[syzbot] [bluetooth?] KASAN: slab-use-after-free Read in l2cap_unregister_user

[syzbot] [bluetooth?] KASAN: slab-use-after-free Read in l2cap_unregister_user

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    90602c251cda Merge tag 'net-6.12-rc6' of git://git.kernel...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10076630580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=4340261e4e9f37fc
dashboard link: https://syzkaller.appspot.com/bug?extid=14b6d57fb728e27ce23c
compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15bd9340580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7feb34a89c2a/non_bootable_disk-90602c25.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/6a2daa3dcb25/vmlinux-90602c25.xz
kernel image: https://storage.googleapis.com/syzbot-assets/4488ee6eec29/bzImage-90602c25.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+14b6d57fb728e27ce23c@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-use-after-free in __mutex_waiter_is_first kernel/locking/mutex.c:197 [inline]
BUG: KASAN: slab-use-after-free in __mutex_lock_common kernel/locking/mutex.c:686 [inline]
BUG: KASAN: slab-use-after-free in __mutex_lock+0x8e6/0x9c0 kernel/locking/mutex.c:752
Read of size 8 at addr ffff888021760060 by task khidpd_0007fff9/6116

CPU: 3 UID: 0 PID: 6116 Comm: khidpd_0007fff9 Not tainted 6.12.0-rc5-syzkaller-00161-g90602c251cda #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:377 [inline]
 print_report+0xc3/0x620 mm/kasan/report.c:488
 kasan_report+0xd9/0x110 mm/kasan/report.c:601
 __mutex_waiter_is_first kernel/locking/mutex.c:197 [inline]
 __mutex_lock_common kernel/locking/mutex.c:686 [inline]
 __mutex_lock+0x8e6/0x9c0 kernel/locking/mutex.c:752
 l2cap_unregister_user+0x71/0x240 net/bluetooth/l2cap_core.c:1726
 hidp_session_thread+0x462/0x650 net/bluetooth/hidp/core.c:1304
 kthread+0x2c1/0x3a0 kernel/kthread.c:389
 ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>

Allocated by task 6062:
 kasan_save_stack+0x33/0x60 mm/kasan/common.c:47
 kasan_save_track+0x14/0x30 mm/kasan/common.c:68
 poison_kmalloc_redzone mm/kasan/common.c:377 [inline]
 __kasan_kmalloc+0xaa/0xb0 mm/kasan/common.c:394
 kasan_kmalloc include/linux/kasan.h:257 [inline]
 __do_kmalloc_node mm/slub.c:4264 [inline]
 __kmalloc_noprof+0x1e8/0x400 mm/slub.c:4276
 kmalloc_noprof include/linux/slab.h:882 [inline]
 kzalloc_noprof include/linux/slab.h:1014 [inline]
 hci_alloc_dev_priv+0x1d/0x2820 net/bluetooth/hci_core.c:2440
 hci_alloc_dev include/net/bluetooth/hci_core.h:1621 [inline]
 __vhci_create_device+0xef/0x7d0 drivers/bluetooth/hci_vhci.c:399
 vhci_create_device drivers/bluetooth/hci_vhci.c:470 [inline]
 vhci_get_user drivers/bluetooth/hci_vhci.c:527 [inline]
 vhci_write+0x2c3/0x470 drivers/bluetooth/hci_vhci.c:607
 new_sync_write fs/read_write.c:590 [inline]
 vfs_write+0x5ae/0x1150 fs/read_write.c:683
 ksys_write+0x12f/0x260 fs/read_write.c:736
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 6062:
 kasan_save_stack+0x33/0x60 mm/kasan/common.c:47
 kasan_save_track+0x14/0x30 mm/kasan/common.c:68
 kasan_save_free_info+0x3b/0x60 mm/kasan/generic.c:579
 poison_slab_object mm/kasan/common.c:247 [inline]
 __kasan_slab_free+0x51/0x70 mm/kasan/common.c:264
 kasan_slab_free include/linux/kasan.h:230 [inline]
 slab_free_hook mm/slub.c:2342 [inline]
 slab_free mm/slub.c:4579 [inline]
 kfree+0x14f/0x4b0 mm/slub.c:4727
 hci_release_dev+0x4d9/0x600 net/bluetooth/hci_core.c:2759
 bt_host_release+0x6a/0xb0 net/bluetooth/hci_sysfs.c:94
 device_release+0xa1/0x240 drivers/base/core.c:2575
 kobject_cleanup lib/kobject.c:689 [inline]
 kobject_release lib/kobject.c:720 [inline]
 kref_put include/linux/kref.h:65 [inline]
 kobject_put+0x1e4/0x5a0 lib/kobject.c:737
 put_device+0x1f/0x30 drivers/base/core.c:3783
 vhci_release+0x81/0xf0 drivers/bluetooth/hci_vhci.c:665
 __fput+0x3f6/0xb60 fs/file_table.c:431
 task_work_run+0x14e/0x250 kernel/task_work.c:239
 exit_task_work include/linux/task_work.h:43 [inline]
 do_exit+0xadd/0x2d70 kernel/exit.c:939
 do_group_exit+0xd3/0x2a0 kernel/exit.c:1088
 __do_sys_exit_group kernel/exit.c:1099 [inline]
 __se_sys_exit_group kernel/exit.c:1097 [inline]
 __x64_sys_exit_group+0x3e/0x50 kernel/exit.c:1097
 x64_sys_call+0x14a9/0x16a0 arch/x86/include/generated/asm/syscalls_64.h:232
 do_syscall_x64 arch/x86/entry/common.c:52 [inline]
 do_syscall_64+0xcd/0x250 arch/x86/entry/common.c:83
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Last potentially related work creation:
 kasan_save_stack+0x33/0x60 mm/kasan/common.c:47
 __kasan_record_aux_stack+0xba/0xd0 mm/kasan/generic.c:541
 insert_work+0x36/0x230 kernel/workqueue.c:2183
 __queue_work+0x3f8/0x1080 kernel/workqueue.c:2343
 queue_work_on+0x11a/0x140 kernel/workqueue.c:2390
 process_one_work+0x9c5/0x1ba0 kernel/workqueue.c:3229
 process_scheduled_works kernel/workqueue.c:3310 [inline]
 worker_thread+0x6c8/0xf00 kernel/workqueue.c:3391
 kthread+0x2c1/0x3a0 kernel/kthread.c:389
 ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

Second to last potentially related work creation:
 kasan_save_stack+0x33/0x60 mm/kasan/common.c:47
 __kasan_record_aux_stack+0xba/0xd0 mm/kasan/generic.c:541
 insert_work+0x36/0x230 kernel/workqueue.c:2183
 __queue_work+0x97e/0x1080 kernel/workqueue.c:2339
 call_timer_fn+0x1a0/0x610 kernel/time/timer.c:1794
 expire_timers kernel/time/timer.c:1840 [inline]
 __run_timers+0x56a/0x930 kernel/time/timer.c:2419
 __run_timer_base kernel/time/timer.c:2430 [inline]
 __run_timer_base kernel/time/timer.c:2423 [inline]
 run_timer_base+0x111/0x190 kernel/time/timer.c:2439
 run_timer_softirq+0x1a/0x40 kernel/time/timer.c:2449
 handle_softirqs+0x213/0x8f0 kernel/softirq.c:554
 __do_softirq kernel/softirq.c:588 [inline]
 invoke_softirq kernel/softirq.c:428 [inline]
 __irq_exit_rcu kernel/softirq.c:637 [inline]
 irq_exit_rcu+0xbb/0x120 kernel/softirq.c:649
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1049 [inline]
 sysvec_apic_timer_interrupt+0xa4/0xc0 arch/x86/kernel/apic/apic.c:1049
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702

The buggy address belongs to the object at ffff888021760000
 which belongs to the cache kmalloc-8k of size 8192
The buggy address is located 96 bytes inside of
 freed 8192-byte region [ffff888021760000, ffff888021762000)

