Added garbage collection to the temporary permission table.

src/temp_permissions_table.c

@@ -16,6 +16,8 @@
 #include <stdio.h>
 #include <string.h>
 #include <sys/types.h>
+#include <time.h>
+#include <unistd.h>
 
 struct temp_process_permissions {
   // yes, this is a correct type for start time in jiffies (see
@@ -27,6 +29,8 @@ struct temp_process_permissions {
 
 map(pid_t, struct temp_process_permissions) temp_permissions_table;
 pthread_mutex_t temp_permissions_table_lock;
+pthread_t gc_thread;
+int is_gc_active = 0;
 
 /**
  * Function to get the process creation time (in jiffies) from the proc
@@ -72,6 +76,47 @@ unsigned long long get_process_creation_time(pid_t pid) {
   return creation_time;
 }
 
+int is_valid(pid_t pid, struct temp_process_permissions *entry) {
+  unsigned long long creation_time = get_process_creation_time(pid);
+  if (creation_time == 0) {
+    return 0;
+  }
+
+  if (creation_time != entry->creation_time) {
+    return 0;
+  }
+
+  return 1;
+}
+
+void *garbage_collector(void *arg) {
+  (void)arg;
+
+  while (is_gc_active) {
+    sleep(10);
+    pthread_mutex_lock(&temp_permissions_table_lock);
+
+    vec(pid_t) blacklist;
+    init(&blacklist);
+
+    for_each(&temp_permissions_table, pid, entry) {
+      if (!is_valid(*pid, entry)) {
+        push(&blacklist, *pid);
+        cleanup(&(entry->allowed_files));
+        cleanup(&(entry->denied_files));
+      }
+    }
+
+    for_each(&blacklist, pid) { erase(&temp_permissions_table, *pid); }
+
+    cleanup(&blacklist);
+
+    pthread_mutex_unlock(&temp_permissions_table_lock);
+  }
+
+  return NULL;
+}
+
 /**
  * Initializes the temporary permissions table.
  *
@@ -82,6 +127,18 @@ int init_temp_permissions_table(void) {
   init(&temp_permissions_table);
   return 0;
 }
+/**
+ * Starts the temporary permissions table garbage_collector.
+ *
+ * @return: 0 on success, -1 on failure (e.g. ENOMEM)
+ */
+int init_garbage_collector(void) {
+  is_gc_active = 1;
+  if (pthread_create(&gc_thread, NULL, garbage_collector, NULL) != 0) {
+    return -1;
+  }
+  return 0;
+}
 
 /**
  * Destroys the temporary permissions table.
@@ -91,6 +148,11 @@ int init_temp_permissions_table(void) {
  * screwed.
  */
 void destroy_temp_permissions_table(void) {
+  if (is_gc_active) {
+    is_gc_active = 0;
+    pthread_join(gc_thread, NULL);
+  }
+
   // free the memory allocated for the table
   for_each(&temp_permissions_table, entry) {
     for_each(&entry->allowed_files, allowed_file) { free(*allowed_file); }