KASAN: use-after-free Write in hci_conn_hash_flush (3)

Status: upstream: reported syz repro on 2026/05/20 21:49
Bug presence: origin:lts-only
[Documentation on labels]
Reported-by: syzbot+fc62153daf5ea5a34579@syzkaller.appspotmail.com
First crash: 148d, last: 48d
Fix bisection: failed (error log)
  
▶ ▼ Bug presence (2)
Date Name Commit Repro Result
2026/08/28 linux-6.1.y (ToT) d64a499eea6b syz [report] KASAN: use-after-free Write in hci_conn_hash_flush
2026/08/28 upstream (ToT) 548e7bcd0c54 syz Didn't crash
▶ ▼ Similar bugs (3)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-6.1 KASAN: use-after-free Write in hci_conn_hash_flush 22 4 480d 634d 0/3 auto-obsoleted due to no activity on 2025/09/30 18:03
linux-6.1 KASAN: use-after-free Write in hci_conn_hash_flush (2) 22 1 358d 358d 0/3 auto-obsoleted due to no activity on 2026/01/30 19:02
upstream KASAN: slab-use-after-free Read in hci_conn_hash_flush bluetooth 22 syz, C error 3511 1228d 1321d 22/29 fixed on 2023/07/01 16:05
▶ ▼ Fix bisection attempts (2)
Created Duration User Patch Repo Result
2026/08/09 13:46 0m bisect fix linux-6.1.y error
2026/06/25 12:55 2h57m bisect fix linux-6.1.y OK (0) job log log

Sample crash report:
==================================================================
BUG: KASAN: use-after-free in hci_conn_unlink net/bluetooth/hci_conn.c:1085 [inline]
BUG: KASAN: use-after-free in hci_conn_hash_flush+0x1b0/0x26c net/bluetooth/hci_conn.c:2510
Write of size 8 at addr ffff0000f173cac8 by task syz-executor/25607

CPU: 0 PID: 25607 Comm: syz-executor Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
Call trace:
 dump_backtrace+0x1c0/0x1ec arch/arm64/kernel/stacktrace.c:158
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:165
 __dump_stack+0x30/0x40 lib/dump_stack.c:88
 dump_stack_lvl+0xf4/0x15c lib/dump_stack.c:106
 print_address_description+0x88/0x218 mm/kasan/report.c:316
 print_report+0x50/0x68 mm/kasan/report.c:420
 kasan_report+0xa8/0xfc mm/kasan/report.c:524
 __asan_report_store8_noabort+0x2c/0x38 mm/kasan/report_generic.c:356
 hci_conn_unlink net/bluetooth/hci_conn.c:1085 [inline]
 hci_conn_hash_flush+0x1b0/0x26c net/bluetooth/hci_conn.c:2510
 hci_dev_close_sync+0x7e0/0xee8 net/bluetooth/hci_sync.c:5247
 hci_dev_do_close net/bluetooth/hci_core.c:528 [inline]
 hci_unregister_dev+0x214/0x4c0 net/bluetooth/hci_core.c:2731
 vhci_release+0x7c/0xcc drivers/bluetooth/hci_vhci.c:573
 __fput+0x1bc/0x7b8 fs/file_table.c:320
 ____fput+0x20/0x30 fs/file_table.c:348
 task_work_run+0x1ec/0x278 kernel/task_work.c:203
 exit_task_work include/linux/task_work.h:39 [inline]
 do_exit+0x550/0x19b0 kernel/exit.c:881
 do_group_exit+0x194/0x22c kernel/exit.c:1023
 get_signal+0x11cc/0x1304 kernel/signal.c:2871
 do_signal arch/arm64/kernel/signal.c:1095 [inline]
 do_notify_resume+0x33c/0x2aa4 arch/arm64/kernel/signal.c:1148
 prepare_exit_to_user_mode arch/arm64/kernel/entry-common.c:137 [inline]
 exit_to_user_mode arch/arm64/kernel/entry-common.c:142 [inline]
 el0_svc+0x98/0x128 arch/arm64/kernel/entry-common.c:638
 el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
 el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

