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SubjectRe: [PATCH V1] audit: try harder to send to auditd upon netlink failure
On Friday, September 04, 2015 05:14:54 AM Richard Guy Briggs wrote:
> There are several reports of the kernel losing contact with auditd ...

Even if this doesn't completely solve the problem, I like the extra reporting
and robustness of this change. Some comments inline ...

> diff --git a/kernel/audit.c b/kernel/audit.c
> index 1c13e42..4ee114a 100644
> --- a/kernel/audit.c
> +++ b/kernel/audit.c
> @@ -404,19 +404,54 @@ static void audit_printk_skb(struct sk_buff *skb)
> audit_hold_skb(skb);
> }
>
> +static char *audit_strerror(int err)
> +{
> + switch (err) {
> + case -ECONNREFUSED:
> + return "ECONNREFUSED";
> + case -EPERM:
> + return "EPERM";
> + case -ENOMEM:
> + return "ENOMEM";
> + case -EAGAIN:
> + return "EAGAIN";
> + case -ERESTARTSYS:
> + return "ERESTARTSYS";
> + case -EINTR:
> + return "EINTR";
> + default:
> + return "(other)";
> + }
> +}

See comments below.

> static void kauditd_send_skb(struct sk_buff *skb)
> {
> int err;
> + int attempts = 0;
> +#define AUDITD_RETRIES 5
> +
> +restart:
> /* take a reference in case we can't send it and we want to hold it */
> skb_get(skb);

Should the restart label go after the skb_get() call? It seems like if we
ever jump to restart we could end up needlessly bumping the skb's refcnt.

> err = netlink_unicast(audit_sock, skb, audit_nlk_portid, 0);
> if (err < 0) {
> BUG_ON(err != -ECONNREFUSED); /* Shouldn't happen */
> + pr_err("netlink_unicast sending to audit_pid=%d returned error: %d,
%s\n"
> + , audit_pid, err, audit_strerror(err));

This is a style nit, but please put the comma on the preceding line. I know
why you did it, but it bothers me.

I'm also debating if audit_strerror() is worth it. I agree with you that it
is a good idea to indicate the specific error code, I'm just not sure we need
to bother translating that into a proper errno name. Can you think of some
reason why we would need the errno name as opposed to the integer?

> if (audit_pid) {
> - pr_err("*NO* daemon at audit_pid=%d\n", audit_pid);
> - audit_log_lost("auditd disappeared");
> - audit_pid = 0;
> - audit_sock = NULL;
> + if (err == -ECONNREFUSED || err == -EPERM
> + || ++attempts >= AUDITD_RETRIES) {
> + audit_log_lost("audit_pid=%d reset");
> + audit_pid = 0;
> + audit_sock = NULL;
> + } else {
> + pr_warn("re-scheduling(#%d) write to audit_pid=%d\n"
> + , attempts, audit_pid);

Same thing with the comma.

> + set_current_state(TASK_INTERRUPTIBLE);
> + schedule();
> + __set_current_state(TASK_RUNNING);
> + goto restart;

See my comment above about the skb's reference count.

> + }
> }
> /* we might get lucky and get this in the next auditd */
> audit_hold_skb(skb);

--
paul moore
www.paul-moore.com



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