Re: ipv4: Use standard iovec primitive in raw_probe_proto_opt

[David Miller <davem@davemloft.net>]

From: Herbert Xu <herbert@gondor.apana.org.au>
Date: Thu, 6 Nov 2014 14:46:29 +0800

> On Thu, Nov 06, 2014 at 06:43:18AM +0000, Al Viro wrote:
>> On Thu, Nov 06, 2014 at 01:50:23PM +0800, Herbert Xu wrote:
>> > +	/* We only need the first two bytes. */
>> > +	err = memcpy_fromiovecend((void *)&icmph, msg->msg_iov, 0, 2);
>> > +	if (err)
>> > +		return err;
>> > +
>> > +	fl4->fl4_icmp_type = icmph.type;
>> > +	fl4->fl4_icmp_code = icmph.code;
>> 
>> That's more readable, but that exposes another problem in there - we read
>> the same piece of userland data twice, with no promise whatsoever that we'll
>> get the same value both times...
> 
> Sure, but you have to be root anyway to write to raw sockets.
> 
> Patches are welcome :)

I'd agree with this root-only argument maybe 15 years ago, but with
containers and stuff like that we want to prevent root X from messing
up the machine for root Y.

This is a recurring topic, and I'd strongly like to avoid adding new
ways that these kinds of problems can happen.

For example, I'm still on the hook to address the AF_NETLINK mmap TX
code, which has a similarly abusable issue.