Re: [PATCH ghak124 v2] audit: log nftables configuration change events

[Richard Guy Briggs <rgb@redhat.com>]

On 2020-06-01 12:10, Paul Moore wrote:
> On Thu, May 28, 2020 at 9:44 PM Richard Guy Briggs <rgb@redhat.com> wrote:
> > iptables, ip6tables, arptables and ebtables table registration,
> > replacement and unregistration configuration events are logged for the
> > native (legacy) iptables setsockopt api, but not for the
> > nftables netlink api which is used by the nft-variant of iptables in
> > addition to nftables itself.
> >
> > Add calls to log the configuration actions in the nftables netlink api.
> >
> > This uses the same NETFILTER_CFG record format but overloads the table
> > field.
> >
> >   type=NETFILTER_CFG msg=audit(2020-05-28 17:46:41.878:162) : table=?:0;?:0 family=unspecified entries=2 op=nft_register_gen pid=396 subj=system_u:system_r:firewalld_t:s0 comm=firewalld
> >   ...
> >   type=NETFILTER_CFG msg=audit(2020-05-28 17:46:41.878:162) : table=firewalld:1;?:0 family=inet entries=0 op=nft_register_table pid=396 subj=system_u:system_r:firewalld_t:s0 comm=firewalld
> >   ...
> >   type=NETFILTER_CFG msg=audit(2020-05-28 17:46:41.911:163) : table=firewalld:1;filter_FORWARD:85 family=inet entries=8 op=nft_register_chain pid=396 subj=system_u:system_r:firewalld_t:s0 comm=firewalld
> >   ...
> >   type=NETFILTER_CFG msg=audit(2020-05-28 17:46:41.911:163) : table=firewalld:1;filter_FORWARD:85 family=inet entries=101 op=nft_register_rule pid=396 subj=system_u:system_r:firewalld_t:s0 comm=firewalld
> >   ...
> >   type=NETFILTER_CFG msg=audit(2020-05-28 17:46:41.911:163) : table=firewalld:1;__set0:87 family=inet entries=87 op=nft_register_setelem pid=396 subj=system_u:system_r:firewalld_t:s0 comm=firewalld
> >   ...
> >   type=NETFILTER_CFG msg=audit(2020-05-28 17:46:41.911:163) : table=firewalld:1;__set0:87 family=inet entries=0 op=nft_register_set pid=396 subj=system_u:system_r:firewalld_t:s0 comm=firewalld
> >
> > For further information please see issue
> > https://github.com/linux-audit/audit-kernel/issues/124
> >
> > Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
> > ---
> > Changelog:
> > v2:
> > - differentiate between xtables and nftables
> > - add set, setelem, obj, flowtable, gen
> > - use nentries field as appropriate per type
> > - overload the "tables" field with table handle and chain/set/flowtable
> >
> >  include/linux/audit.h         | 52 +++++++++++++++++++++++++
> >  kernel/auditsc.c              | 24 ++++++++++--
> >  net/netfilter/nf_tables_api.c | 89 +++++++++++++++++++++++++++++++++++++++++++
> >  3 files changed, 162 insertions(+), 3 deletions(-)
> >
> > diff --git a/include/linux/audit.h b/include/linux/audit.h
> > index 3fcd9ee49734..d79866a38505 100644
> > --- a/include/linux/audit.h
> > +++ b/include/linux/audit.h
> > @@ -12,6 +12,7 @@
> >  #include <linux/sched.h>
> >  #include <linux/ptrace.h>
> >  #include <uapi/linux/audit.h>
> > +#include <uapi/linux/netfilter/nf_tables.h>
> >
> >  #define AUDIT_INO_UNSET ((unsigned long)-1)
> >  #define AUDIT_DEV_UNSET ((dev_t)-1)
> > @@ -98,6 +99,57 @@ enum audit_nfcfgop {
> >         AUDIT_XT_OP_REGISTER,
> >         AUDIT_XT_OP_REPLACE,
> >         AUDIT_XT_OP_UNREGISTER,
> > +       AUDIT_NFT_OP_TABLE_REGISTER,
> > +       AUDIT_NFT_OP_TABLE_UNREGISTER,
> > +       AUDIT_NFT_OP_CHAIN_REGISTER,
> > +       AUDIT_NFT_OP_CHAIN_UNREGISTER,
> > +       AUDIT_NFT_OP_RULE_REGISTER,
> > +       AUDIT_NFT_OP_RULE_UNREGISTER,
> > +       AUDIT_NFT_OP_SET_REGISTER,
> > +       AUDIT_NFT_OP_SET_UNREGISTER,
> > +       AUDIT_NFT_OP_SETELEM_REGISTER,
> > +       AUDIT_NFT_OP_SETELEM_UNREGISTER,
> > +       AUDIT_NFT_OP_GEN_REGISTER,
> > +       AUDIT_NFT_OP_OBJ_REGISTER,
> > +       AUDIT_NFT_OP_OBJ_UNREGISTER,
> > +       AUDIT_NFT_OP_OBJ_RESET,
> > +       AUDIT_NFT_OP_FLOWTABLE_REGISTER,
> > +       AUDIT_NFT_OP_FLOWTABLE_UNREGISTER,
> > +       AUDIT_NFT_OP_INVALID,
> > +};
> > +
> > +struct audit_nftcfgop_tab {
> > +       enum nf_tables_msg_types        nftop;
> > +       enum audit_nfcfgop              op;
> > +};
> > +
> > +static const struct audit_nftcfgop_tab audit_nftcfgs[] = {
> > +       { NFT_MSG_NEWTABLE,     AUDIT_NFT_OP_TABLE_REGISTER             },
> > +       { NFT_MSG_GETTABLE,     AUDIT_NFT_OP_INVALID                    },
> > +       { NFT_MSG_DELTABLE,     AUDIT_NFT_OP_TABLE_UNREGISTER           },
> > +       { NFT_MSG_NEWCHAIN,     AUDIT_NFT_OP_CHAIN_REGISTER             },
> > +       { NFT_MSG_GETCHAIN,     AUDIT_NFT_OP_INVALID                    },
> > +       { NFT_MSG_DELCHAIN,     AUDIT_NFT_OP_CHAIN_UNREGISTER           },
> > +       { NFT_MSG_NEWRULE,      AUDIT_NFT_OP_RULE_REGISTER              },
> > +       { NFT_MSG_GETRULE,      AUDIT_NFT_OP_INVALID                    },
> > +       { NFT_MSG_DELRULE,      AUDIT_NFT_OP_RULE_UNREGISTER            },
> > +       { NFT_MSG_NEWSET,       AUDIT_NFT_OP_SET_REGISTER               },
> > +       { NFT_MSG_GETSET,       AUDIT_NFT_OP_INVALID                    },
> > +       { NFT_MSG_DELSET,       AUDIT_NFT_OP_SET_UNREGISTER             },
> > +       { NFT_MSG_NEWSETELEM,   AUDIT_NFT_OP_SETELEM_REGISTER           },
> > +       { NFT_MSG_GETSETELEM,   AUDIT_NFT_OP_INVALID                    },
> > +       { NFT_MSG_DELSETELEM,   AUDIT_NFT_OP_SETELEM_UNREGISTER         },
> > +       { NFT_MSG_NEWGEN,       AUDIT_NFT_OP_GEN_REGISTER               },
> > +       { NFT_MSG_GETGEN,       AUDIT_NFT_OP_INVALID                    },
> > +       { NFT_MSG_TRACE,        AUDIT_NFT_OP_INVALID                    },
> > +       { NFT_MSG_NEWOBJ,       AUDIT_NFT_OP_OBJ_REGISTER               },
> > +       { NFT_MSG_GETOBJ,       AUDIT_NFT_OP_INVALID                    },
> > +       { NFT_MSG_DELOBJ,       AUDIT_NFT_OP_OBJ_UNREGISTER             },
> > +       { NFT_MSG_GETOBJ_RESET, AUDIT_NFT_OP_OBJ_RESET                  },
> > +       { NFT_MSG_NEWFLOWTABLE, AUDIT_NFT_OP_FLOWTABLE_REGISTER         },
> > +       { NFT_MSG_GETFLOWTABLE, AUDIT_NFT_OP_INVALID                    },
> > +       { NFT_MSG_DELFLOWTABLE, AUDIT_NFT_OP_FLOWTABLE_UNREGISTER       },
> > +       { NFT_MSG_MAX,          AUDIT_NFT_OP_INVALID                    },
> >  };
> 
> I didn't check every "op" defined above to match with the changes in
> nf_tables_api.c, but is there a reason why we can't simply hardcode
> the AUDIT_NFT_OP_* values in the audit_log_nfcfg() calls in
> nf_tables_api.c?  If we can, let's do that.

