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

From: Richard Guy Briggs
Date: Mon Sep 07 2015 - 12:49:39 EST

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@xxxxxxxxxx>
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)

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/