KASAN: use-after-free Read in l2cap_connect_cfm (2)

Status: upstream: reported C repro on 2025/09/24 14:26
Bug presence: origin:lts-only
[Documentation on labels]
Reported-by: syzbot+d68bdee064365af6ea43@syzkaller.appspotmail.com
First crash: 314d, last: 48d
Fix bisection: the issue occurs on the latest tested release (bisect log)
Crash: KASAN: use-after-free Read in l2cap_connect_cfm (log)
Repro: C syz .config
  
▶ ▼ Bug presence (2)
Date Name Commit Repro Result
2025/09/26 linux-5.15.y (ToT) 43bb85222e53 C [report] KASAN: use-after-free Read in l2cap_connect_cfm
2025/09/26 upstream (ToT) fec734e8d564 C Didn't crash
▶ ▼ Similar bugs (6)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-6.1 KASAN: wild-memory-access Read in l2cap_connect_cfm 19 7 67d 306d 0/3 upstream: reported on 2025/10/02 10:15
linux-5.15 KASAN: use-after-free Read in l2cap_connect_cfm 19 3 446d 545d 0/3 auto-obsoleted due to no activity on 2025/08/23 07:27
linux-6.1 KASAN: use-after-free Read in l2cap_connect_cfm 19 6 433d 654d 0/3 auto-obsoleted due to no activity on 2025/09/05 21:35
upstream KASAN: slab-use-after-free Read in l2cap_connect_cfm bluetooth 19 syz inconclusive 36 516d 595d 0/29 closed as invalid on 2025/03/07 00:26
upstream KASAN: wild-memory-access Read in l2cap_connect_cfm prio:high bluetooth 19 syz, C error inconclusive 345 37d 505d 0/29 upstream: reported C repro on 2025/03/17 15:57
linux-6.6 KASAN: slab-use-after-free Read in l2cap_connect_cfm origin:upstream 19 syz, C error 23 47d 320d 0/2 upstream: reported C repro on 2025/09/18 08:10
▶ ▼ Last patch testing requests (3)
Created Duration User Patch Repo Result
2026/06/15 05:23 25m retest repro linux-5.15.y report log
2026/04/01 03:17 1h11m retest repro linux-5.15.y report log
2026/01/20 20:18 15m retest repro linux-5.15.y report log
▶ ▼ Fix bisection attempts (7)
Created Duration User Patch Repo Result
2026/06/22 03:59 12h39m fix candidate upstream error job log
2026/04/24 10:12 16m fix candidate upstream error job log
2026/03/24 19:32 1m fix candidate upstream error job log
2026/02/22 19:16 1m fix candidate upstream error job log
2026/01/23 06:47 1m fix candidate upstream error job log
2025/11/16 20:38 12h05m fix candidate upstream error job log
2025/11/06 08:24 2h17m bisect fix linux-5.15.y OK (0) job log log

Sample crash report:
 </TASK>
kobject_add_internal failed for hci0:201 with -EEXIST, don't try to register things with the same name in the same directory.
Bluetooth: hci0: failed to register connection device
==================================================================
BUG: KASAN: use-after-free in l2cap_conn_ready net/bluetooth/l2cap_core.c:1758 [inline]
BUG: KASAN: use-after-free in l2cap_connect_cfm+0x6ff/0x10d0 net/bluetooth/l2cap_core.c:8320
Read of size 8 at addr ffff88807bfde488 by task kworker/u5:1/4264

CPU: 0 PID: 4264 Comm: kworker/u5:1 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
Workqueue: hci0 hci_rx_work
Call Trace:
 <TASK>
 dump_stack_lvl+0x168/0x230 lib/dump_stack.c:106
 print_address_description+0x60/0x2d0 mm/kasan/report.c:248
 __kasan_report mm/kasan/report.c:434 [inline]
 kasan_report+0xdf/0x130 mm/kasan/report.c:451
 l2cap_conn_ready net/bluetooth/l2cap_core.c:1758 [inline]
 l2cap_connect_cfm+0x6ff/0x10d0 net/bluetooth/l2cap_core.c:8320
 hci_connect_cfm include/net/bluetooth/hci_core.h:1505 [inline]
 le_conn_complete_evt+0xdaf/0x1590 net/bluetooth/hci_event.c:5439
 hci_le_conn_complete_evt net/bluetooth/hci_event.c:5464 [inline]
 hci_le_meta_evt+0x289/0x3b80 net/bluetooth/hci_event.c:6186
 hci_event_packet+0xe05/0x12f0 net/bluetooth/hci_event.c:6535
 hci_rx_work+0x255/0xa10 net/bluetooth/hci_core.c:5160
 process_one_work+0x863/0x1000 kernel/workqueue.c:2310
 worker_thread+0xaa8/0x12a0 kernel/workqueue.c:2457
 kthread+0x436/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
 </TASK>