The buggy address belongs to the physical page:
page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x21760
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 ffff88801b043180 dead000000000100 dead000000000122
raw: 0000000000000000 0000000000020002 00000001f5000000 0000000000000000
head: 00fff00000000040 ffff88801b043180 dead000000000100 dead000000000122
head: 0000000000000000 0000000000020002 00000001f5000000 0000000000000000
head: 00fff00000000003 ffffea000085d801 ffffffffffffffff 0000000000000000
head: 0000000000000008 0000000000000000 00000000ffffffff 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 0xd2040(__GFP_IO|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 5654, tgid 5654 (sh), ts 21301582122, free_ts 21285906849
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x2d1/0x350 mm/page_alloc.c:1537
 prep_new_page mm/page_alloc.c:1545 [inline]
 get_page_from_freelist+0x101e/0x3070 mm/page_alloc.c:3457
 __alloc_pages_noprof+0x223/0x25a0 mm/page_alloc.c:4733
 alloc_pages_mpol_noprof+0x2c9/0x610 mm/mempolicy.c:2265
 alloc_slab_page mm/slub.c:2412 [inline]
 allocate_slab mm/slub.c:2578 [inline]
 new_slab+0x2ba/0x3f0 mm/slub.c:2631
 ___slab_alloc+0xdac/0x1880 mm/slub.c:3818
 __slab_alloc.constprop.0+0x56/0xb0 mm/slub.c:3908
 __slab_alloc_node mm/slub.c:3961 [inline]
 slab_alloc_node mm/slub.c:4122 [inline]
 __kmalloc_cache_noprof+0x2b4/0x300 mm/slub.c:4290
 kmalloc_noprof include/linux/slab.h:878 [inline]
 kzalloc_noprof include/linux/slab.h:1014 [inline]
 tomoyo_print_bprm security/tomoyo/audit.c:26 [inline]
 tomoyo_init_log+0xcb3/0x2170 security/tomoyo/audit.c:264
 tomoyo_supervisor+0x30c/0xea0 security/tomoyo/common.c:2089
 tomoyo_audit_path_log security/tomoyo/file.c:168 [inline]
 tomoyo_execute_permission+0x38e/0x4b0 security/tomoyo/file.c:619
 tomoyo_find_next_domain+0x361/0x2070 security/tomoyo/domain.c:755
 tomoyo_bprm_check_security security/tomoyo/tomoyo.c:102 [inline]
 tomoyo_bprm_check_security+0x12b/0x1d0 security/tomoyo/tomoyo.c:92
 security_bprm_check+0x1b9/0x1e0 security/security.c:1297
 search_binary_handler fs/exec.c:1740 [inline]
 exec_binprm fs/exec.c:1794 [inline]
 bprm_execve fs/exec.c:1845 [inline]
 bprm_execve+0x642/0x1960 fs/exec.c:1821
 do_execveat_common.isra.0+0x4f1/0x630 fs/exec.c:1952
page last free pid 5653 tgid 5653 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1108 [inline]
 free_unref_page+0x5f4/0xdc0 mm/page_alloc.c:2638
 __put_partials+0x14c/0x170 mm/slub.c:3145
 qlink_free mm/kasan/quarantine.c:163 [inline]
 qlist_free_all+0x4e/0x120 mm/kasan/quarantine.c:179
 kasan_quarantine_reduce+0x192/0x1e0 mm/kasan/quarantine.c:286
 __kasan_slab_alloc+0x69/0x90 mm/kasan/common.c:329
 kasan_slab_alloc include/linux/kasan.h:247 [inline]
 slab_post_alloc_hook mm/slub.c:4085 [inline]
 slab_alloc_node mm/slub.c:4134 [inline]
 __kmalloc_cache_noprof+0x11e/0x300 mm/slub.c:4290
 kmalloc_noprof include/linux/slab.h:878 [inline]
 tomoyo_print_header security/tomoyo/audit.c:156 [inline]
 tomoyo_init_log+0x195/0x2170 security/tomoyo/audit.c:255
 tomoyo_supervisor+0x30c/0xea0 security/tomoyo/common.c:2089
 tomoyo_audit_path_log security/tomoyo/file.c:168 [inline]
 tomoyo_path_permission security/tomoyo/file.c:587 [inline]
 tomoyo_path_permission+0x270/0x3b0 security/tomoyo/file.c:573
 tomoyo_path_perm+0x35e/0x450 security/tomoyo/file.c:838
 security_inode_getattr+0x116/0x290 security/security.c:2373
 vfs_getattr+0x36/0xb0 fs/stat.c:204
 vfs_statx_path+0x36/0x390 fs/stat.c:251
 vfs_statx+0x145/0x1e0 fs/stat.c:315
 vfs_fstatat+0x9f/0x160 fs/stat.c:341
 __do_sys_newfstatat+0xa2/0x130 fs/stat.c:505

Memory state around the buggy address:
 ffff88802175ff00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88802175ff80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888021760000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                       ^
 ffff888021760080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888021760100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
This report is generated by a bot. It may contain errors.
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If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to overwrite report's subsystems, reply with:
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#syz undup

Re: [syzbot] [bluetooth?] KASAN: slab-use-after-free Read in l2cap_unregister_user

[Hillf Danton]

On Fri, 01 Nov 2024 11:29:21 -0700
> syzbot found the following issue on:
> 
> HEAD commit:    90602c251cda Merge tag 'net-6.12-rc6' of git://git.kernel...
> git tree:       upstream
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15bd9340580000

#syz test

--- l/net/bluetooth/hidp/core.c
+++ y/net/bluetooth/hidp/core.c
@@ -1302,6 +1302,7 @@ static int hidp_session_thread(void *arg
 	 * delete the session.
 	 */
 	l2cap_unregister_user(session->conn, &session->user);
+	hci_dev_put(session->conn->hcon->hdev);
 	hidp_session_put(session);
 
 	module_put_and_kthread_exit(0);
@@ -1378,6 +1379,7 @@ int hidp_connection_add(const struct hid
 	ret = l2cap_register_user(conn, &session->user);
 	if (ret)
 		goto out_session;
+	hci_dev_hold(conn->hcon->hdev);
 
 	ret = 0;
 
@@ -1405,8 +1407,10 @@ int hidp_connection_del(struct hidp_conn
 				       HIDP_TRANS_HID_CONTROL |
 				         HIDP_CTRL_VIRTUAL_CABLE_UNPLUG,
 				       NULL, 0);
-	else
+	else {
 		l2cap_unregister_user(session->conn, &session->user);
+		hci_dev_put(session->conn->hcon->hdev);
+	}
 
 	hidp_session_put(session);
 
--

Re: [syzbot] [bluetooth?] KASAN: slab-use-after-free Read in l2cap_unregister_user

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+14b6d57fb728e27ce23c@syzkaller.appspotmail.com
Tested-by: syzbot+14b6d57fb728e27ce23c@syzkaller.appspotmail.com

Tested on:

commit:         c4264568 Merge tag 'acpi-6.12-rc6' of git://git.kernel..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=101af2a7980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=4340261e4e9f37fc
dashboard link: https://syzkaller.appspot.com/bug?extid=14b6d57fb728e27ce23c
compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=142ce187980000

Note: testing is done by a robot and is best-effort only.

Re: [syzbot] [bluetooth?] KASAN: slab-use-after-free Read in l2cap_unregister_user

[syzbot]

syzbot has bisected this issue to:

commit c8992cffbe7411c6da4c4416d5eecfc6b78e0fec
Author: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Date:   Wed Dec 1 18:55:05 2021 +0000

    Bluetooth: hci_event: Use of a function table to handle Command Complete

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=14d538c4580000
start commit:   30b981796b94 selftests: drv-net: test empty queue and NAPI..
git tree:       net
final oops:     https://syzkaller.appspot.com/x/report.txt?x=16d538c4580000
console output: https://syzkaller.appspot.com/x/log.txt?x=12d538c4580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=6a2b862bf4a5409f
dashboard link: https://syzkaller.appspot.com/bug?extid=14b6d57fb728e27ce23c
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=12050adf980000

Reported-by: syzbot+14b6d57fb728e27ce23c@syzkaller.appspotmail.com
Fixes: c8992cffbe74 ("Bluetooth: hci_event: Use of a function table to handle Command Complete")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection

Re: [syzbot] [bluetooth?] KASAN: slab-use-after-free Read in l2cap_unregister_user

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit:    8f5ae30d69d7 Linux 6.17-rc1
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
console output: https://syzkaller.appspot.com/x/log.txt?x=15494c34580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=8c5ac3d8b8abfcb
dashboard link: https://syzkaller.appspot.com/bug?extid=14b6d57fb728e27ce23c
compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
userspace arch: arm64
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1428caf0580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11da19a2580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/18a2e4bd0c4a/disk-8f5ae30d.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/3b5395881b25/vmlinux-8f5ae30d.xz
kernel image: https://storage.googleapis.com/syzbot-assets/e875f4e3b7ff/Image-8f5ae30d.gz.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/cdc3889e34d0/mount_4.gz
  fsck result: OK (log: https://syzkaller.appspot.com/x/fsck.log?x=1412a842580000)

The issue was bisected to:

commit c8992cffbe7411c6da4c4416d5eecfc6b78e0fec
Author: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
Date:   Wed Dec 1 18:55:05 2021 +0000

    Bluetooth: hci_event: Use of a function table to handle Command Complete

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=14d538c4580000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=16d538c4580000
console output: https://syzkaller.appspot.com/x/log.txt?x=12d538c4580000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+14b6d57fb728e27ce23c@syzkaller.appspotmail.com
Fixes: c8992cffbe74 ("Bluetooth: hci_event: Use of a function table to handle Command Complete")

==================================================================
BUG: KASAN: slab-use-after-free in __mutex_waiter_is_first kernel/locking/mutex.c:183 [inline]
BUG: KASAN: slab-use-after-free in __mutex_lock_common+0xcb4/0x24ac kernel/locking/mutex.c:678
Read of size 8 at addr ffff0000c99f80a0 by task khidpd_05c25886/6940

CPU: 0 UID: 0 PID: 6940 Comm: khidpd_05c25886 Not tainted 6.17.0-rc1-syzkaller-g8f5ae30d69d7 #0 PREEMPT 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/18/2025
Call trace:
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:499 (C)
 __dump_stack+0x30/0x40 lib/dump_stack.c:94
 dump_stack_lvl+0xd8/0x12c lib/dump_stack.c:120
 print_address_description+0xa8/0x238 mm/kasan/report.c:378
 print_report+0x68/0x84 mm/kasan/report.c:482
 kasan_report+0xb0/0x110 mm/kasan/report.c:595
 __asan_report_load8_noabort+0x20/0x2c mm/kasan/report_generic.c:381
 __mutex_waiter_is_first kernel/locking/mutex.c:183 [inline]
 __mutex_lock_common+0xcb4/0x24ac kernel/locking/mutex.c:678
 __mutex_lock kernel/locking/mutex.c:760 [inline]
 mutex_lock_nested+0x2c/0x38 kernel/locking/mutex.c:812
 l2cap_unregister_user+0x74/0x190 net/bluetooth/l2cap_core.c:1728
 hidp_session_thread+0x3d0/0x46c net/bluetooth/hidp/core.c:1304
 kthread+0x5fc/0x75c kernel/kthread.c:463
 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:844

