Audit: netlink socket can be auto-bound to pid other than current->pid

PATCH In review Pavel Emelyanov 2 participants 5 messages Mar 18, 2008 – Mar 19, 2008 Audit

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Pavel Emelyanov

author

2008-03-18 09:24 UTC #0 lore raw

PATCH 1/1 Audit: netlink socket can be auto-bound to pid other than current->pid

This patch is based on the one from Thomas.

The kauditd_thread() calls the netlink_unicast() and passes the audit_pid to it. The audit_pid, in turn, is received from the user space and the tool (I've checked the audit v1.6.9) uses getpid() to pass one in the kernel. Besides, this tool doesn't bind the netlink socket to this id, but simply creates it allowing the kernel to auto-bind one.

That's the preamble.

The problem is that netlink_autobind() _does_not_ guarantees that the socket will be auto-bound to the current pid. Instead it uses the current pid as a hint to start looking for a free id. So, in case of conflict, the audit messages can be sent to a wrong socket. This can happen (it's unlikely, but can be) in case some task opens more than one netlink sockets and then the audit one starts - in this case the audit's pid can be busy and its socket will be bound to another id.

The proposal is to introduce an audit_nlk_pid in audit subsys, that will point to the netlink socket to send packets to. It will most often be equal to audit_pid. The socket id can be got from the skb's netlink CB right in the audit_receive_msg.

Later, if the audit tools will bind the socket themselves, the kernel will have to provide a way to setup the audit_nlk_pid as well.

A good side effect of this patch is that audit_pid can later be converted to struct pid, as it is not longer safe to use pid_t-s in the presence of pid namespaces. But audit code still uses the tgid from task_struct in the audit_signal_info and in the audit_filter_syscall.

Signed-off-by Thomas Graf <[email protected]>

Signed-off-by Pavel Emelyanov <[email protected]>

---

kernel/audit.c +9 -6

index 10c4930..40b3a34 100644
@@ -78,8 +78,10 @@ static int	audit_default;
 /* If auditing cannot proceed, audit_failure selects what happens. */
 static int	audit_failure = AUDIT_FAIL_PRINTK;
 
-/* If audit records are to be written to the netlink socket, audit_pid
+/* If audit records are to be written to the netlink socket, audit_nlk_pid
  * contains the (non-zero) pid. */
+static int	audit_nlk_pid;
+
 int		audit_pid;
 
 /* If audit_rate_limit is non-zero, limit the rate of sending audit records

@@ -349,13 +351,13 @@ static int kauditd_thread(void *dummy)
 		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);
+					printk(KERN_ERR "audit: *NO* daemon at audit_nlk_pid=%d\n", audit_nlk_pid);
 					audit_log_lost("auditd dissapeared\n");
-					audit_pid = 0;
+					audit_nlk_pid = 0;
 				}
 			} else {
 				if (printk_ratelimit())

@@ -626,6 +628,7 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
 							sid, 1);
 
 			audit_pid = new_pid;
+			audit_nlk_pid = NETLINK_CB(skb).pid;
 		}
 		if (status_get->mask & AUDIT_STATUS_RATE_LIMIT)
 			err = audit_set_rate_limit(status_get->rate_limit,

@@ -1354,7 +1357,7 @@ void audit_log_end(struct audit_buffer *ab)
 		audit_log_lost("rate limit exceeded");
 	} else {
 		struct nlmsghdr *nlh = nlmsg_hdr(ab->skb);
-		if (audit_pid) {
+		if (audit_nlk_pid) {
 			nlh->nlmsg_len = ab->skb->len - NLMSG_SPACE(0);
 			skb_queue_tail(&audit_skb_queue, ab->skb);
 			ab->skb = NULL;

Eric Paris

2008-03-18 23:30 UTC #1 lore raw

On 3/18/08, Pavel Emelyanov <[email protected]> wrote:

Can we please just leave audit_pid as the one flag to tell us if auditd is supposedly up there in userspace? Use audit_nlk_pid to send messages to the right place, but leave everything else to do with audit_pid alone.

