KASAN: use-after-free Write in hci_conn_drop

Status: upstream: reported syz repro on 2026/03/12 20:44
Reported-by: syzbot+39c01a9cfb028c5bf498@syzkaller.appspotmail.com
First crash: 193d, last: 69d
Fix bisection: failed (error log)
  
▶ ▼ Bug presence (1)
Date Name Commit Repro Result
2026/08/24 upstream (ToT) 0a0d1d55dad5 syz Didn't crash
▶ ▼ Similar bugs (3)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KASAN: slab-use-after-free Write in hci_conn_drop (2) bluetooth 22 syz, C done 7 923d 1054d 0/29 auto-obsoleted due to no activity on 2024/06/21 00:39
upstream KASAN: slab-use-after-free Write in hci_conn_drop (3) bluetooth prio:high 22 syz, C error 1023 172d 292d 0/29 auto-obsoleted due to no activity on 2026/06/11 08:58
upstream KASAN: slab-use-after-free Write in hci_conn_drop bluetooth 22 1 1223d 1219d 0/29 auto-obsoleted due to no activity on 2023/08/25 20:26

Sample crash report:
==================================================================
BUG: KASAN: use-after-free in instrument_atomic_read_write include/linux/instrumented.h:102 [inline]
BUG: KASAN: use-after-free in atomic_dec_and_test include/linux/atomic/atomic-instrumented.h:575 [inline]
BUG: KASAN: use-after-free in hci_conn_drop+0x34/0x2c0 include/net/bluetooth/hci_core.h:1422
Write of size 4 at addr ffff88802906a010 by task syz.2.591/6827

CPU: 0 PID: 6827 Comm: syz.2.591 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0x188/0x24e lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:316 [inline]
 print_report+0xa8/0x210 mm/kasan/report.c:420
 kasan_report+0x10b/0x140 mm/kasan/report.c:524
 check_region_inline mm/kasan/generic.c:-1 [inline]
 kasan_check_range+0x235/0x290 mm/kasan/generic.c:189
 instrument_atomic_read_write include/linux/instrumented.h:102 [inline]
 atomic_dec_and_test include/linux/atomic/atomic-instrumented.h:575 [inline]
 hci_conn_drop+0x34/0x2c0 include/net/bluetooth/hci_core.h:1422
 sco_chan_del+0xe2/0x1c0 net/bluetooth/sco.c:184
 sco_sock_close net/bluetooth/sco.c:490 [inline]
 sco_sock_release+0xad/0x310 net/bluetooth/sco.c:1276
 __sock_release net/socket.c:654 [inline]
 sock_close+0xd5/0x240 net/socket.c:1399
 __fput+0x22c/0x920 fs/file_table.c:320
 task_work_run+0x1d0/0x260 kernel/task_work.c:203
 get_signal+0x11a6/0x1350 kernel/signal.c:2648
 arch_do_signal_or_restart+0xc4/0x1350 arch/x86/kernel/signal.c:871
 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:292 [inline]
 syscall_exit_to_user_mode+0x16/0x40 kernel/entry/common.c:303
 do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:82
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fa929d9c819
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fa92abb8028 EFLAGS: 00000246 ORIG_RAX: 000000000000002a
RAX: fffffffffffffffc RBX: 00007fa92a015fa0 RCX: 00007fa929d9c819
RDX: 0000000000000008 RSI: 0000200000000040 RDI: 0000000000000004
RBP: 00007fa929e32c91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fa92a016038 R14: 00007fa92a015fa0 R15: 00007ffc0cf4d0b8
 </TASK>

Allocated by task 6827:
 kasan_save_stack mm/kasan/common.c:46 [inline]
 kasan_set_track+0x4b/0x70 mm/kasan/common.c:53
 ____kasan_kmalloc mm/kasan/common.c:375 [inline]
 __kasan_kmalloc+0x8e/0xa0 mm/kasan/common.c:384
 kmalloc include/linux/slab.h:563 [inline]
 kzalloc include/linux/slab.h:699 [inline]
 hci_conn_add+0xb7/0x1390 net/bluetooth/hci_conn.c:990
 hci_connect_sco+0x86/0x330 net/bluetooth/hci_conn.c:1630
 sco_connect net/bluetooth/sco.c:280 [inline]
 sco_sock_connect+0x2d3/0x970 net/bluetooth/sco.c:623
 __sys_connect_file net/socket.c:2010 [inline]
 __sys_connect+0x3cb/0x450 net/socket.c:2027
 __do_sys_connect net/socket.c:2037 [inline]
 __se_sys_connect net/socket.c:2034 [inline]
 __x64_sys_connect+0x76/0x80 net/socket.c:2034
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