Allocated by task 25620:
 kasan_save_stack mm/kasan/common.c:46 [inline]
 kasan_set_track+0x4c/0x80 mm/kasan/common.c:53
 kasan_save_alloc_info+0x24/0x30 mm/kasan/generic.c:505
 ____kasan_kmalloc mm/kasan/common.c:375 [inline]
 __kasan_kmalloc+0xa0/0xb8 mm/kasan/common.c:384
 kasan_kmalloc include/linux/kasan.h:211 [inline]
 kmalloc_trace+0x7c/0x94 mm/slab_common.c:1031
 kmalloc include/linux/slab.h:563 [inline]
 kzalloc include/linux/slab.h:699 [inline]
 hci_conn_add+0xc4/0x106c net/bluetooth/hci_conn.c:990
 hci_connect_sco+0x94/0x368 net/bluetooth/hci_conn.c:1630
 sco_connect net/bluetooth/sco.c:280 [inline]
 sco_sock_connect+0x260/0x748 net/bluetooth/sco.c:643
 __sys_connect_file net/socket.c:2010 [inline]
 __sys_connect+0x28c/0x2b4 net/socket.c:2027
 __do_sys_connect net/socket.c:2037 [inline]
 __se_sys_connect net/socket.c:2034 [inline]
 __arm64_sys_connect+0x7c/0x94 net/socket.c:2034
 __invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
 invoke_syscall+0x98/0x2b4 arch/arm64/kernel/syscall.c:52
 el0_svc_common+0x138/0x258 arch/arm64/kernel/syscall.c:140
 do_el0_svc+0x58/0x130 arch/arm64/kernel/syscall.c:204
 el0_svc+0x58/0x128 arch/arm64/kernel/entry-common.c:637
 el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
 el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

Freed by task 25607:
 kasan_save_stack mm/kasan/common.c:46 [inline]
 kasan_set_track+0x4c/0x80 mm/kasan/common.c:53
 kasan_save_free_info+0x38/0x5c mm/kasan/generic.c:516
 ____kasan_slab_free+0x148/0x1b0 mm/kasan/common.c:237
 __kasan_slab_free+0x18/0x28 mm/kasan/common.c:245
 kasan_slab_free include/linux/kasan.h:177 [inline]
 slab_free_hook mm/slub.c:1729 [inline]
 slab_free_freelist_hook+0x16c/0x1e8 mm/slub.c:1755
 slab_free mm/slub.c:3687 [inline]
 __kmem_cache_free+0xbc/0x218 mm/slub.c:3700
 kfree+0xd0/0x1a8 mm/slab_common.c:988
 bt_link_release+0x20/0x30 net/bluetooth/hci_sysfs.c:14
 device_release+0x8c/0x1ac drivers/base/core.c:-1
 kobject_cleanup lib/kobject.c:681 [inline]
 kobject_release lib/kobject.c:712 [inline]
 kref_put include/linux/kref.h:65 [inline]
 kobject_put+0x2a8/0x420 lib/kobject.c:729
 put_device+0x28/0x40 drivers/base/core.c:3805
 hci_conn_del_sysfs+0x78/0x14c net/bluetooth/hci_sysfs.c:60
 hci_conn_cleanup+0x4e0/0x68c net/bluetooth/hci_conn.c:172
 hci_conn_del+0x3cc/0x5a4 net/bluetooth/hci_conn.c:1152
 hci_conn_hash_flush+0x1d8/0x26c net/bluetooth/hci_conn.c:2511
 hci_dev_close_sync+0x7e0/0xee8 net/bluetooth/hci_sync.c:5247
 hci_dev_do_close net/bluetooth/hci_core.c:528 [inline]
 hci_unregister_dev+0x214/0x4c0 net/bluetooth/hci_core.c:2731
 vhci_release+0x7c/0xcc drivers/bluetooth/hci_vhci.c:573
 __fput+0x1bc/0x7b8 fs/file_table.c:320
 ____fput+0x20/0x30 fs/file_table.c:348
 task_work_run+0x1ec/0x278 kernel/task_work.c:203
 exit_task_work include/linux/task_work.h:39 [inline]
 do_exit+0x550/0x19b0 kernel/exit.c:881
 do_group_exit+0x194/0x22c kernel/exit.c:1023
 get_signal+0x11cc/0x1304 kernel/signal.c:2871
 do_signal arch/arm64/kernel/signal.c:1095 [inline]
 do_notify_resume+0x33c/0x2aa4 arch/arm64/kernel/signal.c:1148
 prepare_exit_to_user_mode arch/arm64/kernel/entry-common.c:137 [inline]
 exit_to_user_mode arch/arm64/kernel/entry-common.c:142 [inline]
 el0_svc+0x98/0x128 arch/arm64/kernel/entry-common.c:638
 el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
 el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