Allocated by task 6767:
 kasan_save_stack mm/kasan/common.c:47 [inline]
 kasan_save_track+0x40/0x78 mm/kasan/common.c:68
 kasan_save_alloc_info+0x44/0x54 mm/kasan/generic.c:562
 poison_kmalloc_redzone mm/kasan/common.c:388 [inline]
 __kasan_kmalloc+0x9c/0xb4 mm/kasan/common.c:405
 kasan_kmalloc include/linux/kasan.h:260 [inline]
 __do_kmalloc_node mm/slub.c:4365 [inline]
 __kmalloc_noprof+0x2fc/0x4c8 mm/slub.c:4377
 kmalloc_noprof include/linux/slab.h:909 [inline]
 kzalloc_noprof include/linux/slab.h:1039 [inline]
 hci_alloc_dev_priv+0x2c/0x1b84 net/bluetooth/hci_core.c:2448
 hci_alloc_dev include/net/bluetooth/hci_core.h:1706 [inline]
 __vhci_create_device drivers/bluetooth/hci_vhci.c:399 [inline]
 vhci_create_device+0x108/0x6d4 drivers/bluetooth/hci_vhci.c:471
 vhci_get_user drivers/bluetooth/hci_vhci.c:528 [inline]
 vhci_write+0x314/0x3d4 drivers/bluetooth/hci_vhci.c:608
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x540/0xa3c fs/read_write.c:686
 ksys_write+0x120/0x210 fs/read_write.c:738
 __do_sys_write fs/read_write.c:749 [inline]
 __se_sys_write fs/read_write.c:746 [inline]
 __arm64_sys_write+0x7c/0x90 fs/read_write.c:746
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall+0x98/0x2b8 arch/arm64/kernel/syscall.c:49
 el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:132
 do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
 el0_svc+0x58/0x180 arch/arm64/kernel/entry-common.c:879
 el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:898
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596

Freed by task 6984:
 kasan_save_stack mm/kasan/common.c:47 [inline]
 kasan_save_track+0x40/0x78 mm/kasan/common.c:68
 kasan_save_free_info+0x58/0x70 mm/kasan/generic.c:576
 poison_slab_object mm/kasan/common.c:243 [inline]
 __kasan_slab_free+0x74/0x98 mm/kasan/common.c:275
 kasan_slab_free include/linux/kasan.h:233 [inline]
 slab_free_hook mm/slub.c:2417 [inline]
 slab_free mm/slub.c:4680 [inline]
 kfree+0x17c/0x474 mm/slub.c:4879
 hci_release_dev+0xf48/0x1060 net/bluetooth/hci_core.c:2776
 bt_host_release+0x70/0x8c net/bluetooth/hci_sysfs.c:87
 device_release+0x8c/0x1ac drivers/base/core.c:-1
 kobject_cleanup lib/kobject.c:689 [inline]
 kobject_release lib/kobject.c:720 [inline]
 kref_put include/linux/kref.h:65 [inline]
 kobject_put+0x2b0/0x438 lib/kobject.c:737
 put_device+0x28/0x40 drivers/base/core.c:3797
 hci_free_dev+0x24/0x34 net/bluetooth/hci_core.c:2579
 vhci_release+0x84/0xd0 drivers/bluetooth/hci_vhci.c:666
 __fput+0x340/0x75c fs/file_table.c:468
 ____fput+0x20/0x58 fs/file_table.c:496
 task_work_run+0x1dc/0x260 kernel/task_work.c:227
 exit_task_work include/linux/task_work.h:40 [inline]
 do_exit+0x524/0x1a14 kernel/exit.c:961
 do_group_exit+0x194/0x22c kernel/exit.c:1102
 get_signal+0x11dc/0x12f8 kernel/signal.c:3034
 do_signal+0x274/0x4434 arch/arm64/kernel/signal.c:1618
 do_notify_resume+0xb0/0x1f4 arch/arm64/kernel/entry-common.c:152
 exit_to_user_mode_prepare arch/arm64/kernel/entry-common.c:173 [inline]
 exit_to_user_mode arch/arm64/kernel/entry-common.c:182 [inline]
 el0_svc+0xb8/0x180 arch/arm64/kernel/entry-common.c:880
 el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:898
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596

Last potentially related work creation:
 kasan_save_stack+0x40/0x6c mm/kasan/common.c:47
 kasan_record_aux_stack+0xb0/0xc8 mm/kasan/generic.c:548
 insert_work+0x54/0x2cc kernel/workqueue.c:2184
 __queue_work+0xc88/0x1210 kernel/workqueue.c:2343
 queue_work_on+0xdc/0x18c kernel/workqueue.c:2390
 queue_work include/linux/workqueue.h:669 [inline]
 hci_cmd_timeout+0x178/0x1c8 net/bluetooth/hci_core.c:1480
 process_one_work+0x7e8/0x155c kernel/workqueue.c:3236
 process_scheduled_works kernel/workqueue.c:3319 [inline]
 worker_thread+0x958/0xed8 kernel/workqueue.c:3400
 kthread+0x5fc/0x75c kernel/kthread.c:463
 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:844

Second to last potentially related work creation:
 kasan_save_stack+0x40/0x6c mm/kasan/common.c:47
 kasan_record_aux_stack+0xb0/0xc8 mm/kasan/generic.c:548
 insert_work+0x54/0x2cc kernel/workqueue.c:2184
 __queue_work+0xdb0/0x1210 kernel/workqueue.c:2339
 delayed_work_timer_fn+0x74/0x90 kernel/workqueue.c:2485
 call_timer_fn+0x1b4/0x818 kernel/time/timer.c:1747
 expire_timers kernel/time/timer.c:1793 [inline]
 __run_timers kernel/time/timer.c:2372 [inline]
 __run_timer_base+0x54c/0x76c kernel/time/timer.c:2384
 run_timer_base kernel/time/timer.c:2393 [inline]
 run_timer_softirq+0xcc/0x194 kernel/time/timer.c:2403
 handle_softirqs+0x328/0xc88 kernel/softirq.c:579
 __do_softirq+0x14/0x20 kernel/softirq.c:613

The buggy address belongs to the object at ffff0000c99f8000
 which belongs to the cache kmalloc-8k of size 8192
The buggy address is located 160 bytes inside of
 freed 8192-byte region [ffff0000c99f8000, ffff0000c99fa000)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1099f8
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
anon flags: 0x5ffc00000000040(head|node=0|zone=2|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 05ffc00000000040 ffff0000c0002280 fffffdffc374ca00 0000000000000005
raw: 0000000000000000 0000000000020002 00000000f5000000 0000000000000000
head: 05ffc00000000040 ffff0000c0002280 fffffdffc374ca00 0000000000000005
head: 0000000000000000 0000000000020002 00000000f5000000 0000000000000000
head: 05ffc00000000003 fffffdffc3267e01 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000008
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff0000c99f7f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff0000c99f8000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff0000c99f8080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                               ^
 ffff0000c99f8100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff0000c99f8180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


---
If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

Re: [syzbot] [bluetooth?] KASAN: slab-use-after-free Read in l2cap_unregister_user

[Hillf Danton]

> Date: Tue, 12 Aug 2025 09:31:35 -0700	[thread overview]
> syzbot has found a reproducer for the following issue on:
> 
> HEAD commit:    8f5ae30d69d7 Linux 6.17-rc1
> git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
> console output: https://syzkaller.appspot.com/x/log.txt?x=15494c34580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=8c5ac3d8b8abfcb
> dashboard link: https://syzkaller.appspot.com/bug?extid=14b6d57fb728e27ce23c
> userspace arch: arm64
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=1428caf0580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=11da19a2580000

#syz test

--- x/net/bluetooth/l2cap_core.c
+++ y/net/bluetooth/l2cap_core.c
@@ -1714,6 +1714,7 @@ int l2cap_register_user(struct l2cap_con
 
 	list_add(&user->list, &conn->users);
 	ret = 0;
+	hci_dev_hold(hdev);
 
 out_unlock:
 	hci_dev_unlock(hdev);
@@ -1735,6 +1736,7 @@ void l2cap_unregister_user(struct l2cap_
 
 out_unlock:
 	hci_dev_unlock(hdev);
+	hci_dev_put(hdev);
 }
 EXPORT_SYMBOL(l2cap_unregister_user);
 
--

Re: [syzbot] [bluetooth?] KASAN: slab-use-after-free Read in l2cap_unregister_user

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+14b6d57fb728e27ce23c@syzkaller.appspotmail.com
Tested-by: syzbot+14b6d57fb728e27ce23c@syzkaller.appspotmail.com

Tested on:

commit:         8f5ae30d Linux 6.17-rc1
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
console output: https://syzkaller.appspot.com/x/log.txt?x=16786842580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=8c5ac3d8b8abfcb
dashboard link: https://syzkaller.appspot.com/bug?extid=14b6d57fb728e27ce23c
compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
userspace arch: arm64
patch:          https://syzkaller.appspot.com/x/patch.diff?x=17f5caf0580000

Note: testing is done by a robot and is best-effort only.

Re: [syzbot] [bluetooth?] KASAN: slab-use-after-free Read in l2cap_unregister_user

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
KASAN: slab-use-after-free Read in l2cap_unregister_user

==================================================================
BUG: KASAN: slab-use-after-free in __mutex_waiter_is_first kernel/locking/mutex.c:183 [inline]
BUG: KASAN: slab-use-after-free in __mutex_lock_common+0xd18/0x2678 kernel/locking/mutex.c:678
Read of size 8 at addr ffff0000d69a80a0 by task khidpd_05c25886/7548

CPU: 1 UID: 0 PID: 7548 Comm: khidpd_05c25886 Not tainted syzkaller #0 PREEMPT 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/03/2025
Call trace:
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:499 (C)
 __dump_stack+0x30/0x40 lib/dump_stack.c:94
 dump_stack_lvl+0xd8/0x12c lib/dump_stack.c:120
 print_address_description+0xa8/0x238 mm/kasan/report.c:378
 print_report+0x68/0x84 mm/kasan/report.c:482
 kasan_report+0xb0/0x110 mm/kasan/report.c:595
 __asan_report_load8_noabort+0x20/0x2c mm/kasan/report_generic.c:381
 __mutex_waiter_is_first kernel/locking/mutex.c:183 [inline]
 __mutex_lock_common+0xd18/0x2678 kernel/locking/mutex.c:678
 __mutex_lock kernel/locking/mutex.c:760 [inline]
 mutex_lock_nested+0x2c/0x38 kernel/locking/mutex.c:812
 l2cap_unregister_user+0x74/0x190 net/bluetooth/l2cap_core.c:1728
 hidp_session_thread+0x3d0/0x46c net/bluetooth/hidp/core.c:1304
 kthread+0x5fc/0x75c kernel/kthread.c:463
 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:844