Allocated by task 4264:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track mm/kasan/common.c:46 [inline]
 set_alloc_info mm/kasan/common.c:434 [inline]
 ____kasan_kmalloc mm/kasan/common.c:513 [inline]
 __kasan_kmalloc+0xb5/0xf0 mm/kasan/common.c:522
 kmalloc include/linux/slab.h:604 [inline]
 kzalloc include/linux/slab.h:735 [inline]
 l2cap_chan_create+0x4c/0x730 net/bluetooth/l2cap_core.c:469
 l2cap_sock_alloc+0x13a/0x200 net/bluetooth/l2cap_sock.c:1882
 l2cap_sock_new_connection_cb+0xd1/0x1c0 net/bluetooth/l2cap_sock.c:1479
 l2cap_connect_cfm+0x35d/0x10d0 net/bluetooth/l2cap_core.c:8303
 hci_connect_cfm include/net/bluetooth/hci_core.h:1505 [inline]
 le_conn_complete_evt+0xdaf/0x1590 net/bluetooth/hci_event.c:5439
 hci_le_conn_complete_evt net/bluetooth/hci_event.c:5464 [inline]
 hci_le_meta_evt+0x289/0x3b80 net/bluetooth/hci_event.c:6186
 hci_event_packet+0xe05/0x12f0 net/bluetooth/hci_event.c:6535
 hci_rx_work+0x255/0xa10 net/bluetooth/hci_core.c:5160
 process_one_work+0x863/0x1000 kernel/workqueue.c:2310
 worker_thread+0xaa8/0x12a0 kernel/workqueue.c:2457
 kthread+0x436/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287

Freed by task 4357:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track+0x4b/0x70 mm/kasan/common.c:46
 kasan_set_free_info+0x1f/0x40 mm/kasan/generic.c:360
 ____kasan_slab_free+0xd5/0x110 mm/kasan/common.c:366
 kasan_slab_free include/linux/kasan.h:230 [inline]
 slab_free_hook mm/slub.c:1710 [inline]
 slab_free_freelist_hook+0xea/0x170 mm/slub.c:1736
 slab_free mm/slub.c:3504 [inline]
 kfree+0xef/0x2a0 mm/slub.c:4564
 l2cap_sock_cleanup_listen+0xea/0x270 net/bluetooth/l2cap_sock.c:1462
 l2cap_sock_release+0x66/0x1e0 net/bluetooth/l2cap_sock.c:1420
 __sock_release net/socket.c:649 [inline]
 sock_close+0xd5/0x240 net/socket.c:1336
 __fput+0x234/0x930 fs/file_table.c:311
 task_work_run+0x125/0x1a0 kernel/task_work.c:188
 tracehook_notify_resume include/linux/tracehook.h:189 [inline]
 exit_to_user_mode_loop+0x10f/0x130 kernel/entry/common.c:181
 exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:214
 __syscall_exit_to_user_mode_work kernel/entry/common.c:296 [inline]
 syscall_exit_to_user_mode+0x16/0x40 kernel/entry/common.c:307
 do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x66/0xd0