Quoted 10 lines

diff --git a/kernel/audit.c b/kernel/audit.c
index 10c4930..40b3a34 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -78,8 +78,10 @@ static int audit_default;
/* If auditing cannot proceed, audit_failure selects what happens. */
static int audit_failure = AUDIT_FAIL_PRINTK;
-/* If audit records are to be written to the netlink socket, audit_pid +/* If audit records are to be written to the netlink socket, audit_nlk_pid

/* If audit records are to be written to the netlink socket, audit_pid contain the pid of the auditd process and audit_nlk_pid will contain the pid to use to send netlink messages to that process. */

Quoted 5 lines

* contains the (non-zero) pid. */
+static int audit_nlk_pid;
+
int audit_pid;

Quoted 8 lines

/* If audit_rate_limit is non-zero, limit the rate of sending audit records
@@ -349,13 +351,13 @@ static int kauditd_thread(void *dummy)
                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) {

unneeded change

Quoted 1 line

+ int err = netlink_unicast(audit_sock, skb, audit_nlk_pid, 0);

good.

Quoted 4 lines

                                if (err < 0) {
                                        BUG_ON(err != -ECONNREFUSED); /* Shoudn't happen */
- printk(KERN_ERR "audit: *NO* daemon at audit_pid=%d\n", audit_pid);
+ printk(KERN_ERR "audit: *NO* daemon at audit_nlk_pid=%d\n", audit_nlk_pid);

userspace is never going to care about audit_nlk_pid, its meaningless at that level. This message should continue to use audit_pid.

Quoted 2 lines

                                        audit_log_lost("auditd dissapeared\n");

- audit_pid = 0;

We still need to 0 audit_pid otherwise all of the tests which use it are bogus (aka things like audit_panic and audit_filter_syscall you mentioned)

Quoted 16 lines

 +                                       audit_nlk_pid = 0;
                                }
                        } else {
                                if (printk_ratelimit())
 @@ -626,6 +628,7 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
                                                        sid, 1);

                        audit_pid = new_pid;
 +                       audit_nlk_pid = NETLINK_CB(skb).pid;
                }
                if (status_get->mask & AUDIT_STATUS_RATE_LIMIT)
                        err = audit_set_rate_limit(status_get->rate_limit,
 @@ -1354,7 +1357,7 @@ void audit_log_end(struct audit_buffer *ab)
                audit_log_lost("rate limit exceeded");
        } else {
                struct nlmsghdr *nlh = nlmsg_hdr(ab->skb);

Quoted 2 lines

- if (audit_pid) {
+ if (audit_nlk_pid) {

don't need this if we zero audit_pid.

Quoted 4 lines

                        nlh->nlmsg_len = ab->skb->len - NLMSG_SPACE(0);
                        skb_queue_tail(&audit_skb_queue, ab->skb);
                        ab->skb = NULL;

Eric Paris

2008-03-18 23:35 UTC #2 lore raw

Quoted 10 lines · Eric Paris

Quoted 8 lines · Pavel Emelyanov

@@ -626,6 +628,7 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)

                                                        sid, 1);

                        audit_pid = new_pid;
 +                       audit_nlk_pid = NETLINK_CB(skb).pid;
                }
                if (status_get->mask & AUDIT_STATUS_RATE_LIMIT)
                        err = audit_set_rate_limit(status_get->rate_limit,

Shouldn't the above be:

if (audit_pid)

    audit_nlk_pid = NETLINK_CB(skb).pid;

else
audit_nlk_pid = 0;

otherwise I don't see how you can cleanly stop the userspace auditd.....

Pavel Emelyanov

author

2008-03-19 09:11 UTC #3 lore raw

In reply to Eric Paris

Quoted 6 lines · Eric Paris

On 3/18/08, Pavel Emelyanov <[email protected]> wrote:
Can we please just leave audit_pid as the one flag to tell us if auditd is supposedly up there in userspace? Use audit_nlk_pid to send messages to the right place, but leave everything else to do with audit_pid alone.

