Re: [syzbot] [bluetooth?] KASAN: slab-use-after-free Read in l2cap_sock_new_connection_cb

[syzbot <syzbot+cdae834448ec8c3602fe@syzkaller.appspotmail.com>]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
general protection fault in lock_sock_nested

 </TASK>
kobject: kobject_add_internal failed for hci3:201 with -EEXIST, don't try to register things with the same name in the same directory.
Bluetooth: hci3: failed to register connection device
Oops: general protection fault, probably for non-canonical address 0xdffffc000000006b: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000358-0x000000000000035f]
CPU: 1 UID: 0 PID: 5116 Comm: kworker/u9:1 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Workqueue: hci3 hci_rx_work
RIP: 0010:kasan_byte_accessible+0x12/0x30 mm/kasan/generic.c:210
Code: 0f 1f 84 00 00 00 00 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 0f 1f 40 d6 48 c1 ef 03 48 b8 00 00 00 00 00 fc ff df <0f> b6 04 07 3c 08 0f 92 c0 c3 cc cc cc cc cc 66 66 66 66 66 66 2e
RSP: 0018:ffffc900106072e8 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: ffffffff889d1fbe RCX: 562ba08c8e500400
RDX: 0000000000000000 RSI: ffffffff889d1fbe RDI: 000000000000006b
RBP: ffffffff89ca6065 R08: 0000000000000001 R09: 0000000000000000
R10: dffffc0000000000 R11: ffffffff89ca6020 R12: 0000000000000000
R13: 0000000000000358 R14: 0000000000000358 R15: 0000000000000001
FS:  0000000000000000(0000) GS:ffff888126ef4000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000555572fa15c8 CR3: 000000000d3a6000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 __kasan_check_byte+0x12/0x40 mm/kasan/common.c:579
 kasan_check_byte include/linux/kasan.h:401 [inline]
 lock_acquire+0x8d/0x360 kernel/locking/lockdep.c:5842
 lock_sock_nested+0x3e/0x130 net/core/sock.c:3720
 lock_sock include/net/sock.h:1679 [inline]
 l2cap_sock_ready_cb+0x45/0x140 net/bluetooth/l2cap_sock.c:1680
 l2cap_chan_ready net/bluetooth/l2cap_core.c:1264 [inline]
 l2cap_le_start+0xb0d/0x13b0 net/bluetooth/l2cap_core.c:1376
 l2cap_conn_ready net/bluetooth/l2cap_core.c:1629 [inline]
 l2cap_connect_cfm+0x6be/0x1040 net/bluetooth/l2cap_core.c:7305
 hci_connect_cfm+0x95/0x140 include/net/bluetooth/hci_core.h:2107
 le_conn_complete_evt+0xfb8/0x1500 net/bluetooth/hci_event.c:5799
 hci_le_conn_complete_evt+0x187/0x450 net/bluetooth/hci_event.c:5825
 hci_event_func net/bluetooth/hci_event.c:7586 [inline]
 hci_event_packet+0x78f/0x1200 net/bluetooth/hci_event.c:7643
 hci_rx_work+0x46a/0xe80 net/bluetooth/hci_core.c:4099
 process_one_work kernel/workqueue.c:3263 [inline]
 process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3346
 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3427
 kthread+0x711/0x8a0 kernel/kthread.c:463
 ret_from_fork+0x4bc/0x870 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:kasan_byte_accessible+0x12/0x30 mm/kasan/generic.c:210
Code: 0f 1f 84 00 00 00 00 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 0f 1f 40 d6 48 c1 ef 03 48 b8 00 00 00 00 00 fc ff df <0f> b6 04 07 3c 08 0f 92 c0 c3 cc cc cc cc cc 66 66 66 66 66 66 2e
RSP: 0018:ffffc900106072e8 EFLAGS: 00010202
RAX: dffffc0000000000 RBX: ffffffff889d1fbe RCX: 562ba08c8e500400
RDX: 0000000000000000 RSI: ffffffff889d1fbe RDI: 000000000000006b
RBP: ffffffff89ca6065 R08: 0000000000000001 R09: 0000000000000000
R10: dffffc0000000000 R11: ffffffff89ca6020 R12: 0000000000000000
R13: 0000000000000358 R14: 0000000000000358 R15: 0000000000000001
FS:  0000000000000000(0000) GS:ffff888126ef4000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000555572fa15c8 CR3: 000000000d3a6000 CR4: 00000000003526f0
----------------
Code disassembly (best guess):
   0:	0f 1f 84 00 00 00 00 	nopl   0x0(%rax,%rax,1)
   7:	00
   8:	90                   	nop
   9:	90                   	nop
   a:	90                   	nop
   b:	90                   	nop
   c:	90                   	nop
   d:	90                   	nop
   e:	90                   	nop
   f:	90                   	nop
  10:	90                   	nop
  11:	90                   	nop
  12:	90                   	nop
  13:	90                   	nop
  14:	90                   	nop
  15:	90                   	nop
  16:	90                   	nop
  17:	90                   	nop
  18:	0f 1f 40 d6          	nopl   -0x2a(%rax)
  1c:	48 c1 ef 03          	shr    $0x3,%rdi
  20:	48 b8 00 00 00 00 00 	movabs $0xdffffc0000000000,%rax
  27:	fc ff df
* 2a:	0f b6 04 07          	movzbl (%rdi,%rax,1),%eax <-- trapping instruction
  2e:	3c 08                	cmp    $0x8,%al
  30:	0f 92 c0             	setb   %al
  33:	c3                   	ret
  34:	cc                   	int3
  35:	cc                   	int3
  36:	cc                   	int3
  37:	cc                   	int3
  38:	cc                   	int3
  39:	66                   	data16
  3a:	66                   	data16
  3b:	66                   	data16
  3c:	66                   	data16
  3d:	66                   	data16
  3e:	66                   	data16
  3f:	2e                   	cs


Tested on:

commit:         ac3fd01e Linux 6.18-rc7
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10f578b4580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=38a0c4cddc846161
dashboard link: https://syzkaller.appspot.com/bug?extid=cdae834448ec8c3602fe
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
patch:          https://syzkaller.appspot.com/x/patch.diff?x=11e46e92580000