[v6.6] KASAN: slab-use-after-free Read in tty_write_room

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 2cf6f68313dc Linux 6.6.122
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=16be153a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=2a950bf7c0bff9f9
dashboard link: https://syzkaller.appspot.com/bug?extid=5522c10517d2f842af95
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/1694df1122d6/disk-2cf6f683.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/d59542417f4c/vmlinux-2cf6f683.xz
kernel image: https://storage.googleapis.com/syzbot-assets/220dc2f6e7ef/bzImage-2cf6f683.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+5522c1...@syzkaller.appspotmail.com

ieee802154 phy0 wpan0: encryption failed: -22
ieee802154 phy1 wpan1: encryption failed: -22
==================================================================
BUG: KASAN: slab-use-after-free in tty_write_room+0x35/0x80 drivers/tty/tty_ioctl.c:72
Read of size 8 at addr ffff888031f74020 by task aoe_tx0/1282

CPU: 1 PID: 1282 Comm: aoe_tx0 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
<TASK>
dump_stack_lvl+0x18c/0x250 lib/dump_stack.c:106
print_address_description mm/kasan/report.c:364 [inline]
print_report+0xa8/0x210 mm/kasan/report.c:468
kasan_report+0x117/0x150 mm/kasan/report.c:581
tty_write_room+0x35/0x80 drivers/tty/tty_ioctl.c:72
handle_tx+0x15e/0x610 drivers/net/caif/caif_serial.c:226
__netdev_start_xmit include/linux/netdevice.h:4943 [inline]
netdev_start_xmit include/linux/netdevice.h:4957 [inline]
xmit_one net/core/dev.c:3658 [inline]
dev_hard_start_xmit+0x246/0x740 net/core/dev.c:3674
__dev_queue_xmit+0x1ac2/0x36b0 net/core/dev.c:4464
dev_queue_xmit include/linux/netdevice.h:3113 [inline]
tx+0x6b/0x180 drivers/block/aoe/aoenet.c:63
kthread+0x1d2/0x3b0 drivers/block/aoe/aoecmd.c:1241
kthread+0x2fa/0x390 kernel/kthread.c:388
ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293
</TASK>

Allocated by task 7632:
kasan_save_stack mm/kasan/common.c:46 [inline]
kasan_set_track+0x4e/0x70 mm/kasan/common.c:53
____kasan_kmalloc mm/kasan/common.c:375 [inline]
__kasan_kmalloc+0x8f/0xa0 mm/kasan/common.c:384
kmalloc include/linux/slab.h:600 [inline]
kzalloc include/linux/slab.h:721 [inline]
alloc_tty_struct+0xa7/0x790 drivers/tty/tty_io.c:3092
tty_init_dev+0x59/0x4c0 drivers/tty/tty_io.c:1407
tty_open_by_driver drivers/tty/tty_io.c:2080 [inline]
tty_open+0x866/0xd80 drivers/tty/tty_io.c:2127
chrdev_open+0x5cc/0x6a0 fs/char_dev.c:414
do_dentry_open+0x8c6/0x1500 fs/open.c:929
do_open fs/namei.c:3640 [inline]
path_openat+0x27f1/0x3230 fs/namei.c:3797
do_filp_open+0x1f5/0x430 fs/namei.c:3824
do_sys_openat2+0x134/0x1d0 fs/open.c:1421
do_sys_open fs/open.c:1436 [inline]
__do_sys_openat fs/open.c:1452 [inline]
__se_sys_openat fs/open.c:1447 [inline]
__x64_sys_openat+0x139/0x160 fs/open.c:1447
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xa0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2

Freed by task 6040:
kasan_save_stack mm/kasan/common.c:46 [inline]
kasan_set_track+0x4e/0x70 mm/kasan/common.c:53
kasan_save_free_info+0x2e/0x50 mm/kasan/generic.c:522
____kasan_slab_free+0x126/0x1e0 mm/kasan/common.c:237
kasan_slab_free include/linux/kasan.h:164 [inline]
slab_free_hook mm/slub.c:1811 [inline]
slab_free_freelist_hook+0x130/0x1a0 mm/slub.c:1837
slab_free mm/slub.c:3830 [inline]
__kmem_cache_free+0xba/0x1e0 mm/slub.c:3843
process_one_work kernel/workqueue.c:2634 [inline]
process_scheduled_works+0xa5d/0x15d0 kernel/workqueue.c:2711
worker_thread+0xa55/0xfc0 kernel/workqueue.c:2792
kthread+0x2fa/0x390 kernel/kthread.c:388
ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293

Last potentially related work creation:
kasan_save_stack+0x3e/0x60 mm/kasan/common.c:46
__kasan_record_aux_stack+0xaf/0xc0 mm/kasan/generic.c:492
insert_work+0x3d/0x310 kernel/workqueue.c:1651
__queue_work+0xc39/0x1020 kernel/workqueue.c:1800
queue_work_on+0x128/0x1f0 kernel/workqueue.c:1835
tty_release_struct+0xb8/0xd0 drivers/tty/tty_io.c:1699
tty_release+0xc79/0x1600 drivers/tty/tty_io.c:1859
__fput+0x234/0x970 fs/file_table.c:384
task_work_run+0x1d4/0x260 kernel/task_work.c:245
exit_task_work include/linux/task_work.h:43 [inline]
do_exit+0x95a/0x2460 kernel/exit.c:883
do_group_exit+0x21b/0x2d0 kernel/exit.c:1024
get_signal+0x12fc/0x13f0 kernel/signal.c:2902
arch_do_signal_or_restart+0xc2/0x800 arch/x86/kernel/signal.c:310
exit_to_user_mode_loop+0x70/0x110 kernel/entry/common.c:174
exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:210
__syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
syscall_exit_to_user_mode+0x1a/0x50 kernel/entry/common.c:302
do_syscall_64+0x61/0xa0 arch/x86/entry/common.c:82
entry_SYSCALL_64_after_hwframe+0x68/0xd2

