linux-kernel - Re: [PATCH 2/6] netlink: have netlink per-protocol bind function return an error code.

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Message-ID: <20140423013005.GB20182@madcap2.tricolour.ca>
Date:	Tue, 22 Apr 2014 21:30:05 -0400
From:	Richard Guy Briggs <rgb@...hat.com>
To:	David Miller <davem@...emloft.net>
Cc:	linux-audit@...hat.com, linux-kernel@...r.kernel.org,
	netdev@...r.kernel.org, selinux@...ho.nsa.gov,
	linux-security-module@...r.kernel.org, eparis@...hat.com,
	hadi@...atatu.com, sgrubb@...hat.com
Subject: Re: [PATCH 2/6] netlink: have netlink per-protocol bind function
 return an error code.

On 14/04/22, David Miller wrote:
> From: Richard Guy Briggs <rgb@...hat.com>
> Date: Fri, 18 Apr 2014 13:34:06 -0400
> 
> > @@ -1449,6 +1453,26 @@ static int netlink_bind(struct socket *sock, struct sockaddr *addr,
> >  	if (!nladdr->nl_groups && (nlk->groups == NULL || !(u32)nlk->groups[0]))
> >  		return 0;
> >  
> > +	if (nlk->netlink_bind && nladdr->nl_groups) {
> > +		int i;
> > +
> > +		for (i = 0; i < nlk->ngroups; i++) {
> > +			int undo;
> > +
> > +			if (!test_bit(i, (long unsigned int *)&nladdr->nl_groups))
> > +				continue;
> > +			err = nlk->netlink_bind(i);
> > +			if (!err)
> > +				continue;
> > +			if (!nlk->portid)
> > +				netlink_remove(sk);
> > +			for (undo = 0; undo < i; undo++)
> > +				if (nlk->netlink_unbind)
> > +					nlk->netlink_unbind(undo);
> > +			return err;
> > +		}
> > +	}
> > +
> 
> It took me a while to figure out why you need to do the netlink_remove() in
> the error path.
> 
> I think it's really asking for trouble to allow the socket to have temporary
> visibility if we end up signalling an error.

The risk seems small, but I agree it is sloppy.

> It seems safest if we only do the autobind/insert once we are absolutely
> certain that the bind() will fully succeed.  This means that you have to
> do this bind validation loop before autobind/insert.

Ok, done.  This revision ends up being a bit cleaner than the previous
one because I've refactored out the unbind loop into netlink_unbind()
due to it needing to be called if the netlink_insert/autobind() fails as
well.  In the factorization process I noticed that unrequested groups
were being unnecessarily unbound.  It also provoked assigning the var
"groups" from "nladdr->nl_groups" making things easier to read.

> Please make this change and resubmit this series, thanks.

Compiled and tested.  New patchset to follow.

- RGB

--
Richard Guy Briggs <rbriggs@...hat.com>
Senior Software Engineer, Kernel Security, AMER ENG Base Operating Systems, Red Hat
Remote, Ottawa, Canada
Voice: +1.647.777.2635, Internal: (81) 32635, Alt: +1.613.693.0684x3545
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