linux-kernel - Re: [PATCH 0/3] fs: reduce export usage of kerne

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Date:   Fri, 05 Jun 2020 14:37:18 -0400
From:   Mimi Zohar <zohar@...ux.ibm.com>
To:     Scott Branden <scott.branden@...adcom.com>,
        Kees Cook <keescook@...omium.org>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Luis Chamberlain <mcgrof@...nel.org>, viro@...iv.linux.org.uk,
        gregkh@...uxfoundation.org, rafael@...nel.org,
        ebiederm@...ssion.com, jeyu@...nel.org, jmorris@...ei.org,
        paul@...l-moore.com, stephen.smalley.work@...il.com,
        eparis@...isplace.org, nayna@...ux.ibm.com,
        dan.carpenter@...cle.com, skhan@...uxfoundation.org,
        geert@...ux-m68k.org, tglx@...utronix.de, bauerman@...ux.ibm.com,
        dhowells@...hat.com, linux-integrity@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, kexec@...ts.infradead.org,
        linux-security-module@...r.kernel.org, selinux@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/3] fs: reduce export usage of kerne_read*() calls

On Fri, 2020-06-05 at 11:15 -0700, Scott Branden wrote:
> Hi Mimi,
> 
> On 2020-05-23 7:52 p.m., Mimi Zohar wrote:
> > Scott, the change should be straight forward.  The additional patch
> > needs to:
> > - define a new kernel_read_file_id enumeration, like
> > FIRMWARE_PARTIAL_READ.
> > - Currently ima_read_file() has a comment about pre-allocated firmware
> > buffers.  Update ima_read_file() to call process_measurement() for the
> > new enumeration FIRMWARE_PARTIAL_READ and update ima_post_read_file()
> > to return immediately.
> Should this be what is in ima_read_file?
> {
>      enum ima_hooks func;
>      u32 secid;

Please don't remove the existing comment.

>      if (read_id != READING_FIRMWARE_PARTIAL_READ)
>          return 0;
> 
>      if (!file) { /* should never happen */
>          if (ima_appraise & IMA_APPRAISE_ENFORCE)
>              return -EACCES;
>          return 0;
>      }

This checks for any IMA appraise rule.  You want to enforce firmware
signature checking only if there is a firmware appraise rule.  Refer
to ima_post_read_file().

>      security_task_getsecid(current, &secid);
>      return process_measurement(file, current_cred(), secid, NULL,
>                     0, MAY_READ, FILE_CHECK);

The read_idmap enumeration should be updated similar to the other
firmware.  Keep the code generic.  Refer to ima_post_read_file().
 func will be defined as FIRMWARE_CHECK.

thanks,

Mimi