KASAN: slab-use-after-free Read in l2cap_disconn_ind (3)

Status: upstream: reported on 2026/05/13 08:12
Subsystems: bluetooth
Labels: prio:high
[Documentation on labels]
Reported-by: syzbot+9c40ad7c6ed7165e46e8@syzkaller.appspotmail.com
Fix commit: Bluetooth: L2CAP: use proto_lock for l2cap_data to fix l2cap_disconn_ind
Patched on: [ci-upstream-linux-next-kasan-gce-root ci-upstream-net-kasan-gce], missing on: [ci-qemu-gce-upstream-auto ci-qemu-native-arm64-kvm ci-qemu-upstream ci-qemu-upstream-386 ci-qemu2-arm32 ci-qemu2-arm64 ci-qemu2-arm64-compat ci-qemu2-arm64-mte ci-qemu2-riscv64 ci-snapshot-upstream-root ci-upstream-bpf-kasan-gce ci-upstream-bpf-next-kasan-gce ci-upstream-gce-arm64 ci-upstream-gce-leak ci-upstream-kasan-badwrites-root ci-upstream-kasan-gce ci-upstream-kasan-gce-386 ci-upstream-kasan-gce-root ci-upstream-kasan-gce-selinux-root ci-upstream-kasan-gce-smack-root ci-upstream-kmsan-gce-386-root ci-upstream-kmsan-gce-root ci-upstream-net-this-kasan-gce ci-upstream-rust-kasan-gce ci2-upstream-fs ci2-upstream-kcsan-gce ci2-upstream-usb]
First crash: 90d, last: 11d
▶ ▼ ✨ AI Jobs (2)
ID Workflow Result Correct Bug Created Started Finished Revision
1b93e63d repro-c 💥 KASAN: slab-use-after-free Read in l2cap_disconn_ind (3) 2026/05/25 10:25 2026/05/25 10:43 2026/05/25 17:16 c69befb3
0eb3bda0 assessment-security DenialOfService: ✅ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ✅ RemoteTrigger: ✅ Unprivileged: ✅ UserNamespace: ✅ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ KASAN: slab-use-after-free Read in l2cap_disconn_ind (3) 2026/05/24 16:24 2026/05/24 16:24 2026/05/24 17:13 c69befb3
▶ ▼ Discussions (3)
Title Replies (including bot) Last reply
[PATCH 1/2] Bluetooth: L2CAP: use proto_lock for l2cap_data to fix l2cap_disconn_ind 3 (3) 2026/08/04 17:40
[PATCH] Bluetooth: L2CAP: Fix slab-use-after-free in l2cap_disconn_ind 1 (1) 2026/06/29 11:05
[syzbot] [bluetooth?] KASAN: slab-use-after-free Read in l2cap_disconn_ind (3) 0 (1) 2026/05/13 08:12
▶ ▼ Similar bugs (2)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KASAN: slab-use-after-free Read in l2cap_disconn_ind (2) bluetooth 19 6 272d 307d 0/29 auto-obsoleted due to no activity on 2026/02/16 10:02
upstream KASAN: slab-use-after-free Read in l2cap_disconn_ind bluetooth 19 2 552d 623d 0/29 auto-obsoleted due to no activity on 2025/05/12 10:49

Sample crash report:
==================================================================
BUG: KASAN: slab-use-after-free in l2cap_disconn_ind+0xd7/0xf0 net/bluetooth/l2cap_core.c:7586
Read of size 1 at addr ffff88807b5f5a78 by task kworker/u9:4/5631

CPU: 1 UID: 0 PID: 5631 Comm: kworker/u9:4 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
Workqueue: hci2 hci_conn_timeout
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0x13d/0x4b0 mm/kasan/report.c:482
 kasan_report+0xdf/0x1c0 mm/kasan/report.c:595
 l2cap_disconn_ind+0xd7/0xf0 net/bluetooth/l2cap_core.c:7586
 hci_proto_disconn_ind include/net/bluetooth/hci_core.h:2113 [inline]
 hci_conn_timeout+0x1dc/0x230 net/bluetooth/hci_conn.c:643
 process_one_work+0xa23/0x1940 kernel/workqueue.c:3322
 process_scheduled_works kernel/workqueue.c:3405 [inline]
 worker_thread+0x5ef/0xe50 kernel/workqueue.c:3486
 kthread+0x370/0x450 kernel/kthread.c:436
 ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>