Last potentially related work creation:
 kasan_save_stack+0x40/0x70 mm/kasan/common.c:46
 __kasan_record_aux_stack+0xc0/0xdc mm/kasan/generic.c:486
 kasan_record_aux_stack_noalloc+0x14/0x20 mm/kasan/generic.c:496
 insert_work+0x64/0x37c kernel/workqueue.c:1361
 __queue_work+0xcbc/0x1234 kernel/workqueue.c:1520
 __queue_delayed_work kernel/workqueue.c:1668 [inline]
 queue_delayed_work_on+0x204/0x30c kernel/workqueue.c:1704
 queue_delayed_work include/linux/workqueue.h:527 [inline]
 hci_conn_drop+0x194/0x2b4 include/net/bluetooth/hci_core.h:1448
 sco_chan_del net/bluetooth/sco.c:184 [inline]
 __sco_sock_close+0x140/0x750 net/bluetooth/sco.c:490
 sco_sock_close net/bluetooth/sco.c:505 [inline]
 sco_sock_release+0xb4/0x2bc net/bluetooth/sco.c:1296
 __sock_release net/socket.c:654 [inline]
 sock_close+0xb4/0x1f8 net/socket.c:1399
 __fput+0x1bc/0x7b8 fs/file_table.c:320
 ____fput+0x20/0x30 fs/file_table.c:348
 task_work_run+0x1ec/0x278 kernel/task_work.c:203
 get_signal+0x111c/0x1304 kernel/signal.c:2648
 do_signal arch/arm64/kernel/signal.c:1095 [inline]
 do_notify_resume+0x33c/0x2aa4 arch/arm64/kernel/signal.c:1148
 prepare_exit_to_user_mode arch/arm64/kernel/entry-common.c:137 [inline]
 exit_to_user_mode arch/arm64/kernel/entry-common.c:142 [inline]
 el0_svc+0x98/0x128 arch/arm64/kernel/entry-common.c:638
 el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
 el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

Second to last potentially related work creation:
 kasan_save_stack+0x40/0x70 mm/kasan/common.c:46
 __kasan_record_aux_stack+0xc0/0xdc mm/kasan/generic.c:486
 kasan_record_aux_stack_noalloc+0x14/0x20 mm/kasan/generic.c:496
 insert_work+0x64/0x37c kernel/workqueue.c:1361
 __queue_work+0xcbc/0x1234 kernel/workqueue.c:1520
 __queue_delayed_work kernel/workqueue.c:1668 [inline]
 queue_delayed_work_on+0x204/0x30c kernel/workqueue.c:1704
 queue_delayed_work include/linux/workqueue.h:527 [inline]
 hci_conn_drop+0x194/0x2b4 include/net/bluetooth/hci_core.h:1448
 sco_chan_del net/bluetooth/sco.c:184 [inline]
 __sco_sock_close+0x140/0x750 net/bluetooth/sco.c:490
 sco_sock_close net/bluetooth/sco.c:505 [inline]
 sco_sock_release+0xb4/0x2bc net/bluetooth/sco.c:1296
 __sock_release net/socket.c:654 [inline]
 sock_close+0xb4/0x1f8 net/socket.c:1399
 __fput+0x1bc/0x7b8 fs/file_table.c:320
 ____fput+0x20/0x30 fs/file_table.c:348
 task_work_run+0x1ec/0x278 kernel/task_work.c:203
 get_signal+0x111c/0x1304 kernel/signal.c:2648
 do_signal arch/arm64/kernel/signal.c:1095 [inline]
 do_notify_resume+0x33c/0x2aa4 arch/arm64/kernel/signal.c:1148
 prepare_exit_to_user_mode arch/arm64/kernel/entry-common.c:137 [inline]
 exit_to_user_mode arch/arm64/kernel/entry-common.c:142 [inline]
 el0_svc+0x98/0x128 arch/arm64/kernel/entry-common.c:638
 el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:655
 el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:585

The buggy address belongs to the object at ffff0000f173c000
 which belongs to the cache kmalloc-4k of size 4096
The buggy address is located 2760 bytes inside of
 4096-byte region [ffff0000f173c000, ffff0000f173d000)

The buggy address belongs to the physical page:
page:0000000037f32110 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x131738
head:0000000037f32110 order:3 compound_mapcount:0 compound_pincount:0
flags: 0x5ffc00000010200(slab|head|node=0|zone=2|lastcpupid=0x7ff)
raw: 05ffc00000010200 dead000000000100 dead000000000122 ffff0000c0002a80
raw: 0000000000000000 0000000000040004 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff0000f173c980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff0000f173ca00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff0000f173ca80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                              ^
 ffff0000f173cb00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff0000f173cb80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/05/20 21:48 linux-6.1.y c27210688955 62fb93a2 .config console log report syz / log [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan-arm64 KASAN: use-after-free Write in hci_conn_hash_flush
* Struck through repros no longer work on HEAD.