[syzbot] [net?] KASAN: slab-use-after-free Read in qfq_reset_qdisc (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 143937ca51cc arm64, mm: avoid always making PTE dirty in p..
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
console output: https://syzkaller.appspot.com/x/log.txt?x=15939b04580000
kernel config: https://syzkaller.appspot.com/x/.config?x=158bd6857eb7a550
dashboard link: https://syzkaller.appspot.com/bug?extid=ec7176504e5bcc33ca4e
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
userspace arch: arm64
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=11763734580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17b9e3e2580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/a6ff641e43d2/disk-143937ca.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/22d9e0afd13f/vmlinux-143937ca.xz
kernel image: https://storage.googleapis.com/syzbot-assets/3ab2dee8c9ca/Image-143937ca.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ec7176...@syzkaller.appspotmail.com

do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
el0_svc+0x5c/0x254 arch/arm64/kernel/entry-common.c:746
el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:765
el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596
==================================================================
BUG: KASAN: slab-use-after-free in qfq_reset_qdisc+0xcc/0x208 net/sched/sch_qfq.c:1484
Read of size 8 at addr ffff0000ca2bfe50 by task syz.0.17/6716

CPU: 0 UID: 0 PID: 6716 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/30/2025
Call trace:
show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:499 (C)
__dump_stack+0x30/0x40 lib/dump_stack.c:94
dump_stack_lvl+0xd8/0x12c lib/dump_stack.c:120
print_address_description+0xa8/0x238 mm/kasan/report.c:378
print_report+0x68/0x84 mm/kasan/report.c:482
kasan_report+0xb0/0x110 mm/kasan/report.c:595
__asan_report_load8_noabort+0x20/0x2c mm/kasan/report_generic.c:381
qfq_reset_qdisc+0xcc/0x208 net/sched/sch_qfq.c:1484
qdisc_reset+0x128/0x598 net/sched/sch_generic.c:1038
__qdisc_destroy+0x134/0x4bc net/sched/sch_generic.c:1077
qdisc_put net/sched/sch_generic.c:1109 [inline]
dev_shutdown+0x35c/0x47c net/sched/sch_generic.c:1497
unregister_netdevice_many_notify+0xbb8/0x1de0 net/core/dev.c:12242
unregister_netdevice_many net/core/dev.c:12317 [inline]
unregister_netdevice_queue+0x2b4/0x300 net/core/dev.c:12161
unregister_netdevice include/linux/netdevice.h:3389 [inline]
__tun_detach+0x5d4/0x1304 drivers/net/tun.c:621
tun_detach drivers/net/tun.c:637 [inline]
tun_chr_close+0x118/0x1f8 drivers/net/tun.c:3436
__fput+0x340/0x75c fs/file_table.c:468
____fput+0x20/0x58 fs/file_table.c:496
task_work_run+0x1dc/0x260 kernel/task_work.c:227
resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
exit_to_user_mode_loop+0xfc/0x178 kernel/entry/common.c:43
exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
arm64_exit_to_user_mode arch/arm64/kernel/entry-common.c:103 [inline]
el0_svc+0x170/0x254 arch/arm64/kernel/entry-common.c:747
el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:765
el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596

