From d7d362995aa0cb8905c8d5c2a2a4c305d2ffff80 Mon Sep 17 00:00:00 2001
From: Ondrej Holy <oholy@redhat.com>
Date: Thu, 23 May 2019 10:33:30 +0200
Subject: [PATCH] admin: Use fsuid to ensure correct file ownership

Files created over admin backend should be owned by root, but they are
owned by the user itself. This is because the daemon drops the uid to
make dbus connection work. Use fsuid and euid to fix this issue.

Closes: https://gitlab.gnome.org/GNOME/gvfs/issues/21
---
 daemon/gvfsbackendadmin.c | 29 +++++++----------------------
 1 file changed, 7 insertions(+), 22 deletions(-)

diff --git a/daemon/gvfsbackendadmin.c b/daemon/gvfsbackendadmin.c
index a74d09cf..32b51b1a 100644
--- a/daemon/gvfsbackendadmin.c
+++ b/daemon/gvfsbackendadmin.c
@@ -157,19 +157,6 @@ complete_job (GVfsJob *job,
   g_vfs_job_succeeded (job);
 }
 
-static void
-fix_file_info (GFileInfo *info)
-{
-  /* Override read/write flags, since the above call will use access()
-   * to determine permissions, which does not honor our privileged
-   * capabilities.
-   */
-  g_file_info_set_attribute_boolean (info, G_FILE_ATTRIBUTE_ACCESS_CAN_READ, TRUE);
-  g_file_info_set_attribute_boolean (info, G_FILE_ATTRIBUTE_ACCESS_CAN_WRITE, TRUE);
-  g_file_info_set_attribute_boolean (info, G_FILE_ATTRIBUTE_ACCESS_CAN_DELETE, TRUE);
-  g_file_info_set_attribute_boolean (info, G_FILE_ATTRIBUTE_ACCESS_CAN_RENAME, TRUE);
-}
-
 static void
 do_query_info (GVfsBackend *backend,
                GVfsJobQueryInfo *query_info_job,
@@ -195,7 +182,6 @@ do_query_info (GVfsBackend *backend,
   if (error != NULL)
     goto out;
 
-  fix_file_info (real_info);
   g_file_info_copy_into (real_info, info);
   g_object_unref (real_info);
 
@@ -220,7 +206,6 @@ do_query_info_on_read (GVfsBackend *backend,
   if (error != NULL)
     goto out;
 
-  fix_file_info (real_info);
   g_file_info_copy_into (real_info, info);
   g_object_unref (real_info);
 
@@ -245,7 +230,6 @@ do_query_info_on_write (GVfsBackend *backend,
   if (error != NULL)
     goto out;
 
-  fix_file_info (real_info);
   g_file_info_copy_into (real_info, info);
   g_object_unref (real_info);
 
@@ -977,14 +961,15 @@ acquire_caps (uid_t uid)
   struct __user_cap_header_struct hdr;
   struct __user_cap_data_struct data;
 
-  /* Tell kernel not clear capabilities when dropping root */
-  if (prctl (PR_SET_KEEPCAPS, 1, 0, 0, 0) < 0)
-    g_error ("prctl(PR_SET_KEEPCAPS) failed");
-
-  /* Drop root uid, but retain the required permitted caps */
-  if (setuid (uid) < 0)
+  /* Set euid to user to make dbus work */
+  if (seteuid (uid) < 0)
     g_error ("unable to drop privs");
 
+  /* Set fsuid to still behave like root when working with files */
+  setfsuid (0);
+  if (setfsuid (-1) != 0)
+   g_error ("setfsuid failed");
+
   memset (&hdr, 0, sizeof(hdr));
   hdr.version = _LINUX_CAPABILITY_VERSION;
 
-- 
2.23.0