grub-install: Add backup and restore

Refactor clean_grub_dir() to create a backup of all the files, instead
of just irrevocably removing them as the first action. If available,
register atexit() handler to restore the backup if errors occur before
point of no return, or remove the backup if everything was successful.
If atexit() is not available, the backup remains on disk for manual
recovery.

Some platforms defined a point of no return, i.e. after modules & core
images were updated. Failures from any commands after that stage are
ignored, and backup is cleaned up. For example, on EFI platforms update
is not reverted when efibootmgr fails.

Extra care is taken to ensure atexit() handler is only invoked by the
parent process and not any children forks. Some older GRUB codebases
can invoke parent atexit() hooks from forks, which can mess up the
backup.

This allows safer upgrades of MBR & modules, such that
modules/images/fonts/translations are consistent with MBR in case of
errors. For example accidental grub-install /dev/non-existent-disk
currently clobbers and upgrades modules in /boot/grub, despite not
actually updating any MBR.

This patch only handles backup and restore of files copied to /boot/grub.
This patch does not perform backup (or restoration) of MBR itself or
blocklists. Thus when installing i386-pc platform, corruption may still
occur with MBR and blocklists which will not be attempted to be
automatically recovered.

Also add modinfo.sh and *.efi to the cleanup/backup/restore code path,
to ensure it is also cleaned, backed up and restored.

Signed-off-by: Dimitri John Ledkov <xnox@ubuntu.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

configure.ac

@@ -419,7 +419,7 @@ else
 fi
 
 # Check for functions and headers.
-AC_CHECK_FUNCