[syzbot] [bluetooth?] KASAN: slab-use-after-free Read in l2cap_disconn_ind (2)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 8d245acc1e88 Merge tag 'char-misc-6.17-rc3' of git://git.k..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=146067bc580000
kernel config: https://syzkaller.appspot.com/x/.config?x=292f3bc9f654adeb
dashboard link: https://syzkaller.appspot.com/bug?extid=97d2b6a9ca6a6e0f204c
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/924cb94b3bad/disk-8d245acc.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/df04a64e8404/vmlinux-8d245acc.xz
kernel image: https://storage.googleapis.com/syzbot-assets/92335877cbf3/bzImage-8d245acc.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+97d2b6...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-use-after-free in l2cap_disconn_ind+0x79/0xc0 net/bluetooth/l2cap_core.c:7315
Read of size 1 at addr ffff8880574a22b0 by task kworker/u9:2/5864

CPU: 0 UID: 0 PID: 5864 Comm: kworker/u9:2 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
Workqueue: hci3 hci_conn_timeout
Call Trace:
<TASK>
dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
print_address_description mm/kasan/report.c:378 [inline]
print_report+0xca/0x240 mm/kasan/report.c:482
kasan_report+0x118/0x150 mm/kasan/report.c:595
l2cap_disconn_ind+0x79/0xc0 net/bluetooth/l2cap_core.c:7315
hci_proto_disconn_ind include/net/bluetooth/hci_core.h:2058 [inline]
hci_conn_timeout+0xdd/0x290 net/bluetooth/hci_conn.c:581
process_one_work kernel/workqueue.c:3236 [inline]
process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3319
worker_thread+0x8a0/0xda0 kernel/workqueue.c:3400
kthread+0x70e/0x8a0 kernel/kthread.c:463
ret_from_fork+0x3f9/0x770 arch/x86/kernel/process.c:148
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>