The buggy address belongs to the object at ffff88807bfde000
 which belongs to the cache kmalloc-2k of size 2048
The buggy address is located 1160 bytes inside of
 2048-byte region [ffff88807bfde000, ffff88807bfde800)
The buggy address belongs to the page:
page:ffffea0001eff600 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x7bfd8
head:ffffea0001eff600 order:3 compound_mapcount:0 compound_pincount:0
flags: 0xfff00000010200(slab|head|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000010200 0000000000000000 dead000000000122 ffff888016842000
raw: 0000000000000000 0000000080080008 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 0x152a20(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_HARDWALL), pid 4264, ts 80764463869, free_ts 80463257214
 prep_new_page mm/page_alloc.c:2426 [inline]
 get_page_from_freelist+0x1b77/0x1c60 mm/page_alloc.c:4192
 __alloc_pages+0x1e1/0x470 mm/page_alloc.c:5487
 alloc_slab_page mm/slub.c:1780 [inline]
 allocate_slab mm/slub.c:1917 [inline]
 new_slab+0xc0/0x4b0 mm/slub.c:1980
 ___slab_alloc+0x81e/0xdf0 mm/slub.c:3013
 __slab_alloc mm/slub.c:3100 [inline]
 slab_alloc_node mm/slub.c:3191 [inline]
 slab_alloc mm/slub.c:3233 [inline]
 kmem_cache_alloc_trace+0x1a5/0x2a0 mm/slub.c:3250
 kmalloc include/linux/slab.h:604 [inline]
 kzalloc include/linux/slab.h:735 [inline]
 l2cap_chan_create+0x4c/0x730 net/bluetooth/l2cap_core.c:469
 l2cap_sock_alloc+0x13a/0x200 net/bluetooth/l2cap_sock.c:1882
 l2cap_sock_new_connection_cb+0xd1/0x1c0 net/bluetooth/l2cap_sock.c:1479
 l2cap_connect_cfm+0x35d/0x10d0 net/bluetooth/l2cap_core.c:8303
 hci_connect_cfm include/net/bluetooth/hci_core.h:1505 [inline]
 le_conn_complete_evt+0xdaf/0x1590 net/bluetooth/hci_event.c:5439
 hci_le_conn_complete_evt net/bluetooth/hci_event.c:5464 [inline]
 hci_le_meta_evt+0x289/0x3b80 net/bluetooth/hci_event.c:6186
 hci_event_packet+0xe05/0x12f0 net/bluetooth/hci_event.c:6535
 hci_rx_work+0x255/0xa10 net/bluetooth/hci_core.c:5160
 process_one_work+0x863/0x1000 kernel/workqueue.c:2310
 worker_thread+0xaa8/0x12a0 kernel/workqueue.c:2457
 kthread+0x436/0x520 kernel/kthread.c:334
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1340 [inline]
 free_pcp_prepare mm/page_alloc.c:1391 [inline]
 free_unref_page_prepare+0x637/0x6c0 mm/page_alloc.c:3317
 free_unref_page+0x94/0x280 mm/page_alloc.c:3396
 free_slab mm/slub.c:2020 [inline]
 discard_slab mm/slub.c:2026 [inline]
 __unfreeze_partials+0x1a5/0x200 mm/slub.c:2512
 put_cpu_partial+0x12d/0x190 mm/slub.c:2592
 qlist_free_all+0x35/0x90 mm/kasan/quarantine.c:176
 kasan_quarantine_reduce+0x150/0x160 mm/kasan/quarantine.c:283
 __kasan_slab_alloc+0x2f/0xd0 mm/kasan/common.c:444
 kasan_slab_alloc include/linux/kasan.h:254 [inline]
 slab_post_alloc_hook+0x4c/0x380 mm/slab.h:519
 slab_alloc_node mm/slub.c:3225 [inline]
 slab_alloc mm/slub.c:3233 [inline]
 kmem_cache_alloc+0x100/0x290 mm/slub.c:3238
 ptlock_alloc+0x1c/0x60 mm/memory.c:5556
 ptlock_init include/linux/mm.h:2241 [inline]
 pgtable_pte_page_ctor include/linux/mm.h:2268 [inline]
 __pte_alloc_one include/asm-generic/pgalloc.h:66 [inline]
 pte_alloc_one+0xc5/0x2f0 arch/x86/mm/pgtable.c:33
 do_fault_around mm/memory.c:4237 [inline]
 do_read_fault mm/memory.c:4258 [inline]
 do_fault mm/memory.c:4392 [inline]
 handle_pte_fault mm/memory.c:4650 [inline]
 __handle_mm_fault mm/memory.c:4785 [inline]
 handle_mm_fault+0x2518/0x43c0 mm/memory.c:4883
 do_user_addr_fault+0x489/0xc80 arch/x86/mm/fault.c:1357
 handle_page_fault arch/x86/mm/fault.c:1445 [inline]
 exc_page_fault+0x60/0x100 arch/x86/mm/fault.c:1501
 asm_exc_page_fault+0x22/0x30 arch/x86/include/asm/idtentry.h:606

Memory state around the buggy address:
 ffff88807bfde380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88807bfde400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88807bfde480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                      ^
 ffff88807bfde500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88807bfde580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Crashes (17):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/09/25 00:04 linux-5.15.y 43bb85222e53 0abd0691 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in l2cap_connect_cfm
2026/06/17 23:26 linux-5.15.y dc027a595035 b62b3ded .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in l2cap_connect_cfm
2026/05/22 23:29 linux-5.15.y 93741761e5e3 5f091fcc .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in l2cap_connect_cfm
2026/05/19 12:27 linux-5.15.y 93741761e5e3 223544dc .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in l2cap_connect_cfm
2026/05/16 14:49 linux-5.15.y 93741761e5e3 a15a64a6 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in l2cap_connect_cfm
2026/05/06 22:46 linux-5.15.y ef251c45f1cd 1dddfd3d .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in l2cap_connect_cfm
2026/02/20 10:43 linux-5.15.y 3330a8d33e08 17d780d6 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in l2cap_connect_cfm
2026/02/19 11:49 linux-5.15.y e45d5d41c134 746545b8 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in l2cap_connect_cfm
2026/02/19 11:49 linux-5.15.y e45d5d41c134 746545b8 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in l2cap_connect_cfm
2026/02/19 08:52 linux-5.15.y e45d5d41c134 746545b8 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in l2cap_connect_cfm
2026/02/07 04:13 linux-5.15.y 7b232985052f f20fc9f9 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in l2cap_connect_cfm
2026/01/28 02:13 linux-5.15.y 9eec9a14ee10 3029c699 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in l2cap_connect_cfm
2026/01/26 19:14 linux-5.15.y 9eec9a14ee10 a4c52dd6 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in l2cap_connect_cfm
2026/01/23 16:11 linux-5.15.y 9eec9a14ee10 e2b1b6e6 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in l2cap_connect_cfm
2025/12/16 14:41 linux-5.15.y 68efe5a6c16a d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in l2cap_connect_cfm
2025/09/25 04:25 linux-5.15.y 43bb85222e53 0abd0691 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in l2cap_connect_cfm
2025/09/24 14:25 linux-5.15.y 43bb85222e53 0abd0691 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan KASAN: use-after-free Read in l2cap_connect_cfm
* Struck through repros no longer work on HEAD.