linux-kernel - Re: [PATCH ghak109 V1] audit: link integrity evm_write

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Date:   Tue, 26 Mar 2019 13:42:52 -0400
From:   Richard Guy Briggs <rgb@...hat.com>
To:     Mimi Zohar <zohar@...ux.ibm.com>
Cc:     Steve Grubb <sgrubb@...hat.com>, Paul Moore <paul@...l-moore.com>,
        linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        Linux-Audit Mailing List <linux-audit@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>, omosnace@...hat.com,
        Eric Paris <eparis@...isplace.org>,
        Serge Hallyn <serge@...lyn.com>, mjg59@...gle.com
Subject: Re: [PATCH ghak109 V1] audit: link integrity evm_write_xattrs record
 to syscall event

On 2019-03-26 12:14, Richard Guy Briggs wrote:
> On 2019-03-26 11:29, Mimi Zohar wrote:
> > On Tue, 2019-03-26 at 11:22 -0400, Steve Grubb wrote:
> > 
> > > > > > --- a/security/integrity/evm/evm_secfs.c
> > > > > > +++ b/security/integrity/evm/evm_secfs.c
> > > > > > @@ -192,7 +192,8 @@ static ssize_t evm_write_xattrs(struct file *file,
> > > > > > const char __user *buf,> > 
> > > > > >         if (count > XATTR_NAME_MAX)
> > > > > >         
> > > > > >                 return -E2BIG;
> > > > > > 
> > > > > > -       ab = audit_log_start(NULL, GFP_KERNEL,
> > > > > > AUDIT_INTEGRITY_EVM_XATTR);
> > > > > > +       ab = audit_log_start(audit_context(), GFP_KERNEL,
> > > > > > +                            AUDIT_INTEGRITY_EVM_XATTR);
> > > > > 
> > > > > This part is fine.
> > > > > 
> > > > > >         if (!ab)
> > > > > >         
> > > > > >                 return -ENOMEM;
> > > > > > 
> > > > > > @@ -222,7 +223,7 @@ static ssize_t evm_write_xattrs(struct file *file,
> > > > > > const char __user *buf,> > 
> > > > > >                 inode_lock(inode);
> > > > > >                 err = simple_setattr(evm_xattrs, &newattrs);
> > > > > >                 inode_unlock(inode);
> > > > > > 
> > > > > > -               audit_log_format(ab, "locked");
> > > > > > +               audit_log_format(ab, "xattr=(locked)");
> > > > > 
> > > > > Two things come to mind:
> > > > > 
> > > > > * While we can clearly trust the string above, should we be logging
> > > > > the xattr field value as an untrusted string so it is consistent with
> > > > > how we record other xattr names?
> > > > 
> > > > That would be a question for Steve.
> > > 
> > > All fields with the same name must be represented the same way. If one 
> > > instance is untrusted, every instance of the same keyword must be untrusted.
> > 
> > Normal case:
> >        audit_log_format(ab, "xattr=");
> >        audit_log_untrustedstring(ab, xattr->name);
> > 
> > Ok, so the above audit_log_format() call should be replaced with
> >  audit_log_untrustedstring().
> 
> Ok, so I think we can agree on "audit_log_untrustedstring(ab,
> "xattr=.");" and simpler yet just print the contents regardless and not
> special case this print.  V2 coming...

Ok, what I typed above wasn't quite what I intended...  This is what I
meant:

	audit_log_format(ab, "xattr=");
	audit_log_untrustedstring(ab, ".");

But, I'll just move the normal case above the "." locking detection and
log all cases the same way.

> > Mimi
> 
> - RGB

- RGB

--
Richard Guy Briggs <rgb@...hat.com>
Sr. S/W Engineer, Kernel Security, Base Operating Systems
Remote, Ottawa, Red Hat Canada
IRC: rgb, SunRaycer
Voice: +1.647.777.2635, Internal: (81) 32635