Re: [syzbot] [bluetooth?] KASAN: slab-use-after-free Read in l2cap_send_cmd

[syzbot <syzbot+31c2f641b850a348a734@syzkaller.appspotmail.com>]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
general protection fault in l2cap_send_cmd

Bluetooth: Wrong link type (-22)
Oops: general protection fault, probably for non-canonical address 0xdffffc0000000064: 0000 [#1] PREEMPT SMP KASAN PTI
KASAN: null-ptr-deref in range [0x0000000000000320-0x0000000000000327]
CPU: 0 UID: 0 PID: 8403 Comm: kworker/u9:10 Not tainted 6.13.0-rc7-syzkaller-g9bffa1ad25b8 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
Workqueue: hci4 hci_rx_work

RIP: 0010:l2cap_send_cmd+0x563/0x8d0 net/bluetooth/l2cap_core.c:964
Code: fc ff df 80 3c 08 00 74 08 48 89 df e8 f6 54 42 f7 bd 22 03 00 00 48 03 2b 48 89 e8 48 c1 e8 03 48 b9 00 00 00 00 00 fc ff df <0f> b6 04 08 84 c0 0f 85 11 01 00 00 0f b6 5d 00 89 de 83 e6 40 31
RSP: 0018:ffffc9000557f378 EFLAGS: 00010202

RAX: 0000000000000064 RBX: ffff88801eb23c78 RCX: dffffc0000000000
RDX: 0000000000000000 RSI: 0000000000000008 RDI: ffff888034724000
RBP: 0000000000000322 R08: ffffffff8ac395c4 R09: 0000000000000000
R10: dffffc0000000000 R11: ffffed100f588363 R12: ffff888034724000
R13: ffff888034724010 R14: ffff88801eb22c80 R15: ffff888063932140
FS:  0000000000000000(0000) GS:ffff8880b8600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055558b7da5c8 CR3: 000000002974a000 CR4: 00000000003526f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 l2cap_sig_send_rej net/bluetooth/l2cap_core.c:5502 [inline]
 l2cap_sig_channel net/bluetooth/l2cap_core.c:5538 [inline]
 l2cap_recv_frame+0x221f/0x10db0 net/bluetooth/l2cap_core.c:6817
 hci_acldata_packet net/bluetooth/hci_core.c:3797 [inline]
 hci_rx_work+0x508/0xdb0 net/bluetooth/hci_core.c:4040
 process_one_work kernel/workqueue.c:3236 [inline]
 process_scheduled_works+0xa66/0x1840 kernel/workqueue.c:3317
 worker_thread+0x870/0xd30 kernel/workqueue.c:3398
 kthread+0x2f0/0x390 kernel/kthread.c:389
 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:l2cap_send_cmd+0x563/0x8d0 net/bluetooth/l2cap_core.c:964
Code: fc ff df 80 3c 08 00 74 08 48 89 df e8 f6 54 42 f7 bd 22 03 00 00 48 03 2b 48 89 e8 48 c1 e8 03 48 b9 00 00 00 00 00 fc ff df <0f> b6 04 08 84 c0 0f 85 11 01 00 00 0f b6 5d 00 89 de 83 e6 40 31
RSP: 0018:ffffc9000557f378 EFLAGS: 00010202

RAX: 0000000000000064 RBX: ffff88801eb23c78 RCX: dffffc0000000000
RDX: 0000000000000000 RSI: 0000000000000008 RDI: ffff888034724000
----------------
Code disassembly (best guess), 2 bytes skipped:
   0:	df 80 3c 08 00 74    	filds  0x7400083c(%rax)
   6:	08 48 89             	or     %cl,-0x77(%rax)
   9:	df e8                	fucomip %st(0),%st
   b:	f6 54 42 f7          	notb   -0x9(%rdx,%rax,2)
   f:	bd 22 03 00 00       	mov    $0x322,%ebp
  14:	48 03 2b             	add    (%rbx),%rbp
  17:	48 89 e8             	mov    %rbp,%rax
  1a:	48 c1 e8 03          	shr    $0x3,%rax
  1e:	48 b9 00 00 00 00 00 	movabs $0xdffffc0000000000,%rcx
  25:	fc ff df
* 28:	0f b6 04 08          	movzbl (%rax,%rcx,1),%eax <-- trapping instruction
  2c:	84 c0                	test   %al,%al
  2e:	0f 85 11 01 00 00    	jne    0x145
  34:	0f b6 5d 00          	movzbl 0x0(%rbp),%ebx
  38:	89 de                	mov    %ebx,%esi
  3a:	83 e6 40             	and    $0x40,%esi
  3d:	31                   	.byte 0x31


Tested on:

commit:         9bffa1ad Merge tag 'drm-fixes-2025-01-17' of https://g..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16139fc4580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=aadf89e2f6db86cc
dashboard link: https://syzkaller.appspot.com/bug?extid=31c2f641b850a348a734
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

Note: no patches were applied.