CVE-2026-80630

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

net/sched: schfqcodel: Do not call qdisctreereduce_backlog during peek before restoring qlen

Whenever fq_codel drops packets during peek, it calls

qdisctreereduce_backlog. An issue arises because it calls

qdisctreereduce_backlog before it reincrements the qlen. If qlen drops

to zero, but peek returns an skb, the parent's qlen_notify callback will be

executed even though fq_codel still has 1 packet on the queue and, thus,

will mistakenly deactivate the parent's class causing issues like a recent

report [1] and a wild memory access in qfq:

[   29.371146][  T360] Oops: general protection fault, probably for non-canonical address 0xfbd59c0000000024: 0000 [#1] SMP KASAN NOPTI

[   29.371666][  T360] KASAN: maybe wild-memory-access in range [0xdead000000000120-0xdead000000000127]

[   29.371987][  T360] CPU: 6 UID: 0 PID: 360 Comm: tc Not tainted 7.1.0-rc5-00285-gc530e5b2dbc6-dirty #82 PREEMPT(full)

[   29.372384][  T360] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011

[   29.372620][  T360] RIP: 0010:qfqdeactivateagg (include/linux/list.h:1029 (discriminator 2) include/linux/list.h:1043 (discriminator 2) net/sched/schqfq.c:1369 (discriminator 2) net/sched/schqfq.c:1395 (discriminator 2)) sch_qfq

[   29.373544][  T360] RSP: 0018:ffff888102417370 EFLAGS: 00010216

[   29.373800][  T360] RAX: 0000000000000000 RBX: ffff88811224d568 RCX: dffffc0000000000

[   29.374079][  T360] RDX: 1ffff11021fe1543 RSI: ffff88810ff0aa00 RDI: dffffc0000000000

[   29.374368][  T360] RBP: ffff88811224c280 R08: dead000000000122 R09: 1bd5a00000000024

[   29.374649][  T360] R10: fffffbfff7940329 R11: fffffbfff7940329 R12: 0000000000000000

[   29.374926][  T360] R13: dead000000000100 R14: ffff88811224d580 R15: ffff88811224d578

[   29.375207][  T360] FS:  00007f5b794e5780(0000) GS:ffff88815d1e9000(0000) knlGS:0000000000000000

[   29.375545][  T360] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033

[   29.375823][  T360] CR2: 000055ffb091f000 CR3: 000000010a305000 CR4: 0000000000750ef0

[   29.376103][  T360] PKRU: 55555554

[   29.376258][  T360] Call Trace:

[   29.376401][  T360]  <TASK>

...

[   29.376885][  T360] qfqresetqdisc (net/sched/schqfq.c:357 net/sched/schqfq.c:1487) sch_qfq

[   29.377074][  T360]  qdiscreset (net/sched/schgeneric.c:1057)

[   29.377414][  T360]  _qdiscdestroy (net/sched/sch_generic.c:1096)

[   29.377600][  T360]  qdiscgraft (net/sched/schapi.c:1062 net/sched/schapi.c:1053 net/sched/schapi.c:1159)

[   29.378593][  T360]  tcgetqdisc (net/sched/schapi.c:1528 net/sched/schapi.c:1556)

Fix this by only calling qdisctreereduce_backlog in peek after the

qlen is restored.

[1] http://lore.kernel.org/netdev/CAN2cbVe79oj0O9==m4+4x3v+O+qzRagA=2=wkrp9i9=CqYvyZA@mail.gmail.com/