Allocated by task 7442:
 kasan_save_stack mm/kasan/common.c:56 [inline]
 kasan_save_track+0x40/0x78 mm/kasan/common.c:77
 kasan_save_alloc_info+0x44/0x54 mm/kasan/generic.c:573
 poison_kmalloc_redzone mm/kasan/common.c:400 [inline]
 __kasan_kmalloc+0x9c/0xb4 mm/kasan/common.c:417
 kasan_kmalloc include/linux/kasan.h:262 [inline]
 __do_kmalloc_node mm/slub.c:5642 [inline]
 __kmalloc_noprof+0x3fc/0x728 mm/slub.c:5654
 kmalloc_noprof include/linux/slab.h:961 [inline]
 kzalloc_noprof include/linux/slab.h:1094 [inline]
 hci_alloc_dev_priv+0x2c/0x1b84 net/bluetooth/hci_core.c:2448
 hci_alloc_dev include/net/bluetooth/hci_core.h:1751 [inline]
 __vhci_create_device drivers/bluetooth/hci_vhci.c:421 [inline]
 vhci_create_device+0x108/0x638 drivers/bluetooth/hci_vhci.c:479
 vhci_get_user drivers/bluetooth/hci_vhci.c:536 [inline]
 vhci_write+0x314/0x3d4 drivers/bluetooth/hci_vhci.c:616
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x540/0xa3c fs/read_write.c:686
 ksys_write+0x120/0x210 fs/read_write.c:738
 __do_sys_write fs/read_write.c:749 [inline]
 __se_sys_write fs/read_write.c:746 [inline]
 __arm64_sys_write+0x7c/0x90 fs/read_write.c:746
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall+0x98/0x254 arch/arm64/kernel/syscall.c:49
 el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:132
 do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
 el0_svc+0x5c/0x254 arch/arm64/kernel/entry-common.c:746
 el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:765
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596

Freed by task 7595:
 kasan_save_stack mm/kasan/common.c:56 [inline]
 kasan_save_track+0x40/0x78 mm/kasan/common.c:77
 __kasan_save_free_info+0x58/0x70 mm/kasan/generic.c:587
 kasan_save_free_info mm/kasan/kasan.h:406 [inline]
 poison_slab_object mm/kasan/common.c:252 [inline]
 __kasan_slab_free+0x74/0xa4 mm/kasan/common.c:284
 kasan_slab_free include/linux/kasan.h:234 [inline]
 slab_free_hook mm/slub.c:2539 [inline]
 slab_free mm/slub.c:6630 [inline]
 kfree+0x184/0x600 mm/slub.c:6837
 hci_release_dev+0xf48/0x1060 net/bluetooth/hci_core.c:2776
 bt_host_release+0x70/0x8c net/bluetooth/hci_sysfs.c:87
 device_release+0x8c/0x1ac drivers/base/core.c:-1
 kobject_cleanup lib/kobject.c:689 [inline]
 kobject_release lib/kobject.c:720 [inline]
 kref_put include/linux/kref.h:65 [inline]
 kobject_put+0x2b0/0x438 lib/kobject.c:737
 put_device+0x28/0x40 drivers/base/core.c:3797
 hci_free_dev+0x24/0x34 net/bluetooth/hci_core.c:2579
 vhci_release+0x134/0x17c drivers/bluetooth/hci_vhci.c:691
 __fput+0x340/0x75c fs/file_table.c:468
 ____fput+0x20/0x58 fs/file_table.c:496
 task_work_run+0x1dc/0x260 kernel/task_work.c:227
 exit_task_work include/linux/task_work.h:40 [inline]
 do_exit+0x524/0x1a14 kernel/exit.c:966
 do_group_exit+0x194/0x22c kernel/exit.c:1107
 get_signal+0x11dc/0x12f8 kernel/signal.c:3034
 arch_do_signal_or_restart+0x274/0x4414 arch/arm64/kernel/signal.c:1619
 exit_to_user_mode_loop+0x7c/0x178 kernel/entry/common.c:40
 exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
 arm64_exit_to_user_mode arch/arm64/kernel/entry-common.c:103 [inline]
 el0_svc+0x170/0x254 arch/arm64/kernel/entry-common.c:747
 el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:765
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596

Last potentially related work creation:
 kasan_save_stack+0x40/0x6c mm/kasan/common.c:56
 kasan_record_aux_stack+0xb0/0xc8 mm/kasan/generic.c:559
 insert_work+0x54/0x2cc kernel/workqueue.c:2186
 __queue_work+0xc88/0x1210 kernel/workqueue.c:2345
 queue_work_on+0xdc/0x18c kernel/workqueue.c:2392
 queue_work include/linux/workqueue.h:669 [inline]
 hci_cmd_timeout+0x178/0x1c8 net/bluetooth/hci_core.c:1480
 process_one_work+0x7e8/0x155c kernel/workqueue.c:3263
 process_scheduled_works kernel/workqueue.c:3346 [inline]
 worker_thread+0x958/0xed8 kernel/workqueue.c:3427
 kthread+0x5fc/0x75c kernel/kthread.c:463
 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:844

Second to last potentially related work creation:
 kasan_save_stack+0x40/0x6c mm/kasan/common.c:56
 kasan_record_aux_stack+0xb0/0xc8 mm/kasan/generic.c:559
 insert_work+0x54/0x2cc kernel/workqueue.c:2186
 __queue_work+0xdb0/0x1210 kernel/workqueue.c:2341
 delayed_work_timer_fn+0x74/0x90 kernel/workqueue.c:2487
 call_timer_fn+0x1b4/0x818 kernel/time/timer.c:1747
 expire_timers kernel/time/timer.c:1793 [inline]
 __run_timers kernel/time/timer.c:2372 [inline]
 __run_timer_base+0x54c/0x76c kernel/time/timer.c:2384
 run_timer_base kernel/time/timer.c:2393 [inline]
 run_timer_softirq+0xcc/0x194 kernel/time/timer.c:2403
 handle_softirqs+0x328/0xc88 kernel/softirq.c:622
 __do_softirq+0x14/0x20 kernel/softirq.c:656

The buggy address belongs to the object at ffff0000d69a8000
 which belongs to the cache kmalloc-8k of size 8192
The buggy address is located 160 bytes inside of
 freed 8192-byte region [ffff0000d69a8000, ffff0000d69aa000)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1169a8
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
anon flags: 0x5ffc00000000040(head|node=0|zone=2|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 05ffc00000000040 ffff0000c0002280 0000000000000000 0000000000000001
raw: 0000000000000000 0000000000020002 00000000f5000000 0000000000000000
head: 05ffc00000000040 ffff0000c0002280 0000000000000000 0000000000000001
head: 0000000000000000 0000000000020002 00000000f5000000 0000000000000000
head: 05ffc00000000003 fffffdffc35a6a01 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000008
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff0000d69a7f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff0000d69a8000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff0000d69a8080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                               ^
 ffff0000d69a8100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff0000d69a8180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


Tested on:

commit:         8d59fba4 Bluetooth: MGMT: Fix OOB access in parse_adv_..
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/bluetooth/bluetooth.git master
console output: https://syzkaller.appspot.com/x/log.txt?x=11a52084580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=5eeb63aaf73b06da
dashboard link: https://syzkaller.appspot.com/bug?extid=14b6d57fb728e27ce23c
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
userspace arch: arm64

Note: no patches were applied.

Re: [syzbot] [bluetooth?] KASAN: slab-use-after-free Read in l2cap_unregister_user

[shaurya]

#syz test: 
https://lore.kernel.org/all/20251105142251.101852-1-ssranevjti@gmail.com/T/

Re: [syzbot] [bluetooth?] KASAN: slab-use-after-free Read in l2cap_unregister_user

[syzbot]

> #syz test: 

I've failed to parse your command.
Did you perhaps forget to provide the branch name, or added an extra ':'?
Please use one of the two supported formats:
1. #syz test
2. #syz test: repo branch-or-commit-hash
Note the lack of ':' in option 1.

> https://lore.kernel.org/all/20251105142251.101852-1-ssranevjti@gmail.com/T/
>

Re: [syzbot] [bluetooth?] KASAN: slab-use-after-free Read in l2cap_unregister_user

[shaurya]

#syz test: 
https://lore.kernel.org/all/20251105142251.101852-1-ssranevjti@gmail.com/T/

Re: [syzbot] [bluetooth?] KASAN: slab-use-after-free Read in l2cap_unregister_user

[syzbot]

> #syz test: 

I've failed to parse your command.
Did you perhaps forget to provide the branch name, or added an extra ':'?
Please use one of the two supported formats:
1. #syz test
2. #syz test: repo branch-or-commit-hash
Note the lack of ':' in option 1.

