AUDIT: Send netlink messages from a separate kernel thread

netlink_unicast() will attempt to reallocate and will free messages if
the socket's rcvbuf limit is reached unless we give it an infinite
timeout. So do that, from a kernel thread which is dedicated to spewing
stuff up the netlink socket.

Signed-off-by: David Woodhouse <dwmw2@infradead.org>

diff --git a/kernel/audit.c b/kernel/audit.c
index dae3570b3a3b0660881b00701cb25f3af9a93afa..bbc6f542c8f7852b1da7a69003cd4fe560d82576 100644 (file)
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -46,6 +46,8 @@
 #include <asm/types.h>
 #include <linux/mm.h>
 #include <linux/module.h>
 #include <asm/types.h>
 #include <linux/mm.h>
 #include <linux/module.h>

+#include <linux/err.h>
+#include <linux/kthread.h>

 
 #include <linux/audit.h>
 
 
 #include <linux/audit.h>
 


@@ -77,7 +79,6 @@ static int    audit_rate_limit;
 
 /* Number of outstanding audit_buffers allowed. */
 static int     audit_backlog_limit = 64;
 
 /* Number of outstanding audit_buffers allowed. */
 static int     audit_backlog_limit = 64;

-static atomic_t        audit_backlog       = ATOMIC_INIT(0);

 
 /* The identity of the user shutting down the audit system. */
 uid_t          audit_sig_uid = -1;
 
 /* The identity of the user shutting down the audit system. */
 uid_t          audit_sig_uid = -1;


@@ -95,19 +96,17 @@ static atomic_t    audit_lost = ATOMIC_INIT(0);
 /* The netlink socket. */
 static struct sock *audit_sock;
 
 /* The netlink socket. */
 static struct sock *audit_sock;
 

-/* There are two lists of audit buffers.  The txlist contains audit
- * buffers that cannot be sent immediately to the netlink device because
- * we are in an irq context (these are sent later in a tasklet).
- *
- * The second list is a list of pre-allocated audit buffers (if more
+/* The audit_freelist is a list of pre-allocated audit buffers (if more

  * than AUDIT_MAXFREE are in use, the audit buffer is freed instead of
  * being placed on the freelist). */
  * than AUDIT_MAXFREE are in use, the audit buffer is freed instead of
  * being placed on the freelist). */

-static DEFINE_SPINLOCK(audit_txlist_lock);

 static DEFINE_SPINLOCK(audit_freelist_lock);
 static int        audit_freelist_count = 0;
 static DEFINE_SPINLOCK(audit_freelist_lock);
 static int        audit_freelist_count = 0;

-static LIST_HEAD(audit_txlist);

 static LIST_HEAD(audit_freelist);
 
 static LIST_HEAD(audit_freelist);
 

+static struct sk_buff_head audit_skb_queue;
+static struct task_struct *kauditd_task;
+static DECLARE_WAIT_QUEUE_HEAD(kauditd_wait);
+

 /* There are three lists of rules -- one to search at task creation
  * time, one to search at syscall entry time, and another to search at
  * syscall exit time. */
 /* There are three lists of rules -- one to search at task creation
  * time, one to search at syscall entry time, and another to search at
  * syscall exit time. */


@@ -151,9 +150,6 @@ struct audit_entry {
        struct audit_rule rule;
 };
 
        struct audit_rule rule;
 };
 

-static void audit_log_end_irq(struct audit_buffer *ab);
-static void audit_log_end_fast(struct audit_buffer *ab);
-

 static void audit_panic(const char *message)
 {
        switch (audit_failure)
 static void audit_panic(const char *message)
 {
        switch (audit_failure)


@@ -224,10 +220,8 @@ void audit_log_lost(const char *message)
 
        if (print) {
                printk(KERN_WARNING
 
        if (print) {
                printk(KERN_WARNING

-                      "audit: audit_lost=%d audit_backlog=%d"
-                      " audit_rate_limit=%d audit_backlog_limit=%d\n",
+                      "audit: audit_lost=%d audit_rate_limit=%d audit_backlog_limit=%d\n",

                       atomic_read(&audit_lost),
                       atomic_read(&audit_lost),

-                      atomic_read(&audit_backlog),

                       audit_rate_limit,
                       audit_backlog_limit);
                audit_panic(message);
                       audit_rate_limit,
                       audit_backlog_limit);
                audit_panic(message);


