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

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Date:   Mon, 18 Dec 2017 08:28:05 -0800
From:   Santosh Shilimkar <santosh.shilimkar@...cle.com>
To:     syzbot 
        <bot+aaf54a8c644d559d34dedcf3126aac68a20c9e63@...kaller.appspotmail.com>,
        davem@...emloft.net, 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 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);