KASAN: slab-use-after-free Read in l2cap_connect_cfm

Status: upstream: reported C repro on 2025/09/18 08:10
Bug presence: origin:upstream
[Documentation on labels]
Reported-by: syzbot+e3dee1abcf5ec280b00f@syzkaller.appspotmail.com
First crash: 316d, last: 43d
Fix bisection: failed (error log, bisect log)
  
▶ ▼ Bug presence (1)
Date Name Commit Repro Result
2025/11/02 upstream (ToT) 691d401c7e0e C [report] KASAN: slab-use-after-free Read in l2cap_connect_cfm
▶ ▼ Similar bugs (6)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KASAN: slab-use-after-free Read in l2cap_connect_cfm bluetooth 19 syz inconclusive 36 511d 590d 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 345 32d 500d 0/29 upstream: reported C repro on 2025/03/17 15:57
linux-5.15 KASAN: use-after-free Read in l2cap_connect_cfm (2) origin:lts-only 19 syz, C error 17 43d 309d 0/3 upstream: reported C repro on 2025/09/24 14:26
linux-6.1 KASAN: wild-memory-access Read in l2cap_connect_cfm 19 7 62d 301d 0/3 upstream: reported on 2025/10/02 10:15
linux-5.15 KASAN: use-after-free Read in l2cap_connect_cfm 19 3 442d 540d 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 428d 650d 0/3 auto-obsoleted due to no activity on 2025/09/05 21:35
▶ ▼ Fix bisection attempts (2)
Created Duration User Patch Repo Result
2026/04/23 05:06 14m bisect fix linux-6.6.y error job log
2025/12/09 06:20 3h14m bisect fix linux-6.6.y OK (0) job log log

Sample crash report:
 ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293
 </TASK>
kobject: kobject_add_internal failed for hci1:201 with -EEXIST, don't try to register things with the same name in the same directory.
Bluetooth: hci1: failed to register connection device
==================================================================
BUG: KASAN: slab-use-after-free in l2cap_conn_ready net/bluetooth/l2cap_core.c:1623 [inline]
BUG: KASAN: slab-use-after-free in l2cap_connect_cfm+0x6df/0x1030 net/bluetooth/l2cap_core.c:7275
Read of size 8 at addr ffff88801c6bc480 by task kworker/u5:5/5914

CPU: 1 PID: 5914 Comm: kworker/u5:5 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Workqueue: hci1 hci_rx_work
Call Trace:
 <TASK>
 dump_stack_lvl+0x16c/0x230 lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:364 [inline]
 print_report+0xac/0x220 mm/kasan/report.c:468
 kasan_report+0x117/0x150 mm/kasan/report.c:581
 l2cap_conn_ready net/bluetooth/l2cap_core.c:1623 [inline]
 l2cap_connect_cfm+0x6df/0x1030 net/bluetooth/l2cap_core.c:7275
 hci_connect_cfm+0x8f/0x130 include/net/bluetooth/hci_core.h:1991
 le_conn_complete_evt+0xfb5/0x1500 net/bluetooth/hci_event.c:5772
 hci_le_conn_complete_evt+0x187/0x440 net/bluetooth/hci_event.c:5798
 hci_event_func net/bluetooth/hci_event.c:7440 [inline]
 hci_event_packet+0x795/0x1210 net/bluetooth/hci_event.c:7495
 hci_rx_work+0x43a/0xd80 net/bluetooth/hci_core.c:4018
 process_one_work kernel/workqueue.c:2634 [inline]
 process_scheduled_works+0xa45/0x15b0 kernel/workqueue.c:2711
 worker_thread+0xa55/0xfc0 kernel/workqueue.c:2792
 kthread+0x2fa/0x390 kernel/kthread.c:388
 ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293
 </TASK>

Allocated by task 5914:
 kasan_save_stack mm/kasan/common.c:45 [inline]
 kasan_set_track+0x4e/0x70 mm/kasan/common.c:52
 ____kasan_kmalloc mm/kasan/common.c:374 [inline]
 __kasan_kmalloc+0x8f/0xa0 mm/kasan/common.c:383
 kmalloc include/linux/slab.h:600 [inline]
 kzalloc include/linux/slab.h:721 [inline]
 l2cap_chan_create+0x50/0x760 net/bluetooth/l2cap_core.c:445
 l2cap_sock_alloc net/bluetooth/l2cap_sock.c:1890 [inline]
 l2cap_sock_new_connection_cb+0x182/0x2b0 net/bluetooth/l2cap_sock.c:1469
 l2cap_connect_cfm+0x375/0x1030 net/bluetooth/l2cap_core.c:7258
 hci_connect_cfm+0x8f/0x130 include/net/bluetooth/hci_core.h:1991
 le_conn_complete_evt+0xfb5/0x1500 net/bluetooth/hci_event.c:5772
 hci_le_conn_complete_evt+0x187/0x440 net/bluetooth/hci_event.c:5798
 hci_event_func net/bluetooth/hci_event.c:7440 [inline]
 hci_event_packet+0x795/0x1210 net/bluetooth/hci_event.c:7495
 hci_rx_work+0x43a/0xd80 net/bluetooth/hci_core.c:4018
 process_one_work kernel/workqueue.c:2634 [inline]
 process_scheduled_works+0xa45/0x15b0 kernel/workqueue.c:2711
 worker_thread+0xa55/0xfc0 kernel/workqueue.c:2792
 kthread+0x2fa/0x390 kernel/kthread.c:388
 ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293

