linux-kernel - Re: [PATCH 11/11] evm: Don't update hmacs in user ns mounts

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Message-Id: <1514092328.5221.116.camel@linux.vnet.ibm.com>
Date:   Sun, 24 Dec 2017 00:12:08 -0500
From:   Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:     "Serge E. Hallyn" <serge@...lyn.com>,
        Dongsu Park <dongsu@...volk.io>
Cc:     linux-kernel@...r.kernel.org,
        containers@...ts.linux-foundation.org,
        Alban Crequy <alban@...volk.io>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        Miklos Szeredi <mszeredi@...hat.com>,
        Seth Forshee <seth.forshee@...onical.com>,
        Sargun Dhillon <sargun@...gun.me>,
        linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        James Morris <james.l.morris@...cle.com>
Subject: Re: [PATCH 11/11] evm: Don't update hmacs in user ns mounts

Hi Serge,

On Fri, 2017-12-22 at 22:03 -0600, Serge E. Hallyn wrote:
> On Fri, Dec 22, 2017 at 03:32:35PM +0100, Dongsu Park wrote:
> > From: Seth Forshee <seth.forshee@...onical.com>
> > 
> > The kernel should not calculate new hmacs for mounts done by
> > non-root users. Update evm_calc_hmac_or_hash() to refuse to
> > calculate new hmacs for mounts for non-init user namespaces.
> > 
> > Cc: linux-integrity@...r.kernel.org
> > Cc: linux-security-module@...r.kernel.org
> > Cc: linux-kernel@...r.kernel.org
> > Cc: James Morris <james.l.morris@...cle.com>
> > Cc: Mimi Zohar <zohar@...ux.vnet.ibm.com>
> 
> Hi Mimi,
> 
> does this change seem sufficient to you?

I think this is the correct behavior in the context of fuse file
systems.  This patch, the "ima: define a new policy option named
force" patch, and an updated IMA policy should be upstreamed together.
 The cover letter should provide the motivation for these patches.

Mimi

> 
> > Cc: "Serge E. Hallyn" <serge@...lyn.com>
> > Signed-off-by: Seth Forshee <seth.forshee@...onical.com>
> > Signed-off-by: Dongsu Park <dongsu@...volk.io>
> > ---
> >  security/integrity/evm/evm_crypto.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/security/integrity/evm/evm_crypto.c b/security/integrity/evm/evm_crypto.c
> > index bcd64baf..729f4545 100644
> > --- a/security/integrity/evm/evm_crypto.c
> > +++ b/security/integrity/evm/evm_crypto.c
> > @@ -190,7 +190,8 @@ static int evm_calc_hmac_or_hash(struct dentry *dentry,
> >  	int error;
> >  	int size;
> >  
> > -	if (!(inode->i_opflags & IOP_XATTR))
> > +	if (!(inode->i_opflags & IOP_XATTR) ||
> > +	    inode->i_sb->s_user_ns != &init_user_ns)
> >  		return -EOPNOTSUPP;
> >  
> >  	desc = init_desc(type);
> > -- 
> > 2.13.6
>