Added database protection with setuid.

Added the initial support for the database protection with the setuid
mechanism. In the beginning the program creates(or opens) the database
as a special user, and then switches to the real uid and functions
normally.

src/main.c

@@ -10,6 +10,8 @@
   See the file LICENSE.
 */
 
+#include <sys/types.h>
+#include <unistd.h>
 #define FUSE_USE_VERSION 31
 
 #define _GNU_SOURCE
@@ -28,17 +30,17 @@ const char *mountpoint = NULL;
 int main(int argc, char *argv[]) {
   umask(0);
 
-  mountpoint = realpath(argv[argc - 1], NULL);
+  int ret = init_ui_socket();
-
-  int ret = source_init(mountpoint);
   if (ret != 0) {
-    perror("source_init");
+    fprintf(stderr, "Could not initalize ui-socket.\n");
     exit(EXIT_FAILURE);
   }
 
-  ret = init_ui_socket();
+  mountpoint = realpath(argv[argc - 1], NULL);
+
+  ret = source_init(mountpoint);
   if (ret != 0) {
-    fprintf(stderr, "Could not initalize ui-socket.\n");
+    perror("source_init");
     exit(EXIT_FAILURE);
   }
 

src/perm_permissions_table.c

@@ -1,10 +1,16 @@
 #include "perm_permissions_table.h"
 #include "process_info.h"
+#include <fcntl.h>
+#include <pthread.h>
 #include <sqlite3.h>
 #include <stddef.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
+#include <sys/fsuid.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
 
 sqlite3 *perm_database = NULL;
 const char *const table_name = "permissions";
@@ -12,6 +18,38 @@ const char *const table_name = "permissions";
 const int column_count = 2;
 const char *const schema[] = {"executable", "filename"};
 const char *const types[] = {"TEXT", "TEXT"};
+uid_t ruid, euid, current_pid;
+pthread_mutex_t uid_switch = PTHREAD_MUTEX_INITIALIZER;
+
+void set_db_fsuid() {
+  pthread_mutex_lock(&uid_switch);
+  if (current_pid == ruid)
+    return;
+
+  int status = -1;
+
+  status = setfsuid(ruid);
+  if (status < 0) {
+    fprintf(stderr, "Couldn't set uid to %d.\n", ruid);
+    exit(status);
+  }
+  pthread_mutex_unlock(&uid_switch);
+}
+
+void set_real_fsuid() {
+  pthread_mutex_lock(&uid_switch);
+  if (current_pid == ruid)
+    return;
+
+  int status = -1;
+
+  status = setfsuid(ruid);
+  if (status < 0) {
+    fprintf(stderr, "Couldn't set uid to %d.\n", euid);
+    exit(status);
+  }
+  pthread_mutex_unlock(&uid_switch);
+}
 
 static int check_table_col_schema(void *notused, int argc, char **argv,
                                   char **colname) {
@@ -21,15 +59,16 @@ static int check_table_col_schema(void *notused, int argc, char **argv,
     fprintf(stderr, "Unexpected amount of arguments given to the callback.\n");
     return 1;
   }
-  int i = atoi(argv[0]);
+  int column_num = atoi(argv[0]);
-  if (i >= column_count) {
+  if (column_num >= column_count) {
     fprintf(stderr, "Table contains more columns than expected.\n");
     return 1;
   }
-  if (strcmp(schema[i], argv[1]) == 0 && strcmp(types[i], argv[2]) == 0) {
+  if (strcmp(schema[column_num], argv[1]) == 0 &&
+      strcmp(types[column_num], argv[2]) == 0) {
     return 0;
   }
-  fprintf(stderr, "Column %d does not conform to the schema.\n", i);
+  fprintf(stderr, "Column %d does not conform to the schema.\n", column_num);
   return 1;
 }
 
@@ -101,14 +140,28 @@ int ensure_database_schema() {
  * @return: 0 on success, -1 on failure
  */
 int init_perm_permissions_table(const char *db_filename) {
+  // we don't want the group and others to access the db
+  umask(0077);
+  ruid = getuid();
+  euid = geteuid();
+  fprintf(stderr, "Running with uid: %d, gid: %d\n", euid, getegid());
+
   if (sqlite3_open(db_filename, &perm_database)) {
     perror("Can't open permanent permissions database:");
     return -1;
   }
+  umask(0);
   if (ensure_database_schema()) {
     fprintf(stderr, "Database schema is not correct.\n");
     return -1;
   }
+
+  int status = seteuid(ruid);
+  if (status < 0) {
+    fprintf(stderr, "Couldn't set euid to ruid during database setup.\n");
+    exit(status);
+  }
+
   return 0;
 }
 

src/sourcefs.c

@@ -33,6 +33,8 @@ int source_init(const char *root_path) {
   int root_fd = open(root_path, O_PATH);
 
   if (root_fd == -1) {
+    fprintf(stderr, "Could not initialize source file system at %s", root_path);
+    perror("");
     return -1;
   }
 

test/test.bash

@@ -16,9 +16,23 @@ PATH="$(realpath ./mock/):$PATH"
 # mount the filesystem
 
 echo "Run $(date -u +%Y-%m-%dT%H:%M:%S) "
+if [[ $1 == "--setuid" ]]; then
+  echo "Setting the setuid bit..."
+  echo "root privilieges are required to create a special user and set correct ownership of the executable."
+  id -u icfs &>/dev/null || sudo useradd --system --user-group icfs
+  sudo chown icfs: ../build/icfs && sudo chmod 4777 ../build/icfs
+  chmod g+w . # needed for icfs to be able to create the database
+  echo "Valgrind will not be used due to setuid compatibility issues."
+  ../build/icfs -o default_permissions ./protected &
+  sleep 1
+else
+  echo "Database protection will not be tested due to the lack of setuid capabilites."
+  echo "To test it, run this script with '--setuid'."
   valgrind -s ../build/icfs -o default_permissions ./protected &
-
   sleep 5
+fi
+
+#valgrind -s ../build/icfs -o default_permissions ./protected &
 
 # WARN: please don't use `>` or `>>` operators. They force **this script** to open the file, **not the program you are trying to run**. This is probably not what you mean when you want to test a specific program's access.
 # WARN: avoid using touch, since it generates errors because setting times is not implemented in icfs **yet**.