netdev - Re: [patch v2] net: heap overflow in __audit

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Date:	Wed, 27 Nov 2013 12:51:20 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Eric Wong <normalperson@...t.net>
Cc:	Dan Carpenter <dan.carpenter@...cle.com>,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	security@...nel.org,
	Jüri Aedla <juri.aedla@...il.com>,
	stable@...nel.org
Subject: Re: [patch v2] net: heap overflow in __audit_sockaddr()

On Wed, Nov 27, 2013 at 11:32:18AM +0000, Eric Wong wrote:
> Dan Carpenter <dan.carpenter@...cle.com> wrote:
> > --- a/net/socket.c
> > +++ b/net/socket.c
> > @@ -1964,6 +1964,16 @@ struct used_address {
> >  	unsigned int name_len;
> >  };
> >  
> > +static int copy_msghdr_from_user(struct msghdr *kmsg,
> > +				 struct msghdr __user *umsg)
> > +{
> > +	if (copy_from_user(kmsg, umsg, sizeof(struct msghdr)))
> > +		return -EFAULT;
> > +	if (kmsg->msg_namelen > sizeof(struct sockaddr_storage))
> > +		return -EINVAL;
> > +	return 0;
> 
> Crap, this seems to break Ruby trunk :x
> https://bugs.ruby-lang.org/issues/9124
> 
> I'm inclined to think Ruby is wrong to use a gigantic buffer, but this
> may also break some other existing userspace code.  I'm not sure what
> the best option since breaking userspace (even buggy userspace?) is not
> taken lightly.
> 
> Is there a different way to fix this in the kernel?
> 
> Note: this doesn't affect a stable release of Ruby, yet.

We have to clamp msg_namelen to max sizeof(struct sockaddr_storage).
The sendmsg handler will check msg_namelen again and error out correctly if
the size of msg_name is too short.

Greetings,

  Hannes

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