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);
 
--