+static void audit_buffer_free(struct audit_buffer *ab)
+{
+ unsigned long flags;
+
+ if (!ab)
+ return;
+
+ if (ab->skb)
+ kfree_skb(ab->skb);
+
+ spin_lock_irqsave(&audit_freelist_lock, flags);
+ if (++audit_freelist_count > AUDIT_MAXFREE)
+ kfree(ab);
+ else
+ list_add(&ab->list, &audit_freelist);
+ spin_unlock_irqrestore(&audit_freelist_lock, flags);
+}
+
+static struct audit_buffer * audit_buffer_alloc(struct audit_context *ctx,
+ int gfp_mask, int type)
+{
+ unsigned long flags;
+ struct audit_buffer *ab = NULL;
+ struct nlmsghdr *nlh;
+
+ spin_lock_irqsave(&audit_freelist_lock, flags);
+ if (!list_empty(&audit_freelist)) {
+ ab = list_entry(audit_freelist.next,
+ struct audit_buffer, list);
+ list_del(&ab->list);
+ --audit_freelist_count;
+ }
+ spin_unlock_irqrestore(&audit_freelist_lock, flags);
+
+ if (!ab) {
+ ab = kmalloc(sizeof(*ab), gfp_mask);
+ if (!ab)
+ goto err;
+ }
+
+ ab->skb = alloc_skb(AUDIT_BUFSIZ, gfp_mask);
+ if (!ab->skb)
+ goto err;
+
+ ab->ctx = ctx;
+ nlh = (struct nlmsghdr *)skb_put(ab->skb, NLMSG_SPACE(0));
+ nlh->nlmsg_type = type;
+ nlh->nlmsg_flags = 0;
+ nlh->nlmsg_pid = 0;
+ nlh->nlmsg_seq = 0;
+ return ab;
+err:
+ audit_buffer_free(ab);
+ return NULL;
+}
+
+/* Compute a serial number for the audit record. Audit records are
+ * written to user-space as soon as they are generated, so a complete
+ * audit record may be written in several pieces. The timestamp of the
+ * record and this serial number are used by the user-space tools to
+ * determine which pieces belong to the same audit record. The
+ * (timestamp,serial) tuple is unique for each syscall and is live from
+ * syscall entry to syscall exit.
+ *
+ * Atomic values are only guaranteed to be 24-bit, so we count down.
+ *
+ * NOTE: Another possibility is to store the formatted records off the
+ * audit context (for those records that have a context), and emit them
+ * all at syscall exit. However, this could delay the reporting of
+ * significant errors until syscall exit (or never, if the system
+ * halts). */
+unsigned int audit_serial(void)
+{
+ static atomic_t serial = ATOMIC_INIT(0xffffff);
+ unsigned int a, b;
+
+ do {
+ a = atomic_read(&serial);
+ if (atomic_dec_and_test(&serial))
+ atomic_set(&serial, 0xffffff);
+ b = atomic_read(&serial);
+ } while (b != a - 1);
+
+ return 0xffffff - b;
+}
+
+static inline void audit_get_stamp(struct audit_context *ctx,
+ struct timespec *t, unsigned int *serial)
+{
+ if (ctx)
+ auditsc_get_stamp(ctx, t, serial);
+ else {
+ *t = CURRENT_TIME;
+ *serial = audit_serial();
+ }
+}