c1d73b1480235731e35c81df70b08f4714a7d095 git Not specified
CNA Linux Linux affected 3.0 Not specified
CNA Linux Linux unaffected 3.0 semver Not specified
CNA Linux Linux unaffected 5.10.248 5.10.* semver Not specified
CNA Linux Linux unaffected 5.15.198 5.15.* semver Not specified
CNA Linux Linux unaffected 6.1.161 6.1.* semver Not specified
CNA Linux Linux unaffected 6.6.121 6.6.* semver Not specified
CNA Linux Linux unaffected 6.12.66 6.12.* semver Not specified
CNA Linux Linux unaffected 6.18.6 6.18.* semver Not specified
CNA Linux Linux unaffected 6.19 * original_commit_for_fix Not specified
ADP Siemens RUGGEDCOM RST2428P affected V4.0 custom Not specified

References

ReferenceSourceLinkTags
git.kernel.org/stable/c/43497313d0da3e12b5cfcd97aa17bf48ee663f95 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/c1d73b1480235731e35c81df70b08f4714a7d095 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/11bf9134613f6c71fc0ff36c5d8d33856f6ae3bb 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/51ffd447bc37bf1a5776b85523f51d2bc69977f6 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
cert-portal.siemens.com/productcert/html/ssa-253495.html 0b142b55-0307-4c5a-b3c9-f314f3fb7c5e cert-portal.siemens.com
git.kernel.org/stable/c/6116a83ec167d3ab1390cded854d237481f41b63 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/0809c4bc06c9c961222df29f2eccfd449304056f 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
git.kernel.org/stable/c/cdb24200b043438a144df501f1ebbd926bb1a2c7 416baaa9-dc9f-4396-8d5f-8c081fb06d67 git.kernel.org Patch
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