[syzbot] [bluetooth?] [bcachefs?] KASAN: slab-use-after-free Read in hci_uart_write_work

syzbot
2025-07-14T17:09:32Z

Hello,

syzbot found the following issue on:

HEAD commit: 3f31a806a62e Merge tag 'mm-hotfixes-stable-2025-07-11-16-1..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=174b07d4580000
kernel config: https://syzkaller.appspot.com/x/.config?x=b309c907eaab29da
dashboard link: https://syzkaller.appspot.com/bug?extid=fde6bd779f78e6e0992e
compiler: Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=127ece8c580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-3f31a806.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/7304d62ced97/vmlinux-3f31a806.xz
kernel image: https://storage.googleapis.com/syzbot-assets/4913df6ab730/bzImage-3f31a806.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/bb03f46b9e61/mount_5.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+fde6bd779f78e6e0992e@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-use-after-free in hci_uart_write_work+0x2ca/0x550 drivers/bluetooth/hci_ldisc.c:165
Read of size 8 at addr ffff8880555a35d8 by task kworker/0:7/5631

CPU: 0 UID: 0 PID: 5631 Comm: kworker/0:7 Not tainted 6.16.0-rc5-syzkaller-00266-g3f31a806a62e #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Workqueue: events hci_uart_write_work
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/0x230 mm/kasan/report.c:480
kasan_report+0x118/0x150 mm/kasan/report.c:593
hci_uart_write_work+0x2ca/0x550 drivers/bluetooth/hci_ldisc.c:165
process_one_work kernel/workqueue.c:3238 [inline]
process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3321
worker_thread+0x8a0/0xda0 kernel/workqueue.c:3402
kthread+0x70e/0x8a0 kernel/kthread.c:464
ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>

Allocated by task 54:
kasan_save_stack mm/kasan/common.c:47 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:68
unpoison_slab_object mm/kasan/common.c:319 [inline]
__kasan_slab_alloc+0x6c/0x80 mm/kasan/common.c:345
kasan_slab_alloc include/linux/kasan.h:250 [inline]
slab_post_alloc_hook mm/slub.c:4148 [inline]
slab_alloc_node mm/slub.c:4197 [inline]
kmem_cache_alloc_node_noprof+0x1bb/0x3c0 mm/slub.c:4249
__alloc_skb+0x112/0x2d0 net/core/skbuff.c:660
alloc_skb include/linux/skbuff.h:1336 [inline]
h5_prepare_pkt+0x184/0x530 drivers/bluetooth/hci_h5.c:702
h5_dequeue+0x197/0x790 drivers/bluetooth/hci_h5.c:761
hci_uart_dequeue drivers/bluetooth/hci_ldisc.c:107 [inline]
hci_uart_write_work+0x24a/0x550 drivers/bluetooth/hci_ldisc.c:161
process_one_work kernel/workqueue.c:3238 [inline]
process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3321
worker_thread+0x8a0/0xda0 kernel/workqueue.c:3402
kthread+0x70e/0x8a0 kernel/kthread.c:464
ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

The buggy address belongs to the object at ffff8880555a3500
which belongs to the cache skbuff_head_cache of size 240
The buggy address is located 216 bytes inside of
freed 240-byte region [ffff8880555a3500, ffff8880555a35f0)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x555a3
flags: 0x4fff00000000000(node=1|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 04fff00000000000 ffff8880304e0b40 dead000000000100 dead000000000122
raw: 0000000000000000 00000000000c000c 00000000f5000000 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0x52cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP), pid 5474, tgid 5474 (syz-executor), ts 183992405509, free_ts 181552341552
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x240/0x2a0 mm/page_alloc.c:1704
prep_new_page mm/page_alloc.c:1712 [inline]
get_page_from_freelist+0x21e4/0x22c0 mm/page_alloc.c:3669
__alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:4959
alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2419
alloc_slab_page mm/slub.c:2451 [inline]
allocate_slab+0x8a/0x3b0 mm/slub.c:2619
new_slab mm/slub.c:2673 [inline]
___slab_alloc+0xbfc/0x1480 mm/slub.c:3859
__slab_alloc mm/slub.c:3949 [inline]
__slab_alloc_node mm/slub.c:4024 [inline]
slab_alloc_node mm/slub.c:4185 [inline]
kmem_cache_alloc_node_noprof+0x280/0x3c0 mm/slub.c:4249
__alloc_skb+0x112/0x2d0 net/core/skbuff.c:660
alloc_skb include/linux/skbuff.h:1336 [inline]
nlmsg_new include/net/netlink.h:1041 [inline]
inet_netconf_notify_devconf+0x173/0x240 net/ipv4/devinet.c:2210
__devinet_sysctl_register+0x3f6/0x470 net/ipv4/devinet.c:2684
devinet_sysctl_register+0x187/0x200 net/ipv4/devinet.c:2718
inetdev_init+0x2b4/0x500 net/ipv4/devinet.c:291
inetdev_event+0x301/0x15b0 net/ipv4/devinet.c:1591
notifier_call_chain+0x1b3/0x3e0 kernel/notifier.c:85
call_netdevice_notifiers_extack net/core/dev.c:2268 [inline]
call_netdevice_notifiers net/core/dev.c:2282 [inline]
register_netdevice+0x1608/0x1ae0 net/core/dev.c:11143
team_newlink+0x114/0x160 drivers/net/team/team_core.c:2231
page last free pid 5407 tgid 5407 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
free_pages_prepare mm/page_alloc.c:1248 [inline]
__free_frozen_pages+0xc71/0xe70 mm/page_alloc.c:2706
vfree+0x25a/0x400 mm/vmalloc.c:3434
kcov_put kernel/kcov.c:439 [inline]
kcov_close+0x28/0x50 kernel/kcov.c:535
__fput+0x449/0xa70 fs/file_table.c:465
task_work_run+0x1d1/0x260 kernel/task_work.c:227
exit_task_work include/linux/task_work.h:40 [inline]
do_exit+0x6b5/0x22e0 kernel/exit.c:964
do_group_exit+0x21c/0x2d0 kernel/exit.c:1105
get_signal+0x1286/0x1340 kernel/signal.c:3034
arch_do_signal_or_restart+0x9a/0x750 arch/x86/kernel/signal.c:337
exit_to_user_mode_loop+0x75/0x110 kernel/entry/common.c:111
exit_to_user_mode_prepare include/linux/entry-common.h:330 [inline]
syscall_exit_to_user_mode_work include/linux/entry-common.h:414 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:449 [inline]
do_syscall_64+0x2bd/0x3b0 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
ffff8880555a3480: 00 00 00 00 00 00 fc fc fc fc fc fc fc fc fc fc
ffff8880555a3500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff8880555a3580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fc fc
^
ffff8880555a3600: fc fc fc fc fc fc fc fc fa fb fb fb fb fb fb fb
ffff8880555a3680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

---
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