Messages in this thread | | | Date | Fri, 25 Sep 2015 07:10:19 -0400 | From | Richard Guy Briggs <> | Subject | Re: [PATCH 1/2] audit: stop an old auditd being starved out by a new auditd |
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On 15/09/24, Paul Moore wrote: > On Friday, September 18, 2015 03:59:58 AM 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. > > > > If no message to auditd has been attempted since auditd died unnaturally > > or got killed, audit_pid will still indicate it is alive. 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. > > An -ECONNREFUSED almost certainly means it disappeared and can be > > replaced. Other errors are not so straightforward and may indicate > > transient problems that will resolve themselves and the old auditd will > > recover. Yet others will likely need manual intervention for which a > > new auditd will not solve the problem. > > > > Send a new message type (AUDIT_PING) to the old auditd containing a u32 > > with the PID of the new auditd. If the audit ping succeeds (or doesn't > > fail with certainty), fail to register the new auditd and return an > > error (-EEXIST). > > > > This is expected to make the patch preventing an old auditd orphaning a > > new auditd redundant. > > > > Signed-off-by: Richard Guy Briggs <rgb@redhat.com> > > --- > > include/uapi/linux/audit.h | 1 + > > kernel/audit.c | 19 +++++++++++++++++-- > > 2 files changed, 18 insertions(+), 2 deletions(-) > > XXX
???
> > diff --git a/kernel/audit.c b/kernel/audit.c > > index 18cdfe2..3399ab2 100644 > > --- a/kernel/audit.c > > +++ b/kernel/audit.c > > @@ -810,6 +810,15 @@ static int audit_set_feature(struct sk_buff *skb) > > return 0; > > } > > > > +static int audit_ping(pid_t pid, u32 seq, u32 portid) > > +{ > > + struct sk_buff *skb = audit_make_reply(portid, seq, AUDIT_PING, 0, 0, > > + &pid, sizeof(pid)); > > This is almost surely going to end up using the wrong netlink sequence number > and portid since you are passing the new requestor's information below. I > didn't chase down the netlink_unicast() guts to see if it replaces the portid, > it might (it probably does), but that still leaves the sequence number.
It is intended to use the new pid and new netlink sequence number to the old audit_sock and old portid. There is no other sequence number available and it is this new sequence number and pid that needs reporting to the old auditd.
> Also, this is more of a attempted hijack message and not a simple ping, right?
Ok, so maybe AUDIT_PING is not the appropriate name for it. I don't have a problem changing it, but I think the pid of the hijacker would be useful information to the ping-ee unless the ping message was only ever issues in a contextless kernel-initiated message.
> If we want to create a simple ping message, leave the pid out of it; if we > want to indicate to an existing auditd that another process is attempting to > hijack the audit connection then we should probably create a proper audit > record with a type other than AUDIT_PING. I tend to think there is more value > in the hijack message than the ping message, but I can be convinced either > way.
Is there any compelling reason to create a pure ping message that gets sent out periodically to test if auditd is still alive (audit_pid, audit_sock and audit_nlk_portid are valid)? Is there any reason to reserve that AUDIT_PING macro at this time should it be determined that it is necessary in the future?
> > + if (!skb) > > + return -ENOMEM; > > + return netlink_unicast(audit_sock, skb, audit_nlk_portid, 0); > > +} > > ... > > > @@ -871,13 +880,19 @@ static int audit_receive_msg(struct sk_buff *skb, > > if (s.mask & AUDIT_STATUS_PID) { > > int new_pid = s.pid; > > + pid_t requesting_pid = task_tgid_vnr(current); > > + u32 portid = NETLINK_CB(skb).portid; > > > > - if ((!new_pid) && (task_tgid_vnr(current) != audit_pid)) > > + if ((!new_pid) && (requesting_pid != audit_pid)) > > return -EACCES; > > + if (audit_pid && new_pid && > > + audit_ping(requesting_pid, nlmsg_hdr(skb)->..., portid) != > > + -ECONNREFUSED) > > + return -EEXIST; > > See my comments above about audit_ping(). > > > if (audit_enabled != AUDIT_OFF) > > audit_log_config_change("audit_pid", new_pid, audit_pid, 1); > > audit_pid = new_pid; > > - audit_nlk_portid = NETLINK_CB(skb).portid; > > + audit_nlk_portid = portid; > > audit_sock = skb->sk; > > } > > if (s.mask & AUDIT_STATUS_RATE_LIMIT) { > > paul moore
- RGB
-- Richard Guy Briggs <rbriggs@redhat.com> Senior Software Engineer, Kernel Security, AMER ENG Base Operating Systems, Red Hat Remote, Ottawa, Canada Voice: +1.647.777.2635, Internal: (81) 32635, Alt: +1.613.693.0684x3545
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