linux-kernel - Re: [syzbot] WARNING: refcount bug in l2cap_chan

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Date:   Sat, 14 May 2022 22:24:10 -0700
From:   syzbot <syzbot+fd86a41b17a416a37a75@...kaller.appspotmail.com>
To:     hdanton@...a.com, linux-kernel@...r.kernel.org,
        syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] WARNING: refcount bug in l2cap_chan_hold

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
WARNING: refcount bug in l2cap_chan_hold

------------[ cut here ]------------
refcount_t: addition on 0; use-after-free.
WARNING: CPU: 3 PID: 3688 at lib/refcount.c:25 refcount_warn_saturate+0x169/0x1e0 lib/refcount.c:25
Modules linked in:
CPU: 3 PID: 3688 Comm: kworker/u19:2 Not tainted 5.18.0-rc6-syzkaller-00007-g9be9ed2612b5-dirty #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.14.0-2 04/01/2014
Workqueue: hci0 hci_rx_work
RIP: 0010:refcount_warn_saturate+0x169/0x1e0 lib/refcount.c:25
Code: 09 31 ff 89 de e8 97 44 81 fd 84 db 0f 85 36 ff ff ff e8 aa 40 81 fd 48 c7 c7 80 61 26 8a c6 05 0f 00 ad 09 01 e8 e7 f5 30 05 <0f> 0b e9 17 ff ff ff e8 8b 40 81 fd 0f b6 1d f4 ff ac 09 31 ff 89
RSP: 0018:ffffc90002ef7960 EFLAGS: 00010282
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: ffff888021eb8080 RSI: ffffffff815f4a18 RDI: fffff520005def1e
RBP: 0000000000000002 R08: 0000000000000000 R09: 0000000000000000
R10: ffffffff815ef3ee R11: 0000000000000000 R12: ffff888022671000
R13: 0000000000000001 R14: 0000000000000000 R15: 0000000000000003
FS:  0000000000000000(0000) GS:ffff88802cd00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000555555842708 CR3: 0000000019825000 CR4: 0000000000150ee0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <TASK>
 __refcount_add include/linux/refcount.h:199 [inline]
 __refcount_inc include/linux/refcount.h:250 [inline]
 refcount_inc include/linux/refcount.h:267 [inline]
 kref_get include/linux/kref.h:45 [inline]
 l2cap_chan_hold+0xff/0x120 net/bluetooth/l2cap_core.c:497
 l2cap_global_chan_by_psm+0x3b1/0x4a0 net/bluetooth/l2cap_core.c:1986
 l2cap_conless_channel net/bluetooth/l2cap_core.c:7611 [inline]
 l2cap_recv_frame+0x68d/0x8e60 net/bluetooth/l2cap_core.c:7681
 l2cap_recv_acldata+0xa96/0xc10 net/bluetooth/l2cap_core.c:8394
 hci_acldata_packet net/bluetooth/hci_core.c:3633 [inline]
 hci_rx_work+0x4d5/0xd60 net/bluetooth/hci_core.c:3824
 process_one_work+0x996/0x1610 kernel/workqueue.c:2289
 worker_thread+0x665/0x1080 kernel/workqueue.c:2436
 kthread+0x2e9/0x3a0 kernel/kthread.c:376
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:298
 </TASK>


Tested on:

commit:         9be9ed26 Merge tag 'platform-drivers-x86-v5.18-4' of g..
git tree:       https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/
console output: https://syzkaller.appspot.com/x/log.txt?x=1449db8ef00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=3afe599903e2c6b6
dashboard link: https://syzkaller.appspot.com/bug?extid=fd86a41b17a416a37a75
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
patch:          https://syzkaller.appspot.com/x/patch.diff?x=159a21f1f00000