Allocated by task 12107:
kasan_save_stack mm/kasan/common.c:47 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:68
poison_kmalloc_redzone mm/kasan/common.c:388 [inline]
__kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:405
kasan_kmalloc include/linux/kasan.h:260 [inline]
__kmalloc_cache_noprof+0x230/0x3d0 mm/slub.c:4396
kmalloc_noprof include/linux/slab.h:905 [inline]
kzalloc_noprof include/linux/slab.h:1039 [inline]
l2cap_conn_add+0xaa/0x8d0 net/bluetooth/l2cap_core.c:6886
l2cap_chan_connect+0x6c8/0xe30 net/bluetooth/l2cap_core.c:7077
bt_6lowpan_connect net/bluetooth/6lowpan.c:900 [inline]
lowpan_control_write+0x421/0x6c0 net/bluetooth/6lowpan.c:1135
full_proxy_write+0x124/0x1f0 fs/debugfs/file.c:388
vfs_write+0x27b/0xb30 fs/read_write.c:684
ksys_write+0x145/0x250 fs/read_write.c:738
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 12409:
kasan_save_stack mm/kasan/common.c:47 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:68
kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:576
poison_slab_object mm/kasan/common.c:243 [inline]
__kasan_slab_free+0x5b/0x80 mm/kasan/common.c:275
kasan_slab_free include/linux/kasan.h:233 [inline]
slab_free_hook mm/slub.c:2417 [inline]
slab_free mm/slub.c:4680 [inline]
kfree+0x18e/0x440 mm/slub.c:4879
l2cap_connect_cfm+0x11d/0x1040 net/bluetooth/l2cap_core.c:7259
hci_connect_cfm include/net/bluetooth/hci_core.h:2082 [inline]
hci_conn_failed+0x1cb/0x310 net/bluetooth/hci_conn.c:1289
hci_abort_conn_sync+0x658/0xe30 net/bluetooth/hci_sync.c:5689
hci_disconnect_all_sync+0x1b5/0x350 net/bluetooth/hci_sync.c:5712
hci_suspend_sync+0x3fc/0xc60 net/bluetooth/hci_sync.c:6188
hci_suspend_dev+0x28d/0x4d0 net/bluetooth/hci_core.c:2849
hci_suspend_notifier+0xf2/0x290 net/bluetooth/hci_core.c:2420
notifier_call_chain+0x1b3/0x3e0 kernel/notifier.c:85
notifier_call_chain_robust kernel/notifier.c:120 [inline]
blocking_notifier_call_chain_robust+0x85/0x100 kernel/notifier.c:345
pm_notifier_call_chain_robust+0x2c/0x60 kernel/power/main.c:103
snapshot_open+0x19c/0x280 kernel/power/user.c:77
misc_open+0x2bc/0x330 drivers/char/misc.c:161
chrdev_open+0x4c9/0x5e0 fs/char_dev.c:414
do_dentry_open+0x950/0x13f0 fs/open.c:965
vfs_open+0x3b/0x340 fs/open.c:1095
do_open fs/namei.c:3887 [inline]
path_openat+0x2ee5/0x3830 fs/namei.c:4046
do_filp_open+0x1fa/0x410 fs/namei.c:4073
do_sys_openat2+0x121/0x1c0 fs/open.c:1435
do_sys_open fs/open.c:1450 [inline]
__do_sys_openat fs/open.c:1466 [inline]
__se_sys_openat fs/open.c:1461 [inline]
__x64_sys_openat+0x138/0x170 fs/open.c:1461
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff8880574a2000
which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 688 bytes inside of
freed 1024-byte region [ffff8880574a2000, ffff8880574a2400)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x574a0
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
ksm flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000040 ffff88801a441dc0 ffffea0000a4d200 dead000000000003
raw: 0000000000000000 0000000000100010 00000000f5000000 0000000000000000
head: 00fff00000000040 ffff88801a441dc0 ffffea0000a4d200 dead000000000003
head: 0000000000000000 0000000000100010 00000000f5000000 0000000000000000
head: 00fff00000000003 ffffea00015d2801 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000008
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0x52820(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP), pid 4890, tgid 4890 (kworker/u8:8), ts 90724194100, free_ts 25796139807
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x240/0x2a0 mm/page_alloc.c:1851
prep_new_page mm/page_alloc.c:1859 [inline]
get_page_from_freelist+0x21e4/0x22c0 mm/page_alloc.c:3858
__alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5148
alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2416
alloc_slab_page mm/slub.c:2487 [inline]
allocate_slab+0x8a/0x370 mm/slub.c:2655
new_slab mm/slub.c:2709 [inline]
___slab_alloc+0xbeb/0x1410 mm/slub.c:3891
__slab_alloc mm/slub.c:3981 [inline]
__slab_alloc_node mm/slub.c:4056 [inline]
slab_alloc_node mm/slub.c:4217 [inline]
__do_kmalloc_node mm/slub.c:4364 [inline]
__kmalloc_noprof+0x305/0x4f0 mm/slub.c:4377
kmalloc_noprof include/linux/slab.h:909 [inline]
kzalloc_noprof include/linux/slab.h:1039 [inline]
neigh_alloc net/core/neighbour.c:522 [inline]
___neigh_create+0x6d5/0x2260 net/core/neighbour.c:656
ip6_finish_output2+0xb4d/0x16a0 net/ipv6/ip6_output.c:132
NF_HOOK include/linux/netfilter.h:318 [inline]
ndisc_send_skb+0xb54/0x1440 net/ipv6/ndisc.c:512
addrconf_dad_completed+0x7ae/0xd60 net/ipv6/addrconf.c:4360
addrconf_dad_work+0xc36/0x14b0 net/ipv6/addrconf.c:-1
process_one_work kernel/workqueue.c:3236 [inline]
process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3319
worker_thread+0x8a0/0xda0 kernel/workqueue.c:3400
kthread+0x70e/0x8a0 kernel/kthread.c:463
ret_from_fork+0x3f9/0x770 arch/x86/kernel/process.c:148
page last free pid 1 tgid 1 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
free_pages_prepare mm/page_alloc.c:1395 [inline]
__free_frozen_pages+0xbc4/0xd30 mm/page_alloc.c:2895
__free_pages mm/page_alloc.c:5260 [inline]
free_contig_range+0x1bd/0x4a0 mm/page_alloc.c:7091
destroy_args+0x69/0x660 mm/debug_vm_pgtable.c:958
debug_vm_pgtable+0x39f/0x3b0 mm/debug_vm_pgtable.c:1345
do_one_initcall+0x233/0x820 init/main.c:1269
do_initcall_level+0x104/0x190 init/main.c:1331
do_initcalls+0x59/0xa0 init/main.c:1347
kernel_init_freeable+0x334/0x4b0 init/main.c:1579
kernel_init+0x1d/0x1d0 init/main.c:1469
ret_from_fork+0x3f9/0x770 arch/x86/kernel/process.c:148
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Memory state around the buggy address:
ffff8880574a2180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8880574a2200: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8880574a2280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff8880574a2300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff8880574a2380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


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