linux-kernel - Re: [PATCH v2] ima: drop vla in ima_audit

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Message-Id: <1520546740.3605.124.camel@linux.vnet.ibm.com>
Date:   Thu, 08 Mar 2018 17:05:40 -0500
From:   Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:     Tycho Andersen <tycho@...ho.ws>
Cc:     Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
        linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH v2] ima: drop vla in ima_audit_measurement()

On Thu, 2018-03-08 at 14:45 -0700, Tycho Andersen wrote:
> Hi Mimi,
> 
> On Thu, Mar 08, 2018 at 03:36:14PM -0500, Mimi Zohar wrote:
> > On Thu, 2018-03-08 at 13:23 -0700, Tycho Andersen wrote:
> > 
> > >  /*
> > > diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
> > > index 2cfb0c714967..356faae6f09c 100644
> > > --- a/security/integrity/ima/ima_main.c
> > > +++ b/security/integrity/ima/ima_main.c
> > > @@ -288,8 +288,11 @@ static int process_measurement(struct file *file, char *buf, loff_t size,
> > >  					      xattr_value, xattr_len, opened);
> > >  		inode_unlock(inode);
> > >  	}
> > > -	if (action & IMA_AUDIT)
> > > -		ima_audit_measurement(iint, pathname);
> > > +	if (action & IMA_AUDIT) {
> > > +		rc = ima_audit_measurement(iint, pathname);
> > > +		if (rc < 0)
> > > +			goto out_locked;
> > > +	}
> > > 
> > >  	if ((file->f_flags & O_DIRECT) && (iint->flags & IMA_PERMIT_DIRECTIO))
> > >  		rc = 0;
> > 
> > Only when IMA-appraisal is enforcing file data integrity should
> > process_measurement() ever fail.  Other errors can be logged/audited.
> 
> Ok, so previously in ima_audit_measurement() when allocation failed,
> there was nothing logged. If we just keep this behavior like below,
> does that look good?

Before the IMA locking change that were just upstreamed, there were
problems with measuring/appraising files that were opened with the
O_DIRECT flag.  Unless the IMA policy specified permit_directio, the
measurement/appraisal failed.  With the new locking, opening files
with the O_DIRECTIO flag shouldn't be a problem.  It just needs to be
fully tested before removing this code.

On failure, the code below tests the ima_audit_measurement() result
and skips the IMA_PERMIT_DIRECTIO test.  Unless I'm missing something,
I don't see the point.

Mimi


> Thanks!
> 
> Tycho
> 
> diff --git a/security/integrity/ima/ima_main.c b/security/integrity/ima/ima_main.c
> index 356faae6f09c..4e699bc7adc5 100644
> --- a/security/integrity/ima/ima_main.c
> +++ b/security/integrity/ima/ima_main.c
> @@ -289,9 +289,13 @@ static int process_measurement(struct file *file, char *buf, loff_t size,
>  		inode_unlock(inode);
>  	}
>  	if (action & IMA_AUDIT) {
> -		rc = ima_audit_measurement(iint, pathname);
> -		if (rc < 0)
> +		int ret;
> +
> +		ret = ima_audit_measurement(iint, pathname);
> +		if (ret < 0 && ima_appraise & IMA_APPRAISE_ENFORCE) {
> +			rc = ret;
>  			goto out_locked;
> +		}
>  	}
> 
>  	if ((file->f_flags & O_DIRECT) && (iint->flags & IMA_PERMIT_DIRECTIO))
>