Only mount non-empty directories for cgroups (miklos.szegedi@cloudera.com via rkanter)

(cherry picked from commit 0838fe833738e04f5e6f6408e97866d77bebbf30)

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-nodemanager/src/main/native/container-executor/impl/container-executor.c

@@ -2379,6 +2379,28 @@ void chown_dir_contents(const char *dir_path, uid_t uid, gid_t gid) {
   free(path_tmp);
 }
 
+int is_empty(char *target_dir) {
+  DIR *dir = NULL;
+  struct dirent *entry = NULL;
+  dir = opendir(target_dir);
+  if (!dir) {
+    fprintf(LOGFILE, "Could not open directory %s - %s\n", target_dir,
+            strerror(errno));
+    return 0;
+  }
+  while ((entry = readdir(dir)) != NULL) {
+    if (strcmp(entry->d_name, ".") == 0) {
+      continue;
+    }
+    if (strcmp(entry->d_name, "..") == 0) {
+      continue;
+    }
+    fprintf(LOGFILE, "Directory is not empty %s\n", target_dir);
+    return 0;
+  }
+  return 1;
+}
+
 /**
  * Mount a cgroup controller at the requested mount point and create
  * a hierarchy for the Hadoop NodeManager to manage.
@@ -2413,7 +2435,13 @@ int mount_cgroup(const char *pair, const char *hierarchy) {
     result = -1;
   } else {
     if (strstr(mount_path, "..") != NULL) {
-      fprintf(LOGFILE, "Unsupported cgroup mount path detected.\n");
+      fprintf(LOGFILE, "Unsupported cgroup mount path detected. %s\n",
+          mount_path);
+      result = INVALID_COMMAND_PROVIDED;
+      goto cleanup;
+    }
+    if (!is_empty(mount_path)) {
+      fprintf(LOGFILE, "cgroup mount path is not empty. %s\n", mount_path);
       result = INVALID_COMMAND_PROVIDED;
       goto cleanup;
     }

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-nodemanager/src/main/native/container-executor/test/test-container-executor.c

@@ -1203,6 +1203,23 @@ void test_trim_function() {
   free(trimmed);
 }
 
+void test_is_empty() {
+  printf("\nTesting is_empty function\n");
+  if (is_empty("/")) {
+    printf("FAIL: / should not be empty\n");
+    exit(1);
+  }
+  if (is_empty("/tmp/2938rf2983hcqnw8ud/noexist")) {
+    printf("FAIL: /tmp/2938rf2983hcqnw8ud/noexist should not exist\n");
+    exit(1);
+  }
+  mkdir("/tmp/2938rf2983hcqnw8ud/emptydir", S_IRWXU);
+  if (!is_empty("/tmp/2938rf2983hcqnw8ud/emptydir")) {
+    printf("FAIL: /tmp/2938rf2983hcqnw8ud/emptydir be empty\n");
+    exit(1);
+  }
+}
+
 // This test is expected to be executed either by a regular
 // user or by root. If executed by a regular user it doesn't
 // test all the functions that would depend on changing the
@@ -1264,6 +1281,9 @@ int main(int argc, char **argv) {
 
   printf("\nStarting tests\n");
 
+  printf("\ntest_is_empty()\n");
+  test_is_empty();
+
   printf("\nTesting recursive_unlink_children()\n");
   test_recursive_unlink_children();