Freed by task 6822:
 kasan_save_stack mm/kasan/common.c:46 [inline]
 kasan_set_track+0x4b/0x70 mm/kasan/common.c:53
 kasan_save_free_info+0x2d/0x50 mm/kasan/generic.c:516
 ____kasan_slab_free+0x126/0x1e0 mm/kasan/common.c:237
 kasan_slab_free include/linux/kasan.h:177 [inline]
 slab_free_hook mm/slub.c:1729 [inline]
 slab_free_freelist_hook+0x131/0x1a0 mm/slub.c:1755
 slab_free mm/slub.c:3687 [inline]
 __kmem_cache_free+0xb6/0x1f0 mm/slub.c:3700
 device_release+0x92/0x1c0 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+0x21d/0x460 lib/kobject.c:729
 hci_conn_cleanup+0x575/0x730 net/bluetooth/hci_conn.c:172
 hci_conn_del+0x515/0x720 net/bluetooth/hci_conn.c:1152
 hci_conn_del+0x3c8/0x720 net/bluetooth/hci_conn.c:1111
 hci_abort_conn_sync+0xb3c/0xd50 net/bluetooth/hci_sync.c:5577
 hci_disconnect_all_sync net/bluetooth/hci_sync.c:5590 [inline]
 hci_suspend_sync+0x48a/0xdb0 net/bluetooth/hci_sync.c:6072
 hci_suspend_dev+0x199/0x320 net/bluetooth/hci_core.c:2857
 hci_suspend_notifier+0xc8/0x270 net/bluetooth/hci_core.c:2424
 notifier_call_chain kernel/notifier.c:87 [inline]
 notifier_call_chain_robust+0xe1/0x2c0 kernel/notifier.c:122
 blocking_notifier_call_chain_robust+0x66/0x90 kernel/notifier.c:347
 pm_notifier_call_chain_robust+0x28/0x60 kernel/power/main.c:90
 snapshot_open+0x19b/0x280 kernel/power/user.c:77
 misc_open+0x31f/0x390 drivers/char/misc.c:145
 chrdev_open+0x5c5/0x6a0 fs/char_dev.c:414
 do_dentry_open+0x7e9/0x10d0 fs/open.c:882
 do_open fs/namei.c:3634 [inline]
 path_openat+0x2635/0x2ee0 fs/namei.c:3791
 do_filp_open+0x1f1/0x430 fs/namei.c:3818
 do_sys_openat2+0x150/0x4b0 fs/open.c:1320
 do_sys_open fs/open.c:1336 [inline]
 __do_sys_openat fs/open.c:1352 [inline]
 __se_sys_openat fs/open.c:1347 [inline]
 __x64_sys_openat+0x135/0x160 fs/open.c:1347
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

The buggy address belongs to the object at ffff88802906a000
 which belongs to the cache kmalloc-4k of size 4096
The buggy address is located 16 bytes inside of
 4096-byte region [ffff88802906a000, ffff88802906b000)