Allocated by task 11153:
 kasan_save_stack+0x30/0x50 mm/kasan/common.c:57
 kasan_save_track+0x14/0x30 mm/kasan/common.c:78
 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
 __kasan_kmalloc+0xaa/0xb0 mm/kasan/common.c:415
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __kmalloc_cache_noprof+0x2e5/0x6c0 mm/slub.c:5489
 _kmalloc_noprof include/linux/slab.h:988 [inline]
 _kzalloc_noprof include/linux/slab.h:1309 [inline]
 l2cap_conn_add.part.0+0x60/0xb00 net/bluetooth/l2cap_core.c:7159
 l2cap_conn_add include/net/bluetooth/l2cap.h:840 [inline]
 l2cap_chan_connect+0x1435/0x1f90 net/bluetooth/l2cap_core.c:7350
 l2cap_sock_connect+0x37a/0x770 net/bluetooth/l2cap_sock.c:255
 kernel_connect+0x107/0x160 net/socket.c:3726
 rfcomm_session_create net/bluetooth/rfcomm/core.c:808 [inline]
 __rfcomm_dlc_open net/bluetooth/rfcomm/core.c:385 [inline]
 rfcomm_dlc_open+0x838/0xac0 net/bluetooth/rfcomm/core.c:428
 rfcomm_sock_connect+0x42c/0x690 net/bluetooth/rfcomm/sock.c:420
 __sys_connect_file+0x141/0x1a0 net/socket.c:2135
 __sys_connect+0x141/0x170 net/socket.c:2154
 __do_sys_connect net/socket.c:2160 [inline]
 __se_sys_connect net/socket.c:2157 [inline]
 __x64_sys_connect+0x72/0xb0 net/socket.c:2157
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 3205:
 kasan_save_stack+0x30/0x50 mm/kasan/common.c:57
 kasan_save_track+0x14/0x30 mm/kasan/common.c:78
 kasan_save_free_info+0x3b/0x70 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x5f/0x80 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2677 [inline]
 slab_free mm/slub.c:6377 [inline]
 kfree+0x22b/0x6c0 mm/slub.c:6692
 l2cap_conn_free net/bluetooth/l2cap_core.c:1846 [inline]
 kref_put include/linux/kref.h:65 [inline]
 l2cap_conn_put net/bluetooth/l2cap_core.c:1858 [inline]
 l2cap_chan_destroy net/bluetooth/l2cap_core.c:494 [inline]
 kref_put include/linux/kref.h:65 [inline]
 l2cap_chan_put+0x35a/0x3f0 net/bluetooth/l2cap_core.c:521
 l2cap_sock_release+0x1db/0x280 net/bluetooth/l2cap_sock.c:1495
 __sock_release net/socket.c:710 [inline]
 sock_release+0x91/0x1c0 net/socket.c:738
 rfcomm_session_del.isra.0+0x16b/0x250 net/bluetooth/rfcomm/core.c:718
 rfcomm_process_rx net/bluetooth/rfcomm/core.c:2002 [inline]
 rfcomm_process_sessions net/bluetooth/rfcomm/core.c:2087 [inline]
 rfcomm_run+0x6dc/0x5580 net/bluetooth/rfcomm/core.c:2175
 kthread+0x370/0x450 kernel/kthread.c:436
 ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