Allocated by task 6716:
kasan_save_stack mm/kasan/common.c:56 [inline]
kasan_save_track+0x40/0x78 mm/kasan/common.c:77
kasan_save_alloc_info+0x44/0x54 mm/kasan/generic.c:573
poison_kmalloc_redzone mm/kasan/common.c:400 [inline]
__kasan_kmalloc+0x9c/0xb4 mm/kasan/common.c:417
kasan_kmalloc include/linux/kasan.h:262 [inline]
__kmalloc_cache_noprof+0x3a4/0x65c mm/slub.c:5748
kmalloc_noprof include/linux/slab.h:957 [inline]
kzalloc_noprof include/linux/slab.h:1094 [inline]
qfq_change_class+0x498/0xbe8 net/sched/sch_qfq.c:479
__tc_ctl_tclass net/sched/sch_api.c:2274 [inline]
tc_ctl_tclass+0x988/0x10b0 net/sched/sch_api.c:2304
rtnetlink_rcv_msg+0x624/0x97c net/core/rtnetlink.c:6963
netlink_rcv_skb+0x220/0x3fc net/netlink/af_netlink.c:2552
rtnetlink_rcv+0x28/0x38 net/core/rtnetlink.c:6981
netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
netlink_unicast+0x694/0x8c4 net/netlink/af_netlink.c:1346
netlink_sendmsg+0x648/0x930 net/netlink/af_netlink.c:1896
sock_sendmsg_nosec net/socket.c:727 [inline]
__sock_sendmsg net/socket.c:742 [inline]
____sys_sendmsg+0x490/0x7b8 net/socket.c:2630
___sys_sendmsg+0x204/0x278 net/socket.c:2684
__sys_sendmsg net/socket.c:2716 [inline]
__do_sys_sendmsg net/socket.c:2721 [inline]
__se_sys_sendmsg net/socket.c:2719 [inline]
__arm64_sys_sendmsg+0x184/0x238 net/socket.c:2719
__invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
invoke_syscall+0x98/0x254 arch/arm64/kernel/syscall.c:49
el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:132
do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
el0_svc+0x5c/0x254 arch/arm64/kernel/entry-common.c:746
el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:765
el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596

Freed by task 6716:
kasan_save_stack mm/kasan/common.c:56 [inline]
kasan_save_track+0x40/0x78 mm/kasan/common.c:77
__kasan_save_free_info+0x58/0x70 mm/kasan/generic.c:587
kasan_save_free_info mm/kasan/kasan.h:406 [inline]
poison_slab_object mm/kasan/common.c:252 [inline]
__kasan_slab_free+0x74/0xa4 mm/kasan/common.c:284
kasan_slab_free include/linux/kasan.h:234 [inline]
slab_free_hook mm/slub.c:2523 [inline]
slab_free mm/slub.c:6611 [inline]
kfree+0x184/0x600 mm/slub.c:6818
qfq_change_class+0x92c/0xbe8 net/sched/sch_qfq.c:533
__tc_ctl_tclass net/sched/sch_api.c:2274 [inline]
tc_ctl_tclass+0x988/0x10b0 net/sched/sch_api.c:2304
rtnetlink_rcv_msg+0x624/0x97c net/core/rtnetlink.c:6963
netlink_rcv_skb+0x220/0x3fc net/netlink/af_netlink.c:2552
rtnetlink_rcv+0x28/0x38 net/core/rtnetlink.c:6981
netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
netlink_unicast+0x694/0x8c4 net/netlink/af_netlink.c:1346
netlink_sendmsg+0x648/0x930 net/netlink/af_netlink.c:1896
sock_sendmsg_nosec net/socket.c:727 [inline]
__sock_sendmsg net/socket.c:742 [inline]
____sys_sendmsg+0x490/0x7b8 net/socket.c:2630
___sys_sendmsg+0x204/0x278 net/socket.c:2684
__sys_sendmsg net/socket.c:2716 [inline]
__do_sys_sendmsg net/socket.c:2721 [inline]
__se_sys_sendmsg net/socket.c:2719 [inline]
__arm64_sys_sendmsg+0x184/0x238 net/socket.c:2719
__invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
invoke_syscall+0x98/0x254 arch/arm64/kernel/syscall.c:49
el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:132
do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
el0_svc+0x5c/0x254 arch/arm64/kernel/entry-common.c:746
el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:765
el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596

