On 2017-05-24 19:36, Pablo Neira Ayuso wrote:
> On Thu, May 18, 2017 at 01:21:49PM -0400, Richard Guy Briggs wrote:
> > There were syscall events unsolicited by any audit rule caused by a missing
> > !audit_dummy_context() check before creating an
> > iptables/ip6tables/arptables/ebtables NETFILTER_CFG record. Check
> > !audit_dummy_context() before creating the NETFILTER_CFG record.
> >
> > The vast majority of observed unaccompanied records are caused by the fedora
> > default rule: "-a never,task" and the occasional early startup one is I believe
> > caused by the iptables filter table module hard linked into the kernel rather
> > than a loadable module. The !audit_dummy_context() check above should avoid
> > them. Audit only when there is an existing syscall audit rule, otherwise issue
> > a standalone record only on table modification rather than empty table
> > creation.
> >
> > Add subject attributes to the new standalone NETFILTER_CFGSOLO record using
> > a newly exported audit_log_task().
>
> This new NETFILTER_CFGSOLO looks like audit infra is missing some way
> to export a revision / context to userspace? It's duplicating quite a
> bit of the code from what I can see in this patch.
Interesting you brought that up. I did another revision that stores
this information in a struct audit_context and greatly simplifies the
code in netfilter and re-uses code in audit itself, which may be a
better way to go, but that idea needed to settle a bit more before
seeing peer review.
>
I'm also having doubts about two record types.
> > diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
> > index 0714a66..8bee3f5 100644
> > --- a/include/uapi/linux/audit.h
> > +++ b/include/uapi/linux/audit.h
> > @@ -112,6 +112,7 @@
> > #define AUDIT_FEATURE_CHANGE 1328 /* audit log listing feature changes */
> > #define AUDIT_REPLACE 1329 /* Replace auditd if this packet unanswerd */
> > #define AUDIT_KERN_MODULE 1330 /* Kernel Module events */
> > +#define AUDIT_NETFILTER_CFGSOLO 1331 /* Netfilter chain modifications standalone */
> >
> > #define AUDIT_AVC 1400 /* SE Linux avc denial or grant */
> > #define AUDIT_SELINUX_ERR 1401 /* Internal SE Linux Errors */
> > diff --git a/kernel/auditsc.c b/kernel/auditsc.c
> > index b2dcbe6..8ac38e6 100644
> > --- a/kernel/auditsc.c
> > +++ b/kernel/auditsc.c
> > @@ -2383,7 +2383,7 @@ void __audit_log_kern_module(char *name)
> > context->type = AUDIT_KERN_MODULE;
> > }
> >
> > -static void audit_log_task(struct audit_buffer *ab)
> > +void audit_log_task(struct audit_buffer *ab)
> > {
> > kuid_t auid, uid;
> > kgid_t gid;
> > @@ -2404,6 +2404,7 @@ static void audit_log_task(struct audit_buffer *ab)
> > audit_log_untrustedstring(ab, get_task_comm(comm, current));
> > audit_log_d_path_exe(ab, current->mm);
> > }
> > +EXPORT_SYMBOL_GPL(audit_log_task);
> >
> > /**
> > * audit_core_dumps - record information about processes that end abnormally
> > diff --git a/net/bridge/netfilter/ebtables.c b/net/bridge/netfilter/ebtables.c
> > index 13d7fe2..743f9e6 100644
> > --- a/net/bridge/netfilter/ebtables.c
> > +++ b/net/bridge/netfilter/ebtables.c
> > @@ -1071,12 +1071,25 @@ static int do_replace_finish(struct net *net, struct ebt_replace *repl,
> > if (audit_enabled) {
> > struct audit_buffer *ab;
> >
> > - ab = audit_log_start(current->audit_context, GFP_KERNEL,
> > - AUDIT_NETFILTER_CFG);
> > - if (ab) {
> > - audit_log_format(ab, "table=%s family=%u entries=%u",
> > - repl->name, AF_BRIDGE, repl->nentries);
> > - audit_log_end(ab);
> > + if(!audit_dummy_context()) {
> > + ab = audit_log_start(current->audit_context, GFP_KERNEL,
> > + AUDIT_NETFILTER_CFG);
> > + if (ab) {
> > + audit_log_format(ab, "family=%u table=%s entries=%u",
> > + AF_BRIDGE, repl->name,
> > + repl->nentries);
> > + audit_log_end(ab);
> > + }
> > + } else if(repl->nentries) {
> > + ab = audit_log_start(NULL, GFP_KERNEL,
> > + AUDIT_NETFILTER_CFGSOLO);
> > + if (ab) {
> > + audit_log_task(ab);
> > + audit_log_format(ab, " family=%u table=%s entries=%u",
> > + AF_BRIDGE, repl->name,
> > + repl->nentries);
> > + audit_log_end(ab);
> > + }
>
> If you have no other way, probably it is a good idea to wrap this code
> around a function, eg. ebt_audit_replace_finish() ?
Yes, sending the values I need into the audit subsystem to avoid
exposing some bits of audit did come to mind. And it would bring 6
lines here down to one instead of adding 19.
- RGB
--
Richard Guy Briggs <rgb@xxxxxxxxxx>
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
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