Freed by task 6040:
 kasan_save_stack mm/kasan/common.c:45 [inline]
 kasan_set_track+0x4e/0x70 mm/kasan/common.c:52
 kasan_save_free_info+0x2e/0x50 mm/kasan/generic.c:522
 ____kasan_slab_free+0x126/0x1e0 mm/kasan/common.c:236
 kasan_slab_free include/linux/kasan.h:164 [inline]
 slab_free_hook mm/slub.c:1811 [inline]
 slab_free_freelist_hook+0x130/0x1b0 mm/slub.c:1837
 slab_free mm/slub.c:3830 [inline]
 __kmem_cache_free+0xba/0x1f0 mm/slub.c:3843
 l2cap_sock_cleanup_listen+0xea/0x3e0 net/bluetooth/l2cap_sock.c:1452
 l2cap_sock_release+0x6a/0x1e0 net/bluetooth/l2cap_sock.c:1410
 __sock_release net/socket.c:659 [inline]
 sock_close+0xbd/0x230 net/socket.c:1421
 __fput+0x234/0x970 fs/file_table.c:384
 task_work_run+0x1ce/0x250 kernel/task_work.c:239
 resume_user_mode_work include/linux/resume_user_mode.h:49 [inline]
 exit_to_user_mode_loop+0xe6/0x110 kernel/entry/common.c:177
 exit_to_user_mode_prepare+0xf6/0x180 kernel/entry/common.c:210
 __syscall_exit_to_user_mode_work kernel/entry/common.c:291 [inline]
 syscall_exit_to_user_mode+0x1a/0x50 kernel/entry/common.c:302
 do_syscall_64+0x61/0xb0 arch/x86/entry/common.c:87
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

The buggy address belongs to the object at ffff88801c6bc000
 which belongs to the cache kmalloc-2k of size 2048
The buggy address is located 1152 bytes inside of
 freed 2048-byte region [ffff88801c6bc000, ffff88801c6bc800)

The buggy address belongs to the physical page:
page:ffffea000071ae00 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1c6b8
head:ffffea000071ae00 order:3 entire_mapcount:0 nr_pages_mapped:0 pincount:0
anon flags: 0xfff00000000840(slab|head|node=0|zone=1|lastcpupid=0x7ff)
page_type: 0xffffffff()
raw: 00fff00000000840 ffff888017842000 0000000000000000 0000000000000001
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 0x1d20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 2969, tgid 2969 (kworker/u4:9), ts 71102737145, free_ts 71028703403
 set_page_owner include/linux/page_owner.h:31 [inline]
 post_alloc_hook+0x1cd/0x210 mm/page_alloc.c:1554
 prep_new_page mm/page_alloc.c:1561 [inline]
 get_page_from_freelist+0x195c/0x19f0 mm/page_alloc.c:3191
 __alloc_pages+0x1e3/0x460 mm/page_alloc.c:4457
 alloc_slab_page+0x5d/0x170 mm/slub.c:1881
 allocate_slab mm/slub.c:2028 [inline]
 new_slab+0x87/0x2e0 mm/slub.c:2081
 ___slab_alloc+0xc6d/0x1300 mm/slub.c:3253
 __slab_alloc mm/slub.c:3339 [inline]
 __slab_alloc_node mm/slub.c:3392 [inline]
 slab_alloc_node mm/slub.c:3485 [inline]
 __kmem_cache_alloc_node+0x1a2/0x260 mm/slub.c:3534
 __do_kmalloc_node mm/slab_common.c:1006 [inline]
 __kmalloc_node_track_caller+0xa2/0x230 mm/slab_common.c:1027
 kmalloc_reserve+0x117/0x260 net/core/skbuff.c:581
 __alloc_skb+0x138/0x2c0 net/core/skbuff.c:650
 alloc_skb include/linux/skbuff.h:1284 [inline]
 nlmsg_new include/net/netlink.h:1010 [inline]
 rtmsg_ifinfo_build_skb+0x8c/0x260 net/core/rtnetlink.c:4063
 unregister_netdevice_many_notify+0xfd9/0x1810 net/core/dev.c:11090
 ip_tunnel_delete_nets+0x31c/0x360 net/ipv4/ip_tunnel.c:1157
 ops_exit_list net/core/net_namespace.c:178 [inline]
 cleanup_net+0x77f/0xb90 net/core/net_namespace.c:652
 process_one_work kernel/workqueue.c:2634 [inline]
 process_scheduled_works+0xa45/0x15b0 kernel/workqueue.c:2711
 worker_thread+0xa55/0xfc0 kernel/workqueue.c:2792
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1154 [inline]
 free_unref_page_prepare+0x7ce/0x8e0 mm/page_alloc.c:2336
 free_unref_page+0x32/0x2e0 mm/page_alloc.c:2429
 __slab_free+0x35e/0x410 mm/slub.c:3736
 qlink_free mm/kasan/quarantine.c:166 [inline]
 qlist_free_all+0x75/0xe0 mm/kasan/quarantine.c:185
 kasan_quarantine_reduce+0x143/0x160 mm/kasan/quarantine.c:292
 __kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:305
 kasan_slab_alloc include/linux/kasan.h:188 [inline]
 slab_post_alloc_hook+0x6e/0x4d0 mm/slab.h:767
 slab_alloc_node mm/slub.c:3495 [inline]
 kmem_cache_alloc_node+0x150/0x330 mm/slub.c:3540
 __alloc_skb+0x108/0x2c0 net/core/skbuff.c:640
 alloc_skb include/linux/skbuff.h:1284 [inline]
 nlmsg_new include/net/netlink.h:1010 [inline]
 mpls_netconf_notify_devconf+0x46/0xf0 net/mpls/af_mpls.c:1189
 mpls_dev_notify+0x533/0x7a0 net/mpls/af_mpls.c:1643
 notifier_call_chain+0x197/0x390 kernel/notifier.c:93
 call_netdevice_notifiers_extack net/core/dev.c:2064 [inline]
 call_netdevice_notifiers net/core/dev.c:2078 [inline]
 unregister_netdevice_many_notify+0xf36/0x1810 net/core/dev.c:11086
 ip_tunnel_delete_nets+0x31c/0x360 net/ipv4/ip_tunnel.c:1157
 ops_exit_list net/core/net_namespace.c:178 [inline]
 cleanup_net+0x77f/0xb90 net/core/net_namespace.c:652
 process_one_work kernel/workqueue.c:2634 [inline]
 process_scheduled_works+0xa45/0x15b0 kernel/workqueue.c:2711