The buggy address belongs to the object at ffff888031f74000
which belongs to the cache kmalloc-cg-2k of size 2048
The buggy address is located 32 bytes inside of
freed 2048-byte region [ffff888031f74000, ffff888031f74800)

The buggy address belongs to the physical page:
page:ffffea0000c7dc00 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff888031f71000 pfn:0x31f70
head:ffffea0000c7dc00 order:3 entire_mapcount:0 nr_pages_mapped:0 pincount:0
memcg:ffff88802bc5e581
flags: 0xfff00000000840(slab|head|node=0|zone=1|lastcpupid=0x7ff)
page_type: 0xffffffff()
raw: 00fff00000000840 ffff888017c4f3c0 ffffea000171ca10 ffff888017c4e708
raw: ffff888031f71000 0000000000080007 00000001ffffffff ffff88802bc5e581
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 5769, tgid 5769 (syz-executor), ts 88382649638, free_ts 88339136859
set_page_owner include/linux/page_owner.h:31 [inline]
post_alloc_hook+0x1c1/0x200 mm/page_alloc.c:1581
prep_new_page mm/page_alloc.c:1588 [inline]
get_page_from_freelist+0x1951/0x19e0 mm/page_alloc.c:3220
__alloc_pages+0x1f0/0x460 mm/page_alloc.c:4486
alloc_slab_page+0x5d/0x160 mm/slub.c:1881
allocate_slab mm/slub.c:2028 [inline]
new_slab+0x87/0x2d0 mm/slub.c:2081
___slab_alloc+0xc5d/0x12f0 mm/slub.c:3253
__slab_alloc mm/slub.c:3339 [inline]
__slab_alloc_node mm/slub.c:3392 [inline]
slab_alloc_node mm/slub.c:3485 [inline]
__kmem_cache_alloc_node+0x19e/0x250 mm/slub.c:3534
__do_kmalloc_node mm/slab_common.c:1006 [inline]
__kmalloc+0xa4/0x230 mm/slab_common.c:1020
kmalloc include/linux/slab.h:604 [inline]
kzalloc include/linux/slab.h:721 [inline]
__register_sysctl_table+0x6e/0x1240 fs/proc/proc_sysctl.c:1373
__addrconf_sysctl_register+0x27a/0x3f0 net/ipv6/addrconf.c:7210
addrconf_sysctl_register+0x15c/0x1b0 net/ipv6/addrconf.c:7258
addrconf_notify+0x716/0x1010 net/ipv6/addrconf.c:3773
notifier_call_chain+0x197/0x380 kernel/notifier.c:93
call_netdevice_notifiers_extack net/core/dev.c:2103 [inline]
call_netdevice_notifiers net/core/dev.c:2117 [inline]
dev_change_name+0x5e7/0x8c0 net/core/dev.c:1339
do_setlink+0x9fc/0x4130 net/core/rtnetlink.c:2885
__rtnl_newlink net/core/rtnetlink.c:3703 [inline]
rtnl_newlink+0x17da/0x20a0 net/core/rtnetlink.c:3750
page last free stack trace:
reset_page_owner include/linux/page_owner.h:24 [inline]
free_pages_prepare mm/page_alloc.c:1181 [inline]
free_unref_page_prepare+0x7b2/0x8c0 mm/page_alloc.c:2365
free_unref_page+0x32/0x2e0 mm/page_alloc.c:2458
discard_slab mm/slub.c:2127 [inline]
__unfreeze_partials+0x1cf/0x210 mm/slub.c:2667
put_cpu_partial+0x17c/0x250 mm/slub.c:2743
__slab_free+0x319/0x400 mm/slub.c:3700
qlink_free mm/kasan/quarantine.c:166 [inline]
qlist_free_all+0x75/0xd0 mm/kasan/quarantine.c:185
kasan_quarantine_reduce+0x143/0x160 mm/kasan/quarantine.c:292
__kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:306
kasan_slab_alloc include/linux/kasan.h:188 [inline]
slab_post_alloc_hook+0x6e/0x4b0 mm/slab.h:767
slab_alloc_node mm/slub.c:3495 [inline]
__kmem_cache_alloc_node+0x13a/0x250 mm/slub.c:3534
kmalloc_trace+0x2a/0xe0 mm/slab_common.c:1098
kmalloc include/linux/slab.h:600 [inline]
kzalloc include/linux/slab.h:721 [inline]
devlink_trap_group_register net/devlink/trap.c:1555 [inline]
devl_trap_groups_register+0x2f2/0x830 net/devlink/trap.c:1630
nsim_dev_traps_init+0x238/0x490 drivers/net/netdevsim/dev.c:900
nsim_drv_probe+0x67f/0xbb0 drivers/net/netdevsim/dev.c:1578
call_driver_probe drivers/base/dd.c:-1 [inline]
really_probe+0x25b/0xb20 drivers/base/dd.c:658
__driver_probe_device+0x18c/0x330 drivers/base/dd.c:800

Memory state around the buggy address:
ffff888031f73f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff888031f73f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888031f74000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff888031f74080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff888031f74100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


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