The buggy address belongs to the physical page:
page:ffffea0000a41a00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x29068
head:ffffea0000a41a00 order:3 compound_mapcount:0 compound_pincount:0
flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000010200 ffffea0001d7ae00 dead000000000002 ffff888017442140
raw: 0000000000000000 0000000000040004 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0x1d2a20(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 5070, tgid 5070 (kworker/u4:12), ts 145275715495, free_ts 145250339145
 set_page_owner include/linux/page_owner.h:31 [inline]
 post_alloc_hook+0x173/0x1a0 mm/page_alloc.c:2559
 prep_new_page mm/page_alloc.c:2566 [inline]
 get_page_from_freelist+0x1a1e/0x1ab0 mm/page_alloc.c:4357
 __alloc_pages+0x1ec/0x4f0 mm/page_alloc.c:5657
 alloc_slab_page+0x5d/0x160 mm/slub.c:1799
 allocate_slab mm/slub.c:1944 [inline]
 new_slab+0x87/0x2c0 mm/slub.c:1997
 ___slab_alloc+0xbc6/0x1240 mm/slub.c:3154
 __slab_alloc mm/slub.c:3240 [inline]
 slab_alloc_node mm/slub.c:3325 [inline]
 __kmem_cache_alloc_node+0x1a0/0x260 mm/slub.c:3398
 __do_kmalloc_node mm/slab_common.c:935 [inline]
 __kmalloc_node_track_caller+0x9e/0x230 mm/slab_common.c:956
 kmalloc_reserve net/core/skbuff.c:446 [inline]
 __alloc_skb+0x22a/0x7e0 net/core/skbuff.c:515
 alloc_skb include/linux/skbuff.h:1303 [inline]
 nsim_dev_trap_skb_build drivers/net/netdevsim/dev.c:748 [inline]
 nsim_dev_trap_report drivers/net/netdevsim/dev.c:805 [inline]
 nsim_dev_trap_report_work+0x28f/0xaf0 drivers/net/netdevsim/dev.c:851
 process_one_work+0x8a2/0x1160 kernel/workqueue.c:2292
 worker_thread+0xaa2/0x1270 kernel/workqueue.c:2439
 kthread+0x29d/0x330 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:295
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1486 [inline]
 free_pcp_prepare mm/page_alloc.c:1536 [inline]
 free_unref_page_prepare+0x8b4/0x9a0 mm/page_alloc.c:3413
 free_unref_page+0x2e/0x3f0 mm/page_alloc.c:3508
 free_slab mm/slub.c:2036 [inline]
 discard_slab mm/slub.c:2042 [inline]
 __unfreeze_partials+0x1a5/0x200 mm/slub.c:2591
 put_cpu_partial+0x17c/0x250 mm/slub.c:2667
 qlink_free mm/kasan/quarantine.c:168 [inline]
 qlist_free_all+0x76/0xe0 mm/kasan/quarantine.c:187
 kasan_quarantine_reduce+0x144/0x160 mm/kasan/quarantine.c:294
 __kasan_slab_alloc+0x1e/0x80 mm/kasan/common.c:306
 kasan_slab_alloc include/linux/kasan.h:201 [inline]
 slab_post_alloc_hook+0x4b/0x480 mm/slab.h:737
 slab_alloc_node mm/slub.c:3359 [inline]
 slab_alloc mm/slub.c:3367 [inline]
 __kmem_cache_alloc_lru mm/slub.c:3374 [inline]
 kmem_cache_alloc+0x123/0x2f0 mm/slub.c:3383
 getname_flags+0xb7/0x500 fs/namei.c:139
 getname fs/namei.c:218 [inline]
 __do_sys_unlink fs/namei.c:4446 [inline]
 __se_sys_unlink fs/namei.c:4444 [inline]
 __x64_sys_unlink+0x38/0x50 fs/namei.c:4444
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

Memory state around the buggy address:
 ffff888029069f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888029069f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88802906a000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                         ^
 ffff88802906a080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88802906a100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Crashes (6):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/03/29 06:59 linux-6.1.y 1989cd3d56e2 b5ceaad2 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan KASAN: use-after-free Write in hci_conn_drop
2026/07/15 05:21 linux-6.1.y 090666d3cc90 2130f682 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan-arm64 KASAN: use-after-free Write in hci_conn_drop
2026/07/15 05:09 linux-6.1.y 090666d3cc90 2130f682 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan-arm64 KASAN: use-after-free Write in hci_conn_drop
2026/06/24 23:18 linux-6.1.y fdb6fcb41cc7 302586aa .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_drop
2026/06/24 19:19 linux-6.1.y fdb6fcb41cc7 302586aa .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan-arm64 KASAN: use-after-free Write in hci_conn_drop
2026/03/12 20:44 linux-6.1.y f2ddafa93a25 4efadf07 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan-arm64 KASAN: use-after-free Write in hci_conn_drop
* Struck through repros no longer work on HEAD.