Yes, to distinguish between x/ebtables and nftables.  The first three
overlap (as suggested by the first comment in the changelog above).

> If we can't do that, we need to add some build-time protection to
> catch if NFT_MSG_MAX increases without this table being updated.

I would have liked to do that, but it would then have meant making a new
function name, say audit_log_nftcfg vs the original audit_log_nfcfg so
that the overlapping values could be translated appropriately with the
correct prefix.

Well, considering the buildbot error, I had to restructure it so that
the table was moved from include/linux/audit.h to
net/netfilter/nf_tables_api.c where it would be a bit more evident.

At first I thought the bot was complaining about the first field not
being used, but it turned out it was ptrace that was including it and
not using it.

> >  static int audit_match_perm(struct audit_context *ctx, int mask)
> > diff --git a/net/netfilter/nf_tables_api.c b/net/netfilter/nf_tables_api.c
> > index 4471393da6d8..7a386eca6e04 100644
> > --- a/net/netfilter/nf_tables_api.c
> > +++ b/net/netfilter/nf_tables_api.c
> > @@ -12,6 +12,7 @@
> >  #include <linux/netlink.h>
> >  #include <linux/vmalloc.h>
> >  #include <linux/rhashtable.h>
> > +#include <linux/audit.h>
> >  #include <linux/netfilter.h>
> >  #include <linux/netfilter/nfnetlink.h>
> >  #include <linux/netfilter/nf_tables.h>
> > @@ -693,6 +694,14 @@ static void nf_tables_table_notify(const struct nft_ctx *ctx, int event)
> >  {
> >         struct sk_buff *skb;
> >         int err;
> > +       char *buf = kasprintf(GFP_KERNEL, "%s:%llu;?:0",
> > +                             ctx->table->name, ctx->table->handle);
> > +
> > +       audit_log_nfcfg(buf,
> > +                       ctx->family,
> > +                       ctx->table->use,
> > +                       audit_nftcfgs[event].op);
> 
> As an example, the below would work, yes?
> 
> audit_log_nfcfg(...,
>  (event == NFT_MSG_NEWTABLE ?
>   AUDIT_NFT_OP_TABLE_REGISTER :
>   AUDIT_NFT_OP_TABLE_UNREGISTER)

Ok, I see what you are getting at now...  Yes, it could be done this
way, but it seems noisier to me.

> > +       kfree(buf);
> >
> >         if (!ctx->report &&
> >             !nfnetlink_has_listeners(ctx->net, NFNLGRP_NFTABLES))
> 
> paul moore

- RGB

--
Richard Guy Briggs <rgb@redhat.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

--
Linux-audit mailing list
Linux-audit@redhat.com
https://www.redhat.com/mailman/listinfo/linux-audit