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From: Coiby Xu <coiby.xu@gmail.com>
To: syzkaller-bugs@googlegroups.com
Cc: linux-kernel-mentees@lists.linuxfoundation.org
Subject: [Linux-kernel-mentees] How does syzkaller manage to create Bluetooth connections in a VM which doesn't have a Bluetooth device
Date: Fri, 4 Sep 2020 22:19:54 +0800	[thread overview]
Message-ID: <20200904141954.uhfxllwykxshtisu@Rk> (raw)

Hi,

I have been trying to fix this issue [1] found by syzbot. I notice the
extracted syzkaller reproducer could connect to another Bluetooth device
successfully because l2cap_chan_connect successfully returns.

// net/Bluetooth/l2cap_sock.c
static int l2cap_sock_connect(struct socket *sock, struct sockaddr *addr,
			      int alen, int flags)
{
	err = l2cap_chan_connect(chan, la.l2_psm, __le16_to_cpu(la.l2_cid),
				 &la.l2_bdaddr, la.l2_bdaddr_type);
}

However, if I use syz-prog2c to convert the syzkaller reproducer to a
C reproducer, the C reproducer could never make a socket connect call
successfully. So how does syzkaller manage to create Bluetooth connections
for the sykaller reproducer? I've understood why this issue [1] occurs
but haven't figured out how it occurs, i.e., what is the subtle race
condition. So I want to write a C reproducer to experiment on it.

[1] INFO: trying to register non-static key in l2cap_chan_del: https://syzkaller.appspot.com/bug?id=aca31fd1ef0cbf898bd37115e2c4c66fa37f4a20

--
Best regards,
Coiby
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             reply	other threads:[~2020-09-04 14:20 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-04 14:19 Coiby Xu [this message]
2020-09-08  7:16 ` Dmitry Vyukov via Linux-kernel-mentees

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