netdev - Re: [WTF?] random test in netlink

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Message-Id: <20141212.213313.1419808296502891420.davem@davemloft.net>
Date:	Fri, 12 Dec 2014 21:33:13 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	viro@...IV.linux.org.uk
Cc:	kaber@...sh.net, netdev@...r.kernel.org
Subject: Re: [WTF?] random test in netlink_sendmsg()

From: Al Viro <viro@...IV.linux.org.uk>
Date: Sat, 13 Dec 2014 01:54:15 +0000

> On Fri, Dec 12, 2014 at 08:07:58PM -0500, David Miller wrote:
>> From: Al Viro <viro@...IV.linux.org.uk>
>> Date: Fri, 12 Dec 2014 21:32:43 +0000
>> 
>> > What do we want sendmsg(fd, &msg, 0) to do when fd is AF_NETLINK socket
>> > that had setsockopt(fd, SOL_NETLINK, NETLINK_TX_RING, ...) successfully done
>> > to it and msg.msg_iovlen is 0?
>> 
>> We had a similar issue with msg_name/msg_namelen and we ended up saying
>> that if msg_namelen is zero then we force msg_name to NULL.
> 
> Hmm...  The thing is, there might be legitimate users with empty payload,
> making this call for the sake of SCM_CREDENTIALS.  IOW, what should happen
> if we have
> 	msg_iovlen = 0
> 	msg_iov = <anything>
> 	msg_control = &cmsg
> 	msg_controllen = cmsg_len
> Sure, both paths will pass creds, but what about the payload?  And the number
> of datagram actually transmitted, for that matter?

Ok, so we just adjust the AF_PACKET check to test msg_iovlen==1 as
well, and that takes care of that case.

Right?
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