OK, point taken ;) Is that patch looks OK? If yes, I'll comment it properly and re-send to Andrew.

The audit_nlk_pid reset to 0 is not required, since all the decisions are taken based on audit_pid value only.

Signed-off-by Pavel Emelyanov <[email protected]>

kernel/audit.c +8 -3

index ccc7d0e..12a0278 100644
@@ -77,9 +77,13 @@ static int	audit_default;
 /* If auditing cannot proceed, audit_failure selects what happens. */
 static int	audit_failure = AUDIT_FAIL_PRINTK;
 
-/* If audit records are to be written to the netlink socket, audit_pid
- * contains the (non-zero) pid. */
+/*
+ * If audit records are to be written to the netlink socket, audit_pid
+ * contains the pid of the auditd process and audit_nlk_pid contains
+ * the pid to use to send netlink messages to that process.
+ */
 int		audit_pid;
+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

@@ -349,7 +353,7 @@ static int kauditd_thread(void *dummy)
 		wake_up(&audit_backlog_wait);
 		if (skb) {
 			if (audit_pid) {
-				int err = netlink_unicast(audit_sock, skb, audit_pid, 0);
+				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);

@@ -626,6 +630,7 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
 							sid, 1);
 
 			audit_pid = new_pid;
+			audit_nlk_pid = NETLINK_CB(skb).pid;
 		}
 		if (status_get->mask & AUDIT_STATUS_RATE_LIMIT)
 			err = audit_set_rate_limit(status_get->rate_limit,

Eric Paris

2008-03-19 12:05 UTC #4 lore raw

Quoted 9 lines · Pavel Emelyanov

Quoted 6 lines · Eric Paris
On 3/18/08, Pavel Emelyanov <[email protected]> wrote:
Can we please just leave audit_pid as the one flag to tell us if auditd is supposedly up there in userspace? Use audit_nlk_pid to send messages to the right place, but leave everything else to do with audit_pid alone.

Quoted 5 lines

OK, point taken ;) Is that patch looks OK? If yes, I'll comment
it properly and re-send to Andrew.
The audit_nlk_pid reset to 0 is not required, since all the decisions are taken based on audit_pid value only.

I looks good to me. Feel free to add Acked-by: Eric Paris <[email protected]> on your submission.

-Eric

Quoted 55 lines

Signed-off-by Pavel Emelyanov <[email protected]>

diff --git a/kernel/audit.c b/kernel/audit.c

index ccc7d0e..12a0278 100644

--- a/kernel/audit.c
+++ b/kernel/audit.c

kernel/audit.c +2 -1

@@ -77,9 +77,13 @@ static int   audit_default;
 
 /* If auditing cannot proceed, audit_failure selects what happens. */
  static int     audit_failure = AUDIT_FAIL_PRINTK;
 
 -/* If audit records are to be written to the netlink socket, audit_pid
 
- * contains the (non-zero) pid. */
 +/*
 + * If audit records are to be written to the netlink socket, audit_pid
 + * contains the pid of the auditd process and audit_nlk_pid contains
 + * the pid to use to send netlink messages to that process.
 + */
  int            audit_pid;
 
+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
 @@ -349,7 +353,7 @@ static int kauditd_thread(void *dummy)
 
                wake_up(&audit_backlog_wait);
                if (skb) {
                        if (audit_pid) {
 -                               int err = netlink_unicast(audit_sock, skb, audit_pid, 0);
 
+                               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);

@@ -626,6 +630,7 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
 
                                                        sid, 1);
 
                        audit_pid = new_pid;
 +                       audit_nlk_pid = NETLINK_CB(skb).pid;
                }
                if (status_get->mask & AUDIT_STATUS_RATE_LIMIT)
                        err = audit_set_rate_limit(status_get->rate_limit,