> https://lore.kernel.org/all/20251105142251.101852-1-ssranevjti@gmail.com/T/
>

Re: [syzbot] [bluetooth?] KASAN: slab-use-after-free Read in l2cap_unregister_user

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
KASAN: slab-use-after-free Read in l2cap_unregister_user

==================================================================
BUG: KASAN: slab-use-after-free in __mutex_waiter_is_first kernel/locking/mutex.c:183 [inline]
BUG: KASAN: slab-use-after-free in __mutex_lock_common+0xd18/0x2678 kernel/locking/mutex.c:678
Read of size 8 at addr ffff0000de1180a0 by task khidpd_05c25886/7093

CPU: 0 UID: 0 PID: 7093 Comm: khidpd_05c25886 Not tainted syzkaller #0 PREEMPT 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/03/2025
Call trace:
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:499 (C)
 __dump_stack+0x30/0x40 lib/dump_stack.c:94
 dump_stack_lvl+0xd8/0x12c lib/dump_stack.c:120
 print_address_description+0xa8/0x238 mm/kasan/report.c:378
 print_report+0x68/0x84 mm/kasan/report.c:482
 kasan_report+0xb0/0x110 mm/kasan/report.c:595
 __asan_report_load8_noabort+0x20/0x2c mm/kasan/report_generic.c:381
 __mutex_waiter_is_first kernel/locking/mutex.c:183 [inline]
 __mutex_lock_common+0xd18/0x2678 kernel/locking/mutex.c:678
 __mutex_lock kernel/locking/mutex.c:760 [inline]
 mutex_lock_nested+0x2c/0x38 kernel/locking/mutex.c:812
 l2cap_unregister_user+0x74/0x190 net/bluetooth/l2cap_core.c:1728
 hidp_session_thread+0x3d0/0x46c net/bluetooth/hidp/core.c:1304
 kthread+0x5fc/0x75c kernel/kthread.c:463
 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:844

Allocated by task 6997:
 kasan_save_stack mm/kasan/common.c:56 [inline]
 kasan_save_track+0x40/0x78 mm/kasan/common.c:77
 kasan_save_alloc_info+0x44/0x54 mm/kasan/generic.c:573
 poison_kmalloc_redzone mm/kasan/common.c:400 [inline]
 __kasan_kmalloc+0x9c/0xb4 mm/kasan/common.c:417
 kasan_kmalloc include/linux/kasan.h:262 [inline]
 __do_kmalloc_node mm/slub.c:5642 [inline]
 __kmalloc_noprof+0x3fc/0x728 mm/slub.c:5654
 kmalloc_noprof include/linux/slab.h:961 [inline]
 kzalloc_noprof include/linux/slab.h:1094 [inline]
 hci_alloc_dev_priv+0x2c/0x1b84 net/bluetooth/hci_core.c:2448
 hci_alloc_dev include/net/bluetooth/hci_core.h:1751 [inline]
 __vhci_create_device drivers/bluetooth/hci_vhci.c:421 [inline]
 vhci_create_device+0x108/0x638 drivers/bluetooth/hci_vhci.c:479
 vhci_get_user drivers/bluetooth/hci_vhci.c:536 [inline]
 vhci_write+0x314/0x3d4 drivers/bluetooth/hci_vhci.c:616
 new_sync_write fs/read_write.c:593 [inline]
 vfs_write+0x540/0xa3c fs/read_write.c:686
 ksys_write+0x120/0x210 fs/read_write.c:738
 __do_sys_write fs/read_write.c:749 [inline]
 __se_sys_write fs/read_write.c:746 [inline]
 __arm64_sys_write+0x7c/0x90 fs/read_write.c:746
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall+0x98/0x254 arch/arm64/kernel/syscall.c:49
 el0_svc_common+0x130/0x23c arch/arm64/kernel/syscall.c:132
 do_el0_svc+0x48/0x58 arch/arm64/kernel/syscall.c:151
 el0_svc+0x5c/0x254 arch/arm64/kernel/entry-common.c:746
 el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:765
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596

Freed by task 7412:
 kasan_save_stack mm/kasan/common.c:56 [inline]
 kasan_save_track+0x40/0x78 mm/kasan/common.c:77
 __kasan_save_free_info+0x58/0x70 mm/kasan/generic.c:587
 kasan_save_free_info mm/kasan/kasan.h:406 [inline]
 poison_slab_object mm/kasan/common.c:252 [inline]
 __kasan_slab_free+0x74/0xa4 mm/kasan/common.c:284
 kasan_slab_free include/linux/kasan.h:234 [inline]
 slab_free_hook mm/slub.c:2539 [inline]
 slab_free mm/slub.c:6630 [inline]
 kfree+0x184/0x600 mm/slub.c:6837
 hci_release_dev+0xf48/0x1060 net/bluetooth/hci_core.c:2776
 bt_host_release+0x70/0x8c net/bluetooth/hci_sysfs.c:87
 device_release+0x8c/0x1ac drivers/base/core.c:-1
 kobject_cleanup lib/kobject.c:689 [inline]
 kobject_release lib/kobject.c:720 [inline]
 kref_put include/linux/kref.h:65 [inline]
 kobject_put+0x2b0/0x438 lib/kobject.c:737
 put_device+0x28/0x40 drivers/base/core.c:3797
 hci_free_dev+0x24/0x34 net/bluetooth/hci_core.c:2579
 vhci_release+0x134/0x17c drivers/bluetooth/hci_vhci.c:691
 __fput+0x340/0x75c fs/file_table.c:468
 ____fput+0x20/0x58 fs/file_table.c:496
 task_work_run+0x1dc/0x260 kernel/task_work.c:227
 exit_task_work include/linux/task_work.h:40 [inline]
 do_exit+0x524/0x1a14 kernel/exit.c:966
 do_group_exit+0x194/0x22c kernel/exit.c:1107
 get_signal+0x11dc/0x12f8 kernel/signal.c:3034
 arch_do_signal_or_restart+0x274/0x4414 arch/arm64/kernel/signal.c:1619
 exit_to_user_mode_loop+0x7c/0x178 kernel/entry/common.c:40
 exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
 arm64_exit_to_user_mode arch/arm64/kernel/entry-common.c:103 [inline]
 el0_svc+0x170/0x254 arch/arm64/kernel/entry-common.c:747
 el0t_64_sync_handler+0x84/0x12c arch/arm64/kernel/entry-common.c:765
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:596

Last potentially related work creation:
 kasan_save_stack+0x40/0x6c mm/kasan/common.c:56
 kasan_record_aux_stack+0xb0/0xc8 mm/kasan/generic.c:559
 insert_work+0x54/0x2cc kernel/workqueue.c:2186
 __queue_work+0xc88/0x1210 kernel/workqueue.c:2345
 queue_work_on+0xdc/0x18c kernel/workqueue.c:2392
 queue_work include/linux/workqueue.h:669 [inline]
 hci_cmd_timeout+0x178/0x1c8 net/bluetooth/hci_core.c:1480
 process_one_work+0x7e8/0x155c kernel/workqueue.c:3263
 process_scheduled_works kernel/workqueue.c:3346 [inline]
 worker_thread+0x958/0xed8 kernel/workqueue.c:3427
 kthread+0x5fc/0x75c kernel/kthread.c:463
 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:844

Second to last potentially related work creation:
 kasan_save_stack+0x40/0x6c mm/kasan/common.c:56
 kasan_record_aux_stack+0xb0/0xc8 mm/kasan/generic.c:559
 insert_work+0x54/0x2cc kernel/workqueue.c:2186
 __queue_work+0xdb0/0x1210 kernel/workqueue.c:2341
 delayed_work_timer_fn+0x74/0x90 kernel/workqueue.c:2487
 call_timer_fn+0x1b4/0x818 kernel/time/timer.c:1747
 expire_timers kernel/time/timer.c:1793 [inline]
 __run_timers kernel/time/timer.c:2372 [inline]
 __run_timer_base+0x54c/0x76c kernel/time/timer.c:2384
 run_timer_base kernel/time/timer.c:2393 [inline]
 run_timer_softirq+0xcc/0x194 kernel/time/timer.c:2403
 handle_softirqs+0x328/0xc88 kernel/softirq.c:622
 __do_softirq+0x14/0x20 kernel/softirq.c:656

The buggy address belongs to the object at ffff0000de118000
 which belongs to the cache kmalloc-8k of size 8192
The buggy address is located 160 bytes inside of
 freed 8192-byte region [ffff0000de118000, ffff0000de11a000)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x11e118
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
anon flags: 0x5ffc00000000040(head|node=0|zone=2|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 05ffc00000000040 ffff0000c0002280 0000000000000000 dead000000000001
raw: 0000000000000000 0000000000020002 00000000f5000000 0000000000000000
head: 05ffc00000000040 ffff0000c0002280 0000000000000000 dead000000000001
head: 0000000000000000 0000000000020002 00000000f5000000 0000000000000000
head: 05ffc00000000003 fffffdffc3784601 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000008
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff0000de117f80: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff0000de118000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff0000de118080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                               ^
 ffff0000de118100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff0000de118180: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


Tested on:

commit:         8d59fba4 Bluetooth: MGMT: Fix OOB access in parse_adv_..
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/bluetooth/bluetooth.git master
console output: https://syzkaller.appspot.com/x/log.txt?x=14d9a532580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=5eeb63aaf73b06da
dashboard link: https://syzkaller.appspot.com/bug?extid=14b6d57fb728e27ce23c
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
userspace arch: arm64

Note: no patches were applied.

Forwarded: Re: [RESEND] Bluetooth: L2CAP: Fix use-after-free in l2cap_unregister_user

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com.

***

Subject: Re: [RESEND] Bluetooth: L2CAP: Fix use-after-free in l2cap_unregister_user
Author: pav@iki.fi

pe, 2026-03-06 kello 16:04 -0500, Luiz Augusto von Dentz kirjoitti:
> From: Shaurya Rane <ssrane_b23@ee.vjti.ac.in>
> 
> After commit ab4eedb790ca ("Bluetooth: L2CAP: Fix corrupted list in
> hci_chan_del"), l2cap_conn_del() uses conn->lock to protect access to
> conn->users and conn->hchan. However, l2cap_register_user() and
> l2cap_unregister_user() still use hci_dev_lock(), creating a race
> condition where these functions can access conn->users and conn->hchan
> concurrently with l2cap_conn_del().

AFAIK the above text from the original submitter is a bit inaccurate,
as l2cap_conn_del() is called with hdev lock held, so conn->users/hchan
should be safe.

However, using conn->mutex should fix the use-after-free in

	conn->hcon->hdev
	hci_dev_lock(hdev);
	hci_dev_unlock(hdev);

by making l2cap_unregister_user() safe to call after the hcon/hdev are
no longer alive.

