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

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Date:   Fri, 22 Dec 2017 22:03:48 -0600
From:   "Serge E. Hallyn" <serge@...lyn.com>
To:     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>,
        Mimi Zohar <zohar@...ux.vnet.ibm.com>,
        "Serge E. Hallyn" <serge@...lyn.com>
Subject: Re: [PATCH 11/11] evm: Don't update hmacs in user ns mounts

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?

> 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