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SubjectRe: Audit vs netlink interaction problem
* Thomas Graf <tgraf@suug.ch> 2008-03-14 19:29
> * Pavel Emelyanov <xemul@openvz.org> 2008-03-14 20:05
> > Hmmm... I'm afraid, that this can break the audit filtering and signal
> > auditing. I haven't yet looked deep into it, but it compares the
> > task->tgid with this audit_pid for different purposes. If audit_pid
> > changes this code will be broken.
>
> OK, then both pids have to be stored. audit_pid remains as-is but is
> no longer used as destination netlink pid. A second pid is stored and
> updated whenever a netlink message is received from userspace.

The following patch represents what I mean. Untested!

Index: net-2.6.26/kernel/audit.c
===================================================================
--- net-2.6.26.orig/kernel/audit.c 2008-03-14 19:31:53.000000000 +0100
+++ net-2.6.26/kernel/audit.c 2008-03-14 19:38:35.000000000 +0100
@@ -82,6 +82,9 @@
* contains the (non-zero) pid. */
int audit_pid;

+/* Actual netlink pid of the userspace process */
+static int audit_nlk_pid;
+
/* If audit_rate_limit is non-zero, limit the rate of sending audit records
* to that number per second. This prevents DoS attacks, but results in
* audit records being dropped. */
@@ -347,12 +350,12 @@
skb = skb_dequeue(&audit_skb_queue);
wake_up(&audit_backlog_wait);
if (skb) {
- if (audit_pid) {
- int err = netlink_unicast(audit_sock, skb, audit_pid, 0);
+ if (audit_nlk_pid) {
+ int err = netlink_unicast(audit_sock, skb, audit_nlk_pid, 0);
if (err < 0) {
BUG_ON(err != -ECONNREFUSED); /* Shoudn't happen */
- printk(KERN_ERR "audit: *NO* daemon at audit_pid=%d\n", audit_pid);
- audit_pid = 0;
+ printk(KERN_ERR "audit: *NO* daemon at audit_nlk_pid=%d\n", audit_nlk_pid);
+ audit_nlk_pid = 0;
}
} else {
if (printk_ratelimit())
@@ -623,6 +626,12 @@
sid, 1);

audit_pid = new_pid;
+
+ /*
+ * Netlink pid is only updated here to avoid overwrites
+ * from potential processes only querying the interface.
+ */
+ audit_nlk_pid = NETLINK_CB(skb).pid;
}
if (status_get->mask & AUDIT_STATUS_RATE_LIMIT)
err = audit_set_rate_limit(status_get->rate_limit,
@@ -1350,7 +1359,7 @@
if (!audit_rate_check()) {
audit_log_lost("rate limit exceeded");
} else {
- if (audit_pid) {
+ if (audit_nlk_pid) {
struct nlmsghdr *nlh = nlmsg_hdr(ab->skb);
nlh->nlmsg_len = ab->skb->len - NLMSG_SPACE(0);
skb_queue_tail(&audit_skb_queue, ab->skb);

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