Memory state around the buggy address:
 ffff88801c6bc380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88801c6bc400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88801c6bc480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff88801c6bc500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88801c6bc580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Crashes (23):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/11/01 19:35 linux-6.6.y e5bbb12db2c7 2c50b6a9 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Read in l2cap_connect_cfm
2026/06/18 01:44 linux-6.6.y 924b4a879cbb b62b3ded .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Read in l2cap_connect_cfm
2026/06/11 05:15 linux-6.6.y 924b4a879cbb b754d2d8 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Read in l2cap_connect_cfm
2026/06/10 14:42 linux-6.6.y 924b4a879cbb f79bac11 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Read in l2cap_connect_cfm
2026/05/29 16:03 linux-6.6.y 0a40c6fbd105 6b4a8443 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Read in l2cap_connect_cfm
2026/05/17 00:25 linux-6.6.y 4d922539ad7d de5aae85 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Read in l2cap_connect_cfm
2026/05/07 15:43 linux-6.6.y 258cf62a6dfd cbf9e0fc .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Read in l2cap_connect_cfm
2026/05/02 20:04 linux-6.6.y 258cf62a6dfd a0d91488 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Read in l2cap_connect_cfm
2026/03/24 04:46 linux-6.6.y 4fc00fe35d46 baf8bf12 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Read in l2cap_connect_cfm
2026/03/21 16:01 linux-6.6.y 4fc00fe35d46 5b92003d .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Read in l2cap_connect_cfm
2026/03/18 19:34 linux-6.6.y 4fc00fe35d46 0199f9a1 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Read in l2cap_connect_cfm
2026/03/06 20:25 linux-6.6.y 4fc00fe35d46 41d8037d .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Read in l2cap_connect_cfm
2026/02/17 17:58 linux-6.6.y 56865d9b7074 06ec4f7b .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Read in l2cap_connect_cfm
2026/02/04 00:57 linux-6.6.y 2cf6f68313dc 42b01fab .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Read in l2cap_connect_cfm
2026/01/25 03:14 linux-6.6.y cbb31f77b879 40acda8a .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Read in l2cap_connect_cfm
2026/01/21 11:09 linux-6.6.y cbb31f77b879 6f1aa2f9 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Read in l2cap_connect_cfm
2026/01/03 16:51 linux-6.6.y 5fa4793a2d2d d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Read in l2cap_connect_cfm
2025/11/07 13:55 linux-6.6.y 0a805b6ea8cd 4e1406b4 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Read in l2cap_connect_cfm
2025/11/01 17:23 linux-6.6.y e5bbb12db2c7 2c50b6a9 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Read in l2cap_connect_cfm
2025/10/23 19:41 linux-6.6.y 4a243110dc88 c0460fcd .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Read in l2cap_connect_cfm
2025/09/18 09:38 linux-6.6.y 60a9e718726f e2beed91 .config console log report syz / log [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Read in l2cap_connect_cfm
2025/09/18 08:10 linux-6.6.y 60a9e718726f e2beed91 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-use-after-free Read in l2cap_connect_cfm
2025/10/30 22:20 linux-6.6.y e5bbb12db2c7 2c50b6a9 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: wild-memory-access Read in l2cap_connect_cfm
* Struck through repros no longer work on HEAD.