The change looks OK to me, but probably worth to double check with
syzbot it fixes the original issue

#syz test git://git.kernel.org/pub/scm/linux/kernel/git/bluetooth/bluetooth-next.git master

> This can lead to use-after-free and list corruption bugs, as reported
> by syzbot.
> 
> Fix this by changing l2cap_register_user() and l2cap_unregister_user()
> to use conn->lock instead of hci_dev_lock(), ensuring consistent locking
> for the l2cap_conn structure.
> Reported-by: syzbot+14b6d57fb728e27ce23c@syzkaller.appspotmail.com
> Closes: https://syzkaller.appspot.com/bug?extid=14b6d57fb728e27ce23c
> Fixes: ab4eedb790ca ("Bluetooth: L2CAP: Fix corrupted list in hci_chan_del")
> Signed-off-by: Shaurya Rane <ssrane_b23@ee.vjti.ac.in>
> Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
> ---
>  net/bluetooth/l2cap_core.c | 20 ++++++++------------
>  1 file changed, 8 insertions(+), 12 deletions(-)
> 
> diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
> index 14131e427efd..6606d7f12534 100644
> --- a/net/bluetooth/l2cap_core.c
> +++ b/net/bluetooth/l2cap_core.c
> @@ -1678,17 +1678,15 @@ static void l2cap_info_timeout(struct work_struct *work)
>  
>  int l2cap_register_user(struct l2cap_conn *conn, struct l2cap_user *user)
>  {
> -	struct hci_dev *hdev = conn->hcon->hdev;
>  	int ret;
>  
>  	/* We need to check whether l2cap_conn is registered. If it is not, we
> -	 * must not register the l2cap_user. l2cap_conn_del() is unregisters
> -	 * l2cap_conn objects, but doesn't provide its own locking. Instead, it
> -	 * relies on the parent hci_conn object to be locked. This itself relies
> -	 * on the hci_dev object to be locked. So we must lock the hci device
> -	 * here, too. */
> +	 * must not register the l2cap_user. l2cap_conn_del() unregisters
> +	 * l2cap_conn objects under conn->lock, and we use the same lock here
> +	 * to protect access to conn->users and conn->hchan.
> +	 */
>  
> -	hci_dev_lock(hdev);
> +	mutex_lock(&conn->lock);
>  
>  	if (!list_empty(&user->list)) {
>  		ret = -EINVAL;
> @@ -1709,16 +1707,14 @@ int l2cap_register_user(struct l2cap_conn *conn, struct l2cap_user *user)
>  	ret = 0;
>  
>  out_unlock:
> -	hci_dev_unlock(hdev);
> +	mutex_unlock(&conn->lock);
>  	return ret;
>  }
>  EXPORT_SYMBOL(l2cap_register_user);
>  
>  void l2cap_unregister_user(struct l2cap_conn *conn, struct l2cap_user *user)
>  {
> -	struct hci_dev *hdev = conn->hcon->hdev;
> -
> -	hci_dev_lock(hdev);
> +	mutex_lock(&conn->lock);
>  
>  	if (list_empty(&user->list))
>  		goto out_unlock;
> @@ -1727,7 +1723,7 @@ void l2cap_unregister_user(struct l2cap_conn *conn, struct l2cap_user *user)
>  	user->remove(conn, user);
>  
>  out_unlock:
> -	hci_dev_unlock(hdev);
> +	mutex_unlock(&conn->lock);
>  }
>  EXPORT_SYMBOL(l2cap_unregister_user);
>  

Re: [syzbot] [bluetooth?] KASAN: slab-use-after-free Read in l2cap_unregister_user

[syzbot]

Hello,

syzbot tried to test the proposed patch but the build/boot failed:

can't ssh into the instance



failed to run ["ssh" "-p" "22" "-F" "/dev/null" "-o" "UserKnownHostsFile=/dev/null" "-o" "IdentitiesOnly=yes" "-o" "BatchMode=yes" "-o" "StrictHostKeyChecking=no" "-o" "ConnectTimeout=10" "root@10.128.1.205" "pwd"]: exit status 255Pseudo-terminal will not be allocated because stdin is not a terminal.
Warning: Permanently added '[us-central1-ssh-serialport.googleapis.com]:9600' (ECDSA) to the list of known hosts.
UEFI firmware (version  built at 09:00:00 on Jan 10 2025)
EMU Variable FVB Started
EMU Variable invalid PCD sizes
Found PL031 RTC @ 0x9010000
InitializeRealTimeClock: using default timezone/daylight settings
^[[2J^[[01;01H^[[=3h^[[2J^[[01;01H^[[2J^[[01;01H^[[=3h^[[2J^[[01;01HBdsDxe: loading Boot0001 "UEFI Misc Device" from PciRoot(0x0)/Pci(0x2,0x0)/NVMe(0x1,00-00-00-00-00-00-00-00)
BdsDxe: starting Boot0001 "UEFI Misc Device" from PciRoot(0x0)/Pci(0x2,0x0)/NVMe(0x1,00-00-00-00-00-00-00-00)

UEFI: Attempting to start image.
Description: UEFI Misc Device
FilePath: PciRoot(0x0)/Pci(0x2,0x0)/NVMe(0x1,00-00-00-00-00-00-00-00)
OptionNumber: 1.

  Booting `syzkaller'


serialport: Connected to syzkaller.us-central1-a.ci-upstream-gce-arm64-test-job-parallel-1 port 1 (session ID: 0999632978e2591e762757af145c8d34989ebc3ddb04e2e60c08a78fd4beda56, active connections: 1).


syzkaller build log:
go env (err=<nil>)
AR='ar'
CC='gcc'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='g++'
GCCGO='gccgo'
GO111MODULE='auto'
GOAMD64='v1'
GOARCH='amd64'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/syzkaller/.cache/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/syzkaller/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build2562130928=/tmp/go-build -gno-record-gcc-switches'
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMOD='/syzkaller/jobs-2/linux/gopath/src/github.com/google/syzkaller/go.mod'
GOMODCACHE='/syzkaller/jobs-2/linux/gopath/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/syzkaller/jobs-2/linux/gopath'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/syzkaller/.config/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.26.0'
GOWORK=''
PKG_CONFIG='pkg-config'

git status (err=<nil>)
HEAD detached at c06e8995d7
nothing to commit, working tree clean


tput: No value for $TERM and no -T specified
tput: No value for $TERM and no -T specified
Makefile:31: run command via tools/syz-env for best compatibility, see:
Makefile:32: https://github.com/google/syzkaller/blob/master/docs/contributing.md#using-syz-env
go list -f '{{.Stale}}' ./sys/syz-sysgen | grep -q false || go install ./sys/syz-sysgen
make .descriptions
tput: No value for $TERM and no -T specified
tput: No value for $TERM and no -T specified
Makefile:31: run command via tools/syz-env for best compatibility, see:
Makefile:32: https://github.com/google/syzkaller/blob/master/docs/contributing.md#using-syz-env
bin/syz-sysgen
touch .descriptions
GOOS=linux GOARCH=arm64 go build -ldflags="-s -w -X github.com/google/syzkaller/prog.GitRevision=c06e8995d711b5a8d8fbd771826fcbfdac6f110f -X github.com/google/syzkaller/prog.gitRevisionDate=20250811-165554"  -o ./bin/linux_arm64/syz-execprog github.com/google/syzkaller/tools/syz-execprog
mkdir -p ./bin/linux_arm64
aarch64-linux-gnu-g++ -o ./bin/linux_arm64/syz-executor executor/executor.cc \
	-O2 -pthread -Wall -Werror -Wparentheses -Wunused-const-variable -Wframe-larger-than=16384 -Wno-stringop-overflow -Wno-array-bounds -Wno-format-overflow -Wno-unused-but-set-variable -Wno-unused-command-line-argument -static-pie -std=c++17 -I. -Iexecutor/_include   -DGOOS_linux=1 -DGOARCH_arm64=1 \
	-DHOSTGOOS_linux=1 -DGIT_REVISION=\"c06e8995d711b5a8d8fbd771826fcbfdac6f110f\"
/usr/lib/gcc-cross/aarch64-linux-gnu/14/../../../../aarch64-linux-gnu/bin/ld: /tmp/ccd7e8uY.o: in function `Connection::Connect(char const*, char const*)':
executor.cc:(.text._ZN10Connection7ConnectEPKcS1_[_ZN10Connection7ConnectEPKcS1_]+0x2ec): warning: Using 'gethostbyname' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking



Tested on:

commit:         708efc5f Bluetooth: HIDP: Fix possible UAF
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/bluetooth/bluetooth-next.git master
kernel config:  https://syzkaller.appspot.com/x/.config?x=de187e3c06ea9a2b
dashboard link: https://syzkaller.appspot.com/bug?extid=14b6d57fb728e27ce23c
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
userspace arch: arm64
patch:          https://syzkaller.appspot.com/x/patch.diff?x=11b8075a580000

Forwarded: Re: [RESEND] Bluetooth: L2CAP: Fix use-after-free in l2cap_unregister_user

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com.

***

Subject: Re: [RESEND] Bluetooth: L2CAP: Fix use-after-free in l2cap_unregister_user
Author: pav@iki.fi

la, 2026-03-07 kello 10:59 +0200, Pauli Virtanen kirjoitti:
> pe, 2026-03-06 kello 16:04 -0500, Luiz Augusto von Dentz kirjoitti:
> > From: Shaurya Rane <ssrane_b23@ee.vjti.ac.in>
> > 
> > After commit ab4eedb790ca ("Bluetooth: L2CAP: Fix corrupted list in
> > hci_chan_del"), l2cap_conn_del() uses conn->lock to protect access to
> > conn->users and conn->hchan. However, l2cap_register_user() and
> > l2cap_unregister_user() still use hci_dev_lock(), creating a race
> > condition where these functions can access conn->users and conn->hchan
> > concurrently with l2cap_conn_del().
> 
> AFAIK the above text from the original submitter is a bit inaccurate,
> as l2cap_conn_del() is called with hdev lock held, so conn->users/hchan
> should be safe.
> 
> However, using conn->mutex should fix the use-after-free in
> 
> 	conn->hcon->hdev
> 	hci_dev_lock(hdev);
> 	hci_dev_unlock(hdev);
> 
> by making l2cap_unregister_user() safe to call after the hcon/hdev are
> no longer alive.
> 
> The change looks OK to me, but probably worth to double check with
> syzbot it fixes the original issue

syzbot seems to have hit some internal error, another try on upstream
branch instead

