linux-kernel - Re: [syzbot] kernel BUG at net/phonet/socket.c:LINE!

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Date:   Mon, 20 Dec 2021 00:09:47 +0300
From:   Pavel Skripkin <paskripkin@...il.com>
To:     syzbot <syzbot+2dc91e7fc3dea88b1e8a@...kaller.appspotmail.com>,
        courmisch@...il.com, davem@...emloft.net, kuba@...nel.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] kernel BUG at net/phonet/socket.c:LINE!

On 12/19/21 17:58, syzbot wrote:
> syzbot has found a reproducer for the following issue on:
> 
> HEAD commit:    60ec7fcfe768 qlcnic: potential dereference null pointer of..
> git tree:       net
> console output: https://syzkaller.appspot.com/x/log.txt?x=11b3505db00000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=fa556098924b78f0
> dashboard link: https://syzkaller.appspot.com/bug?extid=2dc91e7fc3dea88b1e8a
> compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=168791cdb00000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=14a0cbcdb00000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+2dc91e7fc3dea88b1e8a@...kaller.appspotmail.com
> 

This bug can be triggered via simple

sk = socket(AF_PHONET)
ioctl(sk, SIOCPNENABLEPIPE, 0)
connect(sk);


ioctl() sets sk->sk_state to TCP_SYN_SENT in pep_sock_enable() and then 
there is following check in pn_socket_bind():

	if (sk->sk_state != TCP_CLOSE || pn_port(pn->sobject)) {
		err = -EINVAL; /* attempt to rebind */
		goto out;
	}

Looks like "sk->sk_state != TCP_CLOSE" check is redundant and 
pn_port(pn->sobject) is unique flag, that socket is already binded.




With regards,
Pavel Skripkin