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

[Paul Moore]

On Thu, May 28, 2020 at 9:44 PM Richard Guy Briggs <rgb@xxxxxxxxxx> 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@xxxxxxxxxx>
> ---
> 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.

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.

>  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)

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

-- 
paul moore
www.paul-moore.com