linux-kernel - Re: BUG: unable to handle kernel NULL pointer dereference in rds_send

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Message-ID: <b0a4bd8a-3b53-e187-b9e9-aa96baadd11d@oracle.com>
Date:   Mon, 18 Dec 2017 09:16:01 -0800
From:   Santosh Shilimkar <santosh.shilimkar@...cle.com>
To:     David Miller <davem@...emloft.net>
Cc:     bot+aaf54a8c644d559d34dedcf3126aac68a20c9e63@...kaller.appspotmail.com,
        linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org,
        netdev@...r.kernel.org, rds-devel@....oracle.com,
        syzkaller-bugs@...glegroups.com
Subject: Re: BUG: unable to handle kernel NULL pointer dereference in
 rds_send_xmit

On 12/18/2017 9:12 AM, David Miller wrote:
> From: Santosh Shilimkar <santosh.shilimkar@...cle.com>
> Date: Mon, 18 Dec 2017 08:28:05 -0800
> 
>> On 12/18/2017 12:43 AM, syzbot wrote:
>>> Hello,
>>> syzkaller hit the following crash on
>>> 6084b576dca2e898f5c101baef151f7bfdbb606d
>>> git://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/master
>>> compiler: gcc (GCC) 7.1.1 20170620
>>> .config is attached
>>> Raw console output is attached.
>>> Unfortunately, I don't have any reproducer for this bug yet.
>>> BUG: unable to handle kernel NULL pointer dereference at
>>> 0000000000000028
>>> program syz-executor6 is using a deprecated SCSI ioctl, please convert
>>> it to SG_IO
>>> IP: rds_send_xmit+0x80/0x930 net/rds/send.c:186
>>
>> Looks like another one tripping on empty transport. Mostly below
>> should
>> address it but we will test it if it does.
>>
>> diff --git a/net/rds/send.c b/net/rds/send.c
>> index 7244d2e..e2d0eaa 100644
>> --- a/net/rds/send.c
>> +++ b/net/rds/send.c
>> @@ -183,7 +183,7 @@ int rds_send_xmit(struct rds_conn_path *cp)
>>                  goto out;
>>          }
>>
>> -       if (conn->c_trans->xmit_path_prepare)
>> +       if (conn->c_trans && conn->c_trans->xmit_path_prepare)
>>                  conn->c_trans->xmit_path_prepare(cp);
> 
> We're seeming to accumulate a lot of checks like this, maybe there
> is a more general way to deal with this problem?
> 
Agree. Some of these additional transports hooks got added later
to specific transports which needs them. Will review this overall
and see if it can be addressed generically.

Regards,
Santosh