linux-kernel - Re: Hundreds of null PATH records for *init

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Date:   Tue, 28 Feb 2017 23:15:38 -0500
From:   Steve Grubb <sgrubb@...hat.com>
To:     Richard Guy Briggs <rgb@...hat.com>
Cc:     Linux-Audit Mailing List <linux-audit@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Eric Paris <eparis@...hat.com>, Paul Moore <pmoore@...hat.com>
Subject: Re: Hundreds of null PATH records for *init_module syscall audit logs

On Tuesday, February 28, 2017 10:37:04 PM EST Richard Guy Briggs wrote:
> Sorry, I forgot to include Cc: in this cover letter for context to the 4
> alt patches.
> 
> On 2017-02-28 22:15, Richard Guy Briggs wrote:
> > The background to this is:
> > 	https://github.com/linux-audit/audit-kernel/issues/8
> > 
> > In short, audit SYSCALL records for *init_module were occasionally
> > accompanied by hundreds to thousands of null PATH records.
> > 
> > I chatted with Al Viro and Eric Paris about this Friday afternoon and
> > they seemed to vaguely recall this issue and didn't have any solid
> > recommendations as to what was the right thing to do (other than the
> > same suggestion from both that I won't print here).
> > 
> > It was reproducible on a number of vintages of distributions with
> > default kernels, but triggering on very few of the many modules loaded
> > at boot time.  It was reproduced with fs-nfs4 and nfsv4 modules on
> > tracefs, but there are reports of it also happening with debugfs.  It
> > was triggering only in __audit_inode_child with a parent that was not
> > found in the task context's audit names_list.
> > 
> > I have four potential solutions listed in my order of preference and I'd
> > like to get some feedback about which one would be the most acceptable.

0.5 - Notice that we are in *init_module & delete_module and inhibit 
generation of any record type except SYSCALL and KERN_MODULE ? There are some 
classification routines for -F perms=wrxa that might be used to create a new 
class for loading/deleting modules that sets a flag that we use to suppress 
some record types.

> > 1 - In __audit_inode_child, return immedialy upon detecting TRACEFS and
> > 
> >     DEBUGFS (and potentially other filesystems identified, via s_magic).

XFS creates them too. Who knows what else.

-Steve

> > 2 - In __audit_inode_child, return after not finding the parent in that
> > 
> >     task context's audit names_list.
> > 
> > 3 - In __audit_inode_child, mark the parent and its child as "hidden"
> > 
> >     when the parent isn't found in that task context's audit names_list.
> >     This will still result in an "items=" count that does not match the
> >     number of accompanying PATH records for that SYSCALL record, which
> >     may upset userspace tools but would still indicate suppressed
> >     records.
> > 
> > 4 - In __audit_inode_child, when the parent isn't found, store the
> > 
> >     child's dentry in the child's (new or not) audit_names structure
> >     (properly refcounted with dget) and store the parent's dentry in its
> >     newly created audit_names structure (via dget_parent), then if the
> >     name isn't available at PATH record generation time, use that stored
> >     value (with dentry_path_raw and released with dput)
> >
> > Is there another more elegant solution that I've missed that catches
> > things before they get anywhere near audit_inode_child (called from
> > tracefs' notifiers)?
> > 
> > I'll thread onto this message tested patches for all four solutions.