[PATCH 1/1] audit: log binding and unbinding to netlink multicast

[Richard Guy Briggs]

On 2017-10-13 19:58, Steve Grubb wrote:
> Log information about programs connecting and disconnecting to the audit
> netlink multicast socket. This is needed so that during investigations a
> security officer can tell who or what had access to the audit trail. This
> helps to meet the FAU_SAR.2 requirement for Common Criteria. Sample
> event:
> 
> type=UNKNOWN[1332] msg=audit(1507924331.540:3): pid=1 uid=0
> auid=4294967295 tty=(none) ses=4294967295 subj=kernel comm="systemd"
> exe="/usr/lib/systemd/systemd" nlnk-grp=1 op=connect res=1
> 
> Signed-off-by: sgrubb <sgrubb at redhat.com>

Reviewed-by: Richard Guy Briggs <rgb at redhat.com>

> ---
>  include/uapi/linux/audit.h |  1 +
>  kernel/audit.c             | 48 ++++++++++++++++++++++++++++++++++++++++++----
>  2 files changed, 45 insertions(+), 4 deletions(-)
> 
> diff --git a/include/uapi/linux/audit.h b/include/uapi/linux/audit.h
> index 0714a66f0e0c..892e63d9f2c1 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_EVENT_LISTENER	1332	/* Task joined multicast read socket */

I assume this is waiting on another patch to be reviewed and merged...
IIRC the maintainer prefers to deal with that merge conflict rather than
accidentally leave a gap if the dependent patch doesn't get merged.

>  #define AUDIT_AVC		1400	/* SE Linux avc denial or grant */
>  #define AUDIT_SELINUX_ERR	1401	/* Internal SE Linux Errors */
> diff --git a/kernel/audit.c b/kernel/audit.c
> index 1baabc9539b4..3d2461be83a8 100644
> --- a/kernel/audit.c
> +++ b/kernel/audit.c
> @@ -1476,22 +1476,61 @@ static void audit_receive(struct sk_buff  *skb)
>  	mutex_unlock(&audit_cmd_mutex);
>  }
>  
> +/* Log information about who is connecting to the audit multicast socket */
> +static void audit_log_multicast_bind(int group, const char *op, int err)
> +{
> +	const struct cred *cred;
> +	struct tty_struct *tty;
> +	char comm[sizeof(current->comm)];
> +	struct audit_buffer *ab;
> +
> +	ab = audit_log_start(NULL, GFP_KERNEL, AUDIT_EVENT_LISTENER);
> +	if (!ab)
> +		return;
> +
> +	cred = current_cred();
> +	tty = audit_get_tty(current);
> +
> +	audit_log_format(ab, "pid=%u uid=%u auid=%u tty=%s ses=%u",
> +			task_pid_nr(current),
> +			from_kuid(&init_user_ns, cred->uid),
> +			from_kuid(&init_user_ns, audit_get_loginuid(current)),
> +			tty ? tty_name(tty) : "(none)",
> +			audit_get_sessionid(current));
> +	audit_put_tty(tty);
> +	audit_log_task_context(ab); /* subj= */
> +	audit_log_format(ab, " comm=");
> +	audit_log_untrustedstring(ab, get_task_comm(comm, current));
> +	audit_log_d_path_exe(ab, current->mm); /* exe= */
> +	audit_log_format(ab, " nlnk-grp=%d op=%s res=%d", group, op, !err);
> +	audit_log_end(ab);
> +}
> +
>  /* Run custom bind function on netlink socket group connect or bind requests. */
> -static int audit_bind(struct net *net, int group)
> +static int audit_multicast_bind(struct net *net, int group)
>  {
> +	int err = 0;
> +
>  	if (!capable(CAP_AUDIT_READ))
> -		return -EPERM;
> +		err = -EPERM;
> +	audit_log_multicast_bind(group, "connect", err);
>  
> -	return 0;
> +	return err;
> +}
> +
> +static void audit_multicast_unbind(struct net *net, int group)
> +{
> +	audit_log_multicast_bind(group, "disconnect", 0);
>  }
>  
>  static int __net_init audit_net_init(struct net *net)
>  {
>  	struct netlink_kernel_cfg cfg = {
>  		.input	= audit_receive,
> -		.bind	= audit_bind,
> +		.bind	= audit_multicast_bind,
>  		.flags	= NL_CFG_F_NONROOT_RECV,
>  		.groups	= AUDIT_NLGRP_MAX,
> +		.unbind = audit_multicast_unbind,
>  	};
>  
>  	struct audit_net *aunet = net_generic(net, audit_net_id);
> -- 
> 2.13.6
> 
> 
> --
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- RGB

--
Richard Guy Briggs <rgb at 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