#syz test

> > This can lead to use-after-free and list corruption bugs, as reported
> > by syzbot.
> > 
> > Fix this by changing l2cap_register_user() and l2cap_unregister_user()
> > to use conn->lock instead of hci_dev_lock(), ensuring consistent locking
> > for the l2cap_conn structure.
> > Reported-by: syzbot+14b6d57fb728e27ce23c@syzkaller.appspotmail.com
> > Closes: https://syzkaller.appspot.com/bug?extid=14b6d57fb728e27ce23c
> > Fixes: ab4eedb790ca ("Bluetooth: L2CAP: Fix corrupted list in hci_chan_del")
> > Signed-off-by: Shaurya Rane <ssrane_b23@ee.vjti.ac.in>
> > Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
> > ---
> >  net/bluetooth/l2cap_core.c | 20 ++++++++------------
> >  1 file changed, 8 insertions(+), 12 deletions(-)
> > 
> > diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
> > index 14131e427efd..6606d7f12534 100644
> > --- a/net/bluetooth/l2cap_core.c
> > +++ b/net/bluetooth/l2cap_core.c
> > @@ -1678,17 +1678,15 @@ static void l2cap_info_timeout(struct work_struct *work)
> >  
> >  int l2cap_register_user(struct l2cap_conn *conn, struct l2cap_user *user)
> >  {
> > -	struct hci_dev *hdev = conn->hcon->hdev;
> >  	int ret;
> >  
> >  	/* We need to check whether l2cap_conn is registered. If it is not, we
> > -	 * must not register the l2cap_user. l2cap_conn_del() is unregisters
> > -	 * l2cap_conn objects, but doesn't provide its own locking. Instead, it
> > -	 * relies on the parent hci_conn object to be locked. This itself relies
> > -	 * on the hci_dev object to be locked. So we must lock the hci device
> > -	 * here, too. */
> > +	 * must not register the l2cap_user. l2cap_conn_del() unregisters
> > +	 * l2cap_conn objects under conn->lock, and we use the same lock here
> > +	 * to protect access to conn->users and conn->hchan.
> > +	 */
> >  
> > -	hci_dev_lock(hdev);
> > +	mutex_lock(&conn->lock);
> >  
> >  	if (!list_empty(&user->list)) {
> >  		ret = -EINVAL;
> > @@ -1709,16 +1707,14 @@ int l2cap_register_user(struct l2cap_conn *conn, struct l2cap_user *user)
> >  	ret = 0;
> >  
> >  out_unlock:
> > -	hci_dev_unlock(hdev);
> > +	mutex_unlock(&conn->lock);
> >  	return ret;
> >  }
> >  EXPORT_SYMBOL(l2cap_register_user);
> >  
> >  void l2cap_unregister_user(struct l2cap_conn *conn, struct l2cap_user *user)
> >  {
> > -	struct hci_dev *hdev = conn->hcon->hdev;
> > -
> > -	hci_dev_lock(hdev);
> > +	mutex_lock(&conn->lock);
> >  
> >  	if (list_empty(&user->list))
> >  		goto out_unlock;
> > @@ -1727,7 +1723,7 @@ void l2cap_unregister_user(struct l2cap_conn *conn, struct l2cap_user *user)
> >  	user->remove(conn, user);
> >  
> >  out_unlock:
> > -	hci_dev_unlock(hdev);
> > +	mutex_unlock(&conn->lock);
> >  }
> >  EXPORT_SYMBOL(l2cap_unregister_user);
> >  

Re: [syzbot] [bluetooth?] KASAN: slab-use-after-free Read in l2cap_unregister_user

[syzbot]

Hello,

syzbot tried to test the proposed patch but the build/boot failed:

can't ssh into the instance



failed to run ["ssh" "-p" "22" "-F" "/dev/null" "-o" "UserKnownHostsFile=/dev/null" "-o" "IdentitiesOnly=yes" "-o" "BatchMode=yes" "-o" "StrictHostKeyChecking=no" "-o" "ConnectTimeout=10" "root@10.128.1.197" "pwd"]: exit status 255Pseudo-terminal will not be allocated because stdin is not a terminal.
Warning: Permanently added '[us-central1-ssh-serialport.googleapis.com]:9600' (ECDSA) to the list of known hosts.
UEFI firmware (version  built at 09:00:00 on Jan 10 2025)
EMU Variable FVB Started
EMU Variable invalid PCD sizes
Found PL031 RTC @ 0x9010000
InitializeRealTimeClock: using default timezone/daylight settings
^[[2J^[[01;01H^[[=3h^[[2J^[[01;01H^[[2J^[[01;01H^[[=3h^[[2J^[[01;01HBdsDxe: loading Boot0001 "UEFI Misc Device" from PciRoot(0x0)/Pci(0x2,0x0)/NVMe(0x1,00-00-00-00-00-00-00-00)
BdsDxe: starting Boot0001 "UEFI Misc Device" from PciRoot(0x0)/Pci(0x2,0x0)/NVMe(0x1,00-00-00-00-00-00-00-00)

UEFI: Attempting to start image.
Description: UEFI Misc Device
FilePath: PciRoot(0x0)/Pci(0x2,0x0)/NVMe(0x1,00-00-00-00-00-00-00-00)
OptionNumber: 1.

  Booting `syzkaller'


serialport: Connected to syzkaller.us-central1-a.ci-upstream-gce-arm64-test-job-parallel-1 port 1 (session ID: 496df2a91bf6754c27cb2596a739f60f4c94c5a4fc85884e1f75d06230ee71eb, active connections: 1).


syzkaller build log:
go env (err=<nil>)
AR='ar'
CC='gcc'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='g++'
GCCGO='gccgo'
GO111MODULE='auto'
GOAMD64='v1'
GOARCH='amd64'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/syzkaller/.cache/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/syzkaller/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build262281762=/tmp/go-build -gno-record-gcc-switches'
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMOD='/syzkaller/jobs-2/linux/gopath/src/github.com/google/syzkaller/go.mod'
GOMODCACHE='/syzkaller/jobs-2/linux/gopath/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/syzkaller/jobs-2/linux/gopath'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/syzkaller/.config/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.26.0'
GOWORK=''
PKG_CONFIG='pkg-config'

git status (err=<nil>)
HEAD detached at c06e8995d7
nothing to commit, working tree clean


tput: No value for $TERM and no -T specified
tput: No value for $TERM and no -T specified
Makefile:31: run command via tools/syz-env for best compatibility, see:
Makefile:32: https://github.com/google/syzkaller/blob/master/docs/contributing.md#using-syz-env
go list -f '{{.Stale}}' ./sys/syz-sysgen | grep -q false || go install ./sys/syz-sysgen
make .descriptions
tput: No value for $TERM and no -T specified
tput: No value for $TERM and no -T specified
Makefile:31: run command via tools/syz-env for best compatibility, see:
Makefile:32: https://github.com/google/syzkaller/blob/master/docs/contributing.md#using-syz-env
bin/syz-sysgen
touch .descriptions
GOOS=linux GOARCH=arm64 go build -ldflags="-s -w -X github.com/google/syzkaller/prog.GitRevision=c06e8995d711b5a8d8fbd771826fcbfdac6f110f -X github.com/google/syzkaller/prog.gitRevisionDate=20250811-165554"  -o ./bin/linux_arm64/syz-execprog github.com/google/syzkaller/tools/syz-execprog
mkdir -p ./bin/linux_arm64
aarch64-linux-gnu-g++ -o ./bin/linux_arm64/syz-executor executor/executor.cc \
	-O2 -pthread -Wall -Werror -Wparentheses -Wunused-const-variable -Wframe-larger-than=16384 -Wno-stringop-overflow -Wno-array-bounds -Wno-format-overflow -Wno-unused-but-set-variable -Wno-unused-command-line-argument -static-pie -std=c++17 -I. -Iexecutor/_include   -DGOOS_linux=1 -DGOARCH_arm64=1 \
	-DHOSTGOOS_linux=1 -DGIT_REVISION=\"c06e8995d711b5a8d8fbd771826fcbfdac6f110f\"
/usr/lib/gcc-cross/aarch64-linux-gnu/14/../../../../aarch64-linux-gnu/bin/ld: /tmp/ccHQpBys.o: in function `Connection::Connect(char const*, char const*)':
executor.cc:(.text._ZN10Connection7ConnectEPKcS1_[_ZN10Connection7ConnectEPKcS1_]+0x2ec): warning: Using 'gethostbyname' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking



Tested on:

commit:         1e0a8362 Merge branches 'for-next/core' and 'for-next/..
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
kernel config:  https://syzkaller.appspot.com/x/.config?x=1aef92cd87e68b9f
dashboard link: https://syzkaller.appspot.com/bug?extid=14b6d57fb728e27ce23c
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
userspace arch: arm64
patch:          https://syzkaller.appspot.com/x/patch.diff?x=10e4075a580000

Forwarded: Re: [RESEND] Bluetooth: L2CAP: Fix use-after-free in l2cap_unregister_user

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org, syzkaller-bugs@googlegroups.com.

