Re: Hundreds of null PATH records for *init_module syscall audit logs
On Tue, Feb 28, 2017 at 10:37 PM, Richard Guy Briggs <rgb(a)redhat.com> 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'm no expert on the tracing system, but my understanding is that it
used to use debugfs but now prefers tracefs so perhaps depending on
the vintage of the kernel/userspace you will see it on either debugfs
or tracefs. I'm also guessing that module load order may have an
effect, maybe not.
> 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.
From an audit perspective, I'm generally not a fan of throwing
away
information, especially since solution #4 seems to provide some basic
PATH information. Although I guess the issue is do we care about
tracefs/debugfs PATH records?
> 1 - In __audit_inode_child, return immedialy upon detecting
TRACEFS and
> DEBUGFS (and potentially other filesystems identified, via s_magic).
If we decide we want to ignore debugfs/tracefs this may be the best solution.
> 2 - In __audit_inode_child, return after not finding the parent
in that
> task context's audit names_list.
This doesn't seem like the right answer.
> 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.
Similar to door #2, this doesn't seem right to me.
> 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)
This seems most in keeping with the spirit of audit.
> 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.
>
> - RGB
>
> --
> Richard Guy Briggs <rgb(a)redhat.com>
> Kernel Security Engineering, Base Operating Systems, Red Hat
> Remote, Ottawa, Canada
> Voice: +1.647.777.2635, Internal: (81) 32635
--
paul moore
www.paul-moore.com