The buggy address belongs to the object at ffff88807b5f5800
 which belongs to the cache kmalloc-1k of size 1024
The buggy address is located 632 bytes inside of
 freed 1024-byte region [ffff88807b5f5800, ffff88807b5f5c00)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x7b5f0
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000040 ffff88813fe21dc0 dead000000000100 dead000000000122
raw: 0000000000000000 0000000800100010 00000000f5000000 0000000000000000
head: 00fff00000000040 ffff88813fe21dc0 dead000000000100 dead000000000122
head: 0000000000000000 0000000800100010 00000000f5000000 0000000000000000
head: 00fff00000000003 fffffffffffffe01 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000008
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0x1d2820(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC|__GFP_HARDWALL), pid 341, tgid 341 (kworker/u8:6), ts 742325943136, free_ts 742295273916
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0xfd/0x120 mm/page_alloc.c:1859
 prep_new_page mm/page_alloc.c:1867 [inline]
 get_page_from_freelist+0xf48/0x3530 mm/page_alloc.c:3946
 __alloc_frozen_pages_noprof+0x299/0x2dc0 mm/page_alloc.c:5304
 alloc_slab_page mm/slub.c:3266 [inline]
 allocate_slab mm/slub.c:3380 [inline]
 new_slab+0xa2/0x640 mm/slub.c:3426
 refill_objects+0xe3/0x410 mm/slub.c:7310
 refill_sheaf mm/slub.c:2804 [inline]
 __pcs_replace_empty_main+0x376/0x680 mm/slub.c:4675
 alloc_from_pcs mm/slub.c:4773 [inline]
 slab_alloc_node mm/slub.c:4905 [inline]
 __do_kmalloc_node mm/slub.c:5333 [inline]
 __kmalloc_noprof+0x66d/0x820 mm/slub.c:5359
 _kmalloc_noprof include/linux/slab.h:992 [inline]
 _kzalloc_noprof include/linux/slab.h:1309 [inline]
 ieee802_11_parse_elems_full+0x17c/0x3bc0 net/mac80211/parse.c:1073
 ieee802_11_parse_elems net/mac80211/ieee80211_i.h:2551 [inline]
 ieee80211_inform_bss+0x159/0x1170 net/mac80211/scan.c:79
 rdev_inform_bss net/wireless/rdev-ops.h:418 [inline]
 cfg80211_inform_single_bss_data+0x898/0x1dc0 net/wireless/scan.c:2382
 cfg80211_inform_bss_data+0x230/0x3b60 net/wireless/scan.c:3241
 cfg80211_inform_bss_frame_data+0x245/0x7c0 net/wireless/scan.c:3333
 ieee80211_bss_info_update+0x310/0xab0 net/mac80211/scan.c:230
 ieee80211_rx_bss_info net/mac80211/ibss.c:1063 [inline]
 ieee80211_rx_mgmt_probe_beacon net/mac80211/ibss.c:1544 [inline]
 ieee80211_ibss_rx_queued_mgmt+0xe04/0x1c70 net/mac80211/ibss.c:1571
 ieee80211_iface_process_skb net/mac80211/iface.c:1769 [inline]
 ieee80211_iface_work+0xa9a/0x1070 net/mac80211/iface.c:1823
 cfg80211_wiphy_work+0x2b7/0x550 net/wireless/core.c:538
page last free pid 9832 tgid 9832 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 __free_pages_prepare mm/page_alloc.c:1406 [inline]
 __free_frozen_pages+0x79f/0x1090 mm/page_alloc.c:2950
 qlink_free mm/kasan/quarantine.c:163 [inline]
 qlist_free_all+0x47/0xf0 mm/kasan/quarantine.c:179
 kasan_quarantine_reduce+0x1a0/0x1f0 mm/kasan/quarantine.c:286
 __kasan_slab_alloc+0x69/0x90 mm/kasan/common.c:350
 kasan_slab_alloc include/linux/kasan.h:253 [inline]
 slab_post_alloc_hook mm/slub.c:4584 [inline]
 slab_alloc_node mm/slub.c:4917 [inline]
 __do_kmalloc_node mm/slub.c:5333 [inline]
 __kvmalloc_node_noprof+0x2eb/0x970 mm/slub.c:6905
 xt_alloc_table_info+0x44/0xa0 net/netfilter/x_tables.c:1286
 do_replace net/ipv6/netfilter/ip6_tables.c:1141 [inline]
 do_ip6t_set_ctl+0x611/0xd00 net/ipv6/netfilter/ip6_tables.c:1643
 nf_setsockopt+0x8d/0xf0 net/netfilter/nf_sockopt.c:101
 ipv6_setsockopt+0x135/0x170 net/ipv6/ipv6_sockglue.c:970
 tcp_setsockopt+0xa7/0x100 net/ipv4/tcp.c:4179
 do_sock_setsockopt+0xf3/0x1d0 net/socket.c:2368
 __sys_setsockopt+0x195/0x220 net/socket.c:2393
 __do_sys_setsockopt net/socket.c:2399 [inline]
 __se_sys_setsockopt net/socket.c:2396 [inline]
 __x64_sys_setsockopt+0xbd/0x160 net/socket.c:2396
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff88807b5f5900: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88807b5f5980: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88807b5f5a00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                                ^
 ffff88807b5f5a80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88807b5f5b00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/07/27 17:02 upstream f5098b6bae76 4cb2b096 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-badwrites-root KASAN: slab-use-after-free Read in l2cap_disconn_ind
2026/05/10 03:16 upstream 1bfaee9d3351 29233ece .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-selinux-root KASAN: slab-use-after-free Read in l2cap_disconn_ind
* Struck through repros no longer work on HEAD.