***

Subject: Re: [RESEND] Bluetooth: L2CAP: Fix use-after-free in l2cap_unregister_user
Author: pav@iki.fi

la, 2026-03-07 kello 11:45 +0200, Pauli Virtanen kirjoitti:
> la, 2026-03-07 kello 10:59 +0200, Pauli Virtanen kirjoitti:
> > pe, 2026-03-06 kello 16:04 -0500, Luiz Augusto von Dentz kirjoitti:
> > > From: Shaurya Rane <ssrane_b23@ee.vjti.ac.in>
> > > 
> > > After commit ab4eedb790ca ("Bluetooth: L2CAP: Fix corrupted list in
> > > hci_chan_del"), l2cap_conn_del() uses conn->lock to protect access to
> > > conn->users and conn->hchan. However, l2cap_register_user() and
> > > l2cap_unregister_user() still use hci_dev_lock(), creating a race
> > > condition where these functions can access conn->users and conn->hchan
> > > concurrently with l2cap_conn_del().
> > 
> > AFAIK the above text from the original submitter is a bit inaccurate,
> > as l2cap_conn_del() is called with hdev lock held, so conn->users/hchan
> > should be safe.
> > 
> > However, using conn->mutex should fix the use-after-free in
> > 
> > 	conn->hcon->hdev
> > 	hci_dev_lock(hdev);
> > 	hci_dev_unlock(hdev);
> > 
> > by making l2cap_unregister_user() safe to call after the hcon/hdev are
> > no longer alive.
> > 
> > The change looks OK to me, but probably worth to double check with
> > syzbot it fixes the original issue
> 
> syzbot seems to have hit some internal error, another try on upstream
> branch instead
> 

No luck, test the patch setting session->conn = NULL; in case it fixes
the syzcaller failure. If that passes, maybe the conn->mutex locking
overlooks something that I don't see right now,

#syz test

> > > This can lead to use-after-free and list corruption bugs, as reported
> > > by syzbot.
> > > 
> > > Fix this by changing l2cap_register_user() and l2cap_unregister_user()
> > > to use conn->lock instead of hci_dev_lock(), ensuring consistent locking
> > > for the l2cap_conn structure.
> > > Reported-by: syzbot+14b6d57fb728e27ce23c@syzkaller.appspotmail.com
> > > Closes: https://syzkaller.appspot.com/bug?extid=14b6d57fb728e27ce23c
> > > Fixes: ab4eedb790ca ("Bluetooth: L2CAP: Fix corrupted list in hci_chan_del")
> > > Signed-off-by: Shaurya Rane <ssrane_b23@ee.vjti.ac.in>
> > > Signed-off-by: Luiz Augusto von Dentz <luiz.von.dentz@intel.com>
> > > ---
> > >  net/bluetooth/l2cap_core.c | 20 ++++++++------------
> > >  1 file changed, 8 insertions(+), 12 deletions(-)
> > > 
> > > diff --git a/net/bluetooth/l2cap_core.c b/net/bluetooth/l2cap_core.c
> > > index 14131e427efd..6606d7f12534 100644
> > > --- a/net/bluetooth/l2cap_core.c
> > > +++ b/net/bluetooth/l2cap_core.c
> > > @@ -1678,17 +1678,15 @@ static void l2cap_info_timeout(struct work_struct *work)
> > >  
> > >  int l2cap_register_user(struct l2cap_conn *conn, struct l2cap_user *user)
> > >  {
> > > -	struct hci_dev *hdev = conn->hcon->hdev;
> > >  	int ret;
> > >  
> > >  	/* We need to check whether l2cap_conn is registered. If it is not, we
> > > -	 * must not register the l2cap_user. l2cap_conn_del() is unregisters
> > > -	 * l2cap_conn objects, but doesn't provide its own locking. Instead, it
> > > -	 * relies on the parent hci_conn object to be locked. This itself relies
> > > -	 * on the hci_dev object to be locked. So we must lock the hci device
> > > -	 * here, too. */
> > > +	 * must not register the l2cap_user. l2cap_conn_del() unregisters
> > > +	 * l2cap_conn objects under conn->lock, and we use the same lock here
> > > +	 * to protect access to conn->users and conn->hchan.
> > > +	 */
> > >  
> > > -	hci_dev_lock(hdev);
> > > +	mutex_lock(&conn->lock);
> > >  
> > >  	if (!list_empty(&user->list)) {
> > >  		ret = -EINVAL;
> > > @@ -1709,16 +1707,14 @@ int l2cap_register_user(struct l2cap_conn *conn, struct l2cap_user *user)
> > >  	ret = 0;
> > >  
> > >  out_unlock:
> > > -	hci_dev_unlock(hdev);
> > > +	mutex_unlock(&conn->lock);
> > >  	return ret;
> > >  }
> > >  EXPORT_SYMBOL(l2cap_register_user);
> > >  
> > >  void l2cap_unregister_user(struct l2cap_conn *conn, struct l2cap_user *user)
> > >  {
> > > -	struct hci_dev *hdev = conn->hcon->hdev;
> > > -
> > > -	hci_dev_lock(hdev);
> > > +	mutex_lock(&conn->lock);
> > >  
> > >  	if (list_empty(&user->list))
> > >  		goto out_unlock;
> > > @@ -1727,7 +1723,7 @@ void l2cap_unregister_user(struct l2cap_conn *conn, struct l2cap_user *user)
> > >  	user->remove(conn, user);
> > >  
> > >  out_unlock:
> > > -	hci_dev_unlock(hdev);
> > > +	mutex_unlock(&conn->lock);
> > >  }
> > >  EXPORT_SYMBOL(l2cap_unregister_user);
> > >  

Re: [syzbot] [bluetooth?] KASAN: slab-use-after-free Read in l2cap_unregister_user

[syzbot]

Hello,

syzbot tried to test the proposed patch but the build/boot failed:

can't ssh into the instance



failed to run ["ssh" "-p" "22" "-F" "/dev/null" "-o" "UserKnownHostsFile=/dev/null" "-o" "IdentitiesOnly=yes" "-o" "BatchMode=yes" "-o" "StrictHostKeyChecking=no" "-o" "ConnectTimeout=10" "root@10.128.0.96" "pwd"]: exit status 255Pseudo-terminal will not be allocated because stdin is not a terminal.
Warning: Permanently added '[us-central1-ssh-serialport.googleapis.com]:9600' (ECDSA) to the list of known hosts.
UEFI firmware (version  built at 09:00:00 on Jan 10 2025)
EMU Variable FVB Started
EMU Variable invalid PCD sizes
Found PL031 RTC @ 0x9010000
InitializeRealTimeClock: using default timezone/daylight settings
^[[2J^[[01;01H^[[=3h^[[2J^[[01;01H^[[2J^[[01;01H^[[=3h^[[2J^[[01;01HBdsDxe: loading Boot0001 "UEFI Misc Device" from PciRoot(0x0)/Pci(0x2,0x0)/NVMe(0x1,00-00-00-00-00-00-00-00)
BdsDxe: starting Boot0001 "UEFI Misc Device" from PciRoot(0x0)/Pci(0x2,0x0)/NVMe(0x1,00-00-00-00-00-00-00-00)

UEFI: Attempting to start image.
Description: UEFI Misc Device
FilePath: PciRoot(0x0)/Pci(0x2,0x0)/NVMe(0x1,00-00-00-00-00-00-00-00)
OptionNumber: 1.

  Booting `syzkaller'


serialport: Connected to syzkaller.us-central1-a.ci-upstream-gce-arm64-test-job-2 port 1 (session ID: bb7bd93cd4db56d08e3e26793aff3031016e820757ae311fc18736e74b75bf59, active connections: 1).


syzkaller build log:
go env (err=<nil>)
AR='ar'
CC='gcc'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='g++'
GCCGO='gccgo'
GO111MODULE='auto'
GOAMD64='v1'
GOARCH='amd64'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/syzkaller/.cache/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/syzkaller/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build165225799=/tmp/go-build -gno-record-gcc-switches'
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMOD='/syzkaller/jobs/linux/gopath/src/github.com/google/syzkaller/go.mod'
GOMODCACHE='/syzkaller/jobs/linux/gopath/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/syzkaller/jobs/linux/gopath'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/syzkaller/.config/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.26.0'
GOWORK=''
PKG_CONFIG='pkg-config'

git status (err=<nil>)
HEAD detached at c06e8995d71
nothing to commit, working tree clean


tput: No value for $TERM and no -T specified
tput: No value for $TERM and no -T specified
Makefile:31: run command via tools/syz-env for best compatibility, see:
Makefile:32: https://github.com/google/syzkaller/blob/master/docs/contributing.md#using-syz-env
go list -f '{{.Stale}}' ./sys/syz-sysgen | grep -q false || go install ./sys/syz-sysgen
make .descriptions
tput: No value for $TERM and no -T specified
tput: No value for $TERM and no -T specified
Makefile:31: run command via tools/syz-env for best compatibility, see:
Makefile:32: https://github.com/google/syzkaller/blob/master/docs/contributing.md#using-syz-env
bin/syz-sysgen
touch .descriptions
GOOS=linux GOARCH=arm64 go build -ldflags="-s -w -X github.com/google/syzkaller/prog.GitRevision=c06e8995d711b5a8d8fbd771826fcbfdac6f110f -X github.com/google/syzkaller/prog.gitRevisionDate=20250811-165554"  -o ./bin/linux_arm64/syz-execprog github.com/google/syzkaller/tools/syz-execprog
mkdir -p ./bin/linux_arm64
aarch64-linux-gnu-g++ -o ./bin/linux_arm64/syz-executor executor/executor.cc \
	-O2 -pthread -Wall -Werror -Wparentheses -Wunused-const-variable -Wframe-larger-than=16384 -Wno-stringop-overflow -Wno-array-bounds -Wno-format-overflow -Wno-unused-but-set-variable -Wno-unused-command-line-argument -static-pie -std=c++17 -I. -Iexecutor/_include   -DGOOS_linux=1 -DGOARCH_arm64=1 \
	-DHOSTGOOS_linux=1 -DGIT_REVISION=\"c06e8995d711b5a8d8fbd771826fcbfdac6f110f\"
/usr/lib/gcc-cross/aarch64-linux-gnu/14/../../../../aarch64-linux-gnu/bin/ld: /tmp/ccHZ4d27.o: in function `Connection::Connect(char const*, char const*)':
executor.cc:(.text._ZN10Connection7ConnectEPKcS1_[_ZN10Connection7ConnectEPKcS1_]+0x2ec): warning: Using 'gethostbyname' in statically linked applications requires at runtime the shared libraries from the glibc version used for linking



Tested on:

commit:         1e0a8362 Merge branches 'for-next/core' and 'for-next/..
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
kernel config:  https://syzkaller.appspot.com/x/.config?x=1aef92cd87e68b9f
dashboard link: https://syzkaller.appspot.com/bug?extid=14b6d57fb728e27ce23c
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
userspace arch: arm64
patch:          https://syzkaller.appspot.com/x/patch.diff?x=1242ca02580000