The buggy address belongs to the object at ffff0000ca2bfe00
which belongs to the cache kmalloc-128 of size 128
The buggy address is located 80 bytes inside of
freed 128-byte region [ffff0000ca2bfe00, ffff0000ca2bfe80)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x10a2bf
flags: 0x5ffc00000000000(node=0|zone=2|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 05ffc00000000000 ffff0000c0001a00 dead000000000122 0000000000000000
raw: 0000000000000000 0000000080100010 00000000f5000000 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
ffff0000ca2bfd00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 fc
ffff0000ca2bfd80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff0000ca2bfe00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff0000ca2bfe80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff0000ca2bff00: 00 00 00 00 00 00 00 00 00 00 00 00 00 fc fc fc
==================================================================
Unable to handle kernel paging request at virtual address 006a007b60000350
Mem abort info:
ESR = 0x0000000096000004
EC = 0x25: DABT (current EL), IL = 32 bits
SET = 0, FnV = 0
EA = 0, S1PTW = 0
FSC = 0x04: level 0 translation fault
Data abort info:
ISV = 0, ISS = 0x00000004, ISS2 = 0x00000000
CM = 0, WnR = 0, TnD = 0, TagAccess = 0
GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
[006a007b60000350] address between user and kernel address ranges
Internal error: Oops: 0000000096000004 [#1] SMP
Modules linked in:
CPU: 0 UID: 0 PID: 6716 Comm: syz.0.17 Tainted: G B syzkaller #0 PREEMPT
Tainted: [B]=BAD_PAGE
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/30/2025
pstate: 83400005 (Nzcv daif +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
pc : qfq_reset_qdisc+0xbc/0x208 net/sched/sch_qfq.c:1484
lr : qfq_reset_qdisc+0x158/0x208 net/sched/sch_qfq.c:1483
sp : ffff8000a5b577c0
x29: ffff8000a5b577d0 x28: 0000000000000000 x27: 1fffe0001a92d05a
x26: 006a807b60000350 x25: dfff800000000000 x24: 0000000000000000
x23: 035403db00001a84 x22: 035403db00001a34 x21: ffff0000d49682d0
x20: ffff0000d49682d8 x19: ffff0000d4968000 x18: 1fffe000337db690
x17: 3d3d3d3d3d3d3d3d x16: ffff800082de9540 x15: 0000000000000001
x14: 1ffff0001250b1b8 x13: 0000000000000000 x12: 0000000000000000
x11: ffff70001250b1b9 x10: 0000000000ff0100 x9 : 0000000000000000
x8 : ffff0000c9320000 x7 : 0000000000000001 x6 : ffff8000805638d4
x5 : 0000000000000000 x4 : 0000000000000000 x3 : ffff80008936af34
x2 : 0000000000000000 x1 : 0000000000000008 x0 : 0000000000000000
Call trace:
qfq_reset_qdisc+0xbc/0x208 net/sched/sch_qfq.c:1484 (P)
qdisc_reset+0x128/0x598 net/sched/sch_generic.c:1038
__qdisc_destroy+0x134/0x4bc net/sched/sch_generic.c:1077
qdisc_put net/sched/sch_generic.c:1109 [inline]
dev_shutdown+0x35c/0x47c net/sched/sch_generic.c:1497
unregister_netdevice_many_notify+0xbb8/0x1de0 net/core/dev.c:12242
unregister_netdevice_many net/core/dev.c:12317 [inline]
unregister_netdevice_queue+0x2b4/0x300 net/core/dev.c:12161
unregister_netdevice include/linux/netdevice.h:3389 [inline]
__tun_detach+0x5d4/0x1304 drivers/net/tun.c:621
tun_detach drivers/net/tun.c:637 [inline]
tun_chr_close+0x118/0x1f8 drivers/net/tun.c:3436
__fput+0x340/0x75c fs/file_table.c:468
____fput+0x20/0x58 fs/file_table.c:496
task_work_run+0x1dc/0x260 kernel/task_work.c:227
resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
exit_to_user_mode_loop+0xfc/0x178 kernel/entry/common.c:43
exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
arm64_exit_to_user_mode arch/arm64/kernel/entry-common.c:103 [inline]
el0_svc+0x170/0x254 arch/arm64/kernel/entry-common.c:747
el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:765
el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596
Code: d1002116 b4000656 910142d7 d343fefa (38796b48)
---[ end trace 0000000000000000 ]---
----------------
Code disassembly (best guess):
0: d1002116 sub x22, x8, #0x8
4: b4000656 cbz x22, 0xcc
8: 910142d7 add x23, x22, #0x50
c: d343fefa lsr x26, x23, #3
* 10: 38796b48 ldrb w8, [x26, x25] <-- trapping instruction


---
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