@@ -281,6 +275,38 @@ static int audit_set_failure(int state, uid_t loginuid)
        return old;
 }
 
        return old;
 }
 

+int kauditd_thread(void *dummy)
+{
+       struct sk_buff *skb;
+
+       while (1) {
+               skb = skb_dequeue(&audit_skb_queue);
+               if (skb) {
+                       if (audit_pid) {
+                               int err = netlink_unicast(audit_sock, skb, audit_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;
+                               }
+                       } else {
+                               printk(KERN_ERR "%s\n", skb->data + NLMSG_SPACE(0));
+                               kfree_skb(skb);
+                       }
+               } else {
+                       DECLARE_WAITQUEUE(wait, current);
+                       set_current_state(TASK_INTERRUPTIBLE);
+                       add_wait_queue(&kauditd_wait, &wait);
+
+                       if (!skb_queue_len(&audit_skb_queue))
+                               schedule();
+
+                       __set_current_state(TASK_RUNNING);
+                       remove_wait_queue(&kauditd_wait, &wait);
+               }
+       }
+}
+

 void audit_send_reply(int pid, int seq, int type, int done, int multi,
                      void *payload, int size)
 {
 void audit_send_reply(int pid, int seq, int type, int done, int multi,
                      void *payload, int size)
 {


@@ -293,13 +319,16 @@ void audit_send_reply(int pid, int seq, int type, int done, int multi,
 
        skb = alloc_skb(len, GFP_KERNEL);
        if (!skb)
 
        skb = alloc_skb(len, GFP_KERNEL);
        if (!skb)

-               goto nlmsg_failure;
+               return;

 
 

-       nlh              = NLMSG_PUT(skb, pid, seq, t, len - sizeof(*nlh));
+       nlh              = NLMSG_PUT(skb, pid, seq, t, size);

        nlh->nlmsg_flags = flags;
        data             = NLMSG_DATA(nlh);
        memcpy(data, payload, size);
        nlh->nlmsg_flags = flags;
        data             = NLMSG_DATA(nlh);
        memcpy(data, payload, size);

-       netlink_unicast(audit_sock, skb, pid, MSG_DONTWAIT);
+
+       /* Ignore failure. It'll only happen if the sender goes away,
+          because our timeout is set to infinite. */
+       netlink_unicast(audit_sock, skb, pid, 0);

        return;
 
 nlmsg_failure:                 /* Used by NLMSG_PUT */
        return;
 
 nlmsg_failure:                 /* Used by NLMSG_PUT */


@@ -351,6 +380,15 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
        if (err)
                return err;
 
        if (err)
                return err;
 

+       /* As soon as there's any sign of userspace auditd, start kauditd to talk to it */
+       if (!kauditd_task)
+               kauditd_task = kthread_run(kauditd_thread, NULL, "kauditd");
+       if (IS_ERR(kauditd_task)) {
+               err = PTR_ERR(kauditd_task);
+               kauditd_task = NULL;
+               return err;
+       }
+

        pid  = NETLINK_CREDS(skb)->pid;
        uid  = NETLINK_CREDS(skb)->uid;
        loginuid = NETLINK_CB(skb).loginuid;
        pid  = NETLINK_CREDS(skb)->pid;
        uid  = NETLINK_CREDS(skb)->uid;
        loginuid = NETLINK_CB(skb).loginuid;


@@ -365,7 +403,7 @@ static int audit_receive_msg(struct sk_buff *skb, struct nlmsghdr *nlh)
                status_set.rate_limit    = audit_rate_limit;
                status_set.backlog_limit = audit_backlog_limit;
                status_set.lost          = atomic_read(&audit_lost);
                status_set.rate_limit    = audit_rate_limit;
                status_set.backlog_limit = audit_backlog_limit;
                status_set.lost          = atomic_read(&audit_lost);

-               status_set.backlog       = atomic_read(&audit_backlog);
+               status_set.backlog       = skb_queue_len(&audit_skb_queue);

                audit_send_reply(NETLINK_CB(skb).pid, seq, AUDIT_GET, 0, 0,
                                 &status_set, sizeof(status_set));
                break;
                audit_send_reply(NETLINK_CB(skb).pid, seq, AUDIT_GET, 0, 0,
                                 &status_set, sizeof(status_set));
                break;


@@ -471,44 +509,6 @@ static void audit_receive(struct sock *sk, int length)
        up(&audit_netlink_sem);
 }
 
        up(&audit_netlink_sem);
 }
 

-/* Grab skbuff from the audit_buffer and send to user space. */
-static inline int audit_log_drain(struct audit_buffer *ab)
-{
-       struct sk_buff *skb = ab->skb;
-
-       if (skb) {
-               int retval = 0;
-
-               if (audit_pid) {
-                       struct nlmsghdr *nlh = (struct nlmsghdr *)skb->data;
-                       nlh->nlmsg_len = skb->len - NLMSG_SPACE(0);
-                       skb_get(skb); /* because netlink_* frees */
-                       retval = netlink_unicast(audit_sock, skb, audit_pid,
-                                                MSG_DONTWAIT);
-               }
-               if (retval == -EAGAIN &&
-                   (atomic_read(&audit_backlog)) < audit_backlog_limit) {
-                       audit_log_end_irq(ab);
-                       return 1;
-               }
-               if (retval < 0) {
-                       if (retval == -ECONNREFUSED) {
-                               printk(KERN_ERR
-                                      "audit: *NO* daemon at audit_pid=%d\n",
-                                      audit_pid);
-                               audit_pid = 0;
-                       } else
-                               audit_log_lost("netlink socket too busy");
-               }
-               if (!audit_pid) { /* No daemon */
-                       int offset = NLMSG_SPACE(0);
-                       int len    = skb->len - offset;
-                       skb->data[offset + len] = '\0';
-                       printk(KERN_ERR "%s\n", skb->data + offset);
-               }
-       }
-       return 0;
-}

 
 /* Initialize audit support at boot time. */
 static int __init audit_init(void)
 
 /* Initialize audit support at boot time. */
 static int __init audit_init(void)


@@ -519,6 +519,8 @@ static int __init audit_init(void)
        if (!audit_sock)
                audit_panic("cannot initialize netlink socket");
 
        if (!audit_sock)
                audit_panic("cannot initialize netlink socket");
 

+       audit_sock->sk_sndtimeo = MAX_SCHEDULE_TIMEOUT;
+       skb_queue_head_init(&audit_skb_queue);

        audit_initialized = 1;
        audit_enabled = audit_default;
        audit_log(NULL, AUDIT_KERNEL, "initialized");
        audit_initialized = 1;
        audit_enabled = audit_default;
        audit_log(NULL, AUDIT_KERNEL, "initialized");


@@ -549,7 +551,7 @@ static void audit_buffer_free(struct audit_buffer *ab)
 
        if (ab->skb)
                kfree_skb(ab->skb);
 
        if (ab->skb)
                kfree_skb(ab->skb);

-       atomic_dec(&audit_backlog);
+

        spin_lock_irqsave(&audit_freelist_lock, flags);
        if (++audit_freelist_count > AUDIT_MAXFREE)
                kfree(ab);
        spin_lock_irqsave(&audit_freelist_lock, flags);
        if (++audit_freelist_count > AUDIT_MAXFREE)
                kfree(ab);


@@ -579,13 +581,12 @@ static struct audit_buffer * audit_buffer_alloc(struct audit_context *ctx,
                if (!ab)
                        goto err;
        }
                if (!ab)
                        goto err;
        }

-       atomic_inc(&audit_backlog);

 
        ab->skb = alloc_skb(AUDIT_BUFSIZ, gfp_mask);
        if (!ab->skb)
                goto err;
 
 
        ab->skb = alloc_skb(AUDIT_BUFSIZ, gfp_mask);
        if (!ab->skb)
                goto err;
 

-       ab->ctx   = ctx;
+       ab->ctx = ctx;

        nlh = (struct nlmsghdr *)skb_put(ab->skb, NLMSG_SPACE(0));
        nlh->nlmsg_type = type;
        nlh->nlmsg_flags = 0;
        nlh = (struct nlmsghdr *)skb_put(ab->skb, NLMSG_SPACE(0));
        nlh->nlmsg_type = type;
        nlh->nlmsg_flags = 0;


@@ -612,18 +613,6 @@ struct audit_buffer *audit_log_start(struct audit_context *ctx, int type)
        if (!audit_initialized)
                return NULL;
 
        if (!audit_initialized)
                return NULL;
 

-       if (audit_backlog_limit
-           && atomic_read(&audit_backlog) > audit_backlog_limit) {
-               if (audit_rate_check())
-                       printk(KERN_WARNING
-                              "audit: audit_backlog=%d > "
-                              "audit_backlog_limit=%d\n",
-                              atomic_read(&audit_backlog),
-                              audit_backlog_limit);
-               audit_log_lost("backlog limit exceeded");
-               return NULL;
-       }
-

        ab = audit_buffer_alloc(ctx, GFP_ATOMIC, type);
        if (!ab) {
                audit_log_lost("out of memory in audit_log_start");
        ab = audit_buffer_alloc(ctx, GFP_ATOMIC, type);
        if (!ab) {
                audit_log_lost("out of memory in audit_log_start");


@@ -784,70 +773,30 @@ void audit_log_d_path(struct audit_buffer *ab, const char *prefix,
        kfree(path);
 }
 
        kfree(path);
 }
 

-/* Remove queued messages from the audit_txlist and send them to user space. */
-static void audit_tasklet_handler(unsigned long arg)
-{
-       LIST_HEAD(list);
-       struct audit_buffer *ab;
-       unsigned long       flags;
-
-       spin_lock_irqsave(&audit_txlist_lock, flags);
-       list_splice_init(&audit_txlist, &list);
-       spin_unlock_irqrestore(&audit_txlist_lock, flags);
-
-       while (!list_empty(&list)) {
-               ab = list_entry(list.next, struct audit_buffer, list);
-               list_del(&ab->list);
-               audit_log_end_fast(ab);
-       }
-}
-
-static DECLARE_TASKLET(audit_tasklet, audit_tasklet_handler, 0);
-

 /* The netlink_* functions cannot be called inside an irq context, so
  * the audit buffer is places on a queue and a tasklet is scheduled to
  * remove them from the queue outside the irq context.  May be called in
  * any context. */
 /* The netlink_* functions cannot be called inside an irq context, so
  * the audit buffer is places on a queue and a tasklet is scheduled to
  * remove them from the queue outside the irq context.  May be called in
  * any context. */

-static void audit_log_end_irq(struct audit_buffer *ab)
-{
-       unsigned long flags;
-
-       if (!ab)
-               return;
-       spin_lock_irqsave(&audit_txlist_lock, flags);
-       list_add_tail(&ab->list, &audit_txlist);
-       spin_unlock_irqrestore(&audit_txlist_lock, flags);
-
-       tasklet_schedule(&audit_tasklet);
-}
-
-/* Send the message in the audit buffer directly to user space.  May not
- * be called in an irq context. */
-static void audit_log_end_fast(struct audit_buffer *ab)
+void audit_log_end(struct audit_buffer *ab)

 {
 {

-       BUG_ON(in_irq());

        if (!ab)
                return;
        if (!audit_rate_check()) {
                audit_log_lost("rate limit exceeded");
        } else {
        if (!ab)
                return;
        if (!audit_rate_check()) {
                audit_log_lost("rate limit exceeded");
        } else {

-               if (audit_log_drain(ab))
-                       return;
+               if (audit_pid) {
+                       struct nlmsghdr *nlh = (struct nlmsghdr *)ab->skb->data;
+                       nlh->nlmsg_len = ab->skb->len - NLMSG_SPACE(0);
+                       skb_queue_tail(&audit_skb_queue, ab->skb);
+                       ab->skb = NULL;
+                       wake_up_interruptible(&kauditd_wait);
+               } else {
+                       printk("%s\n", ab->skb->data + NLMSG_SPACE(0));
+               }

        }
        audit_buffer_free(ab);
 }
 
        }
        audit_buffer_free(ab);
 }
 

-/* Send or queue the message in the audit buffer, depending on the
- * current context.  (A convenience function that may be called in any
- * context.) */
-void audit_log_end(struct audit_buffer *ab)
-{
-       if (in_irq())
-               audit_log_end_irq(ab);
-       else
-               audit_log_end_fast(ab);
-}
-

 /* Log an audit record.  This is a convenience function that calls
  * audit_log_start, audit_log_vformat, and audit_log_end.  It may be
  * called in any context. */
 /* Log an audit record.  This is a convenience function that calls
  * audit_log_start, audit_log_vformat, and audit_log_end.  It may be
  * called in any context. */