CVE-2026-22976: In 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---