Re: [PATCH V1] audit: add warning that an old auditd may be starved out by a new auditd

[Eric Paris <eparis@redhat.com>]

This is already going to be in the audit log, right? We're going to
send a CONFIG_CHANGE record with old_pid == the existing auditd. I bet
it gets delivered to the old auditd.

But why is this a printk(KERN_WARN) ?

On Mon, 2015-09-07 at 12:48 -0400, Richard Guy Briggs wrote:
> Nothing prevents a new auditd starting up and replacing a valid
> audit_pid when an old auditd is still running, effectively starving
> out
> the old auditd since audit_pid no longer points to the old valid
> auditd.
> 
> There isn't an easy way to detect if an old auditd is still running
> on
> the existing audit_pid other than attempting to send a message to see
> if
> it fails.  If no message to auditd has been attempted since auditd
> died
> unnaturally or got killed, audit_pid will still indicate it is alive.
> 
> Signed-off-by: Richard Guy Briggs <rgb@redhat.com>
> ---
> Note: Would it be too bold to actually block the registration of a
> new
> auditd if the netlink_getsockbyportid() call succeeded?  Would other
> checks be appropriate?
> 
>  kernel/audit.c |    5 +++++
>  1 files changed, 5 insertions(+), 0 deletions(-)
> 
> diff --git a/kernel/audit.c b/kernel/audit.c
> index 18cdfe2..1fa1e0d 100644
> --- a/kernel/audit.c
> +++ b/kernel/audit.c
> @@ -872,6 +872,11 @@ static int audit_receive_msg(struct sk_buff
> *skb, struct nlmsghdr *nlh)
>  		if (s.mask & AUDIT_STATUS_PID) {
>  			int new_pid = s.pid;
>  
> +			if (audit_pid && new_pid &&
> +			   
>  !IS_ERR(netlink_getsockbyportid(audit_sock, audit_nlk_portid)))
> +				pr_warn("auditd replaced by new
> auditd before normal shutdown: "
> +					"(old)audit_pid=%d
> (by)pid=%d new_pid=%d",
> +					audit_pid, pid, new_pid);
>  			if ((!new_pid) && (task_tgid_vnr(current) !=
> audit_pid))
>  				return -EACCES;
>  			if (audit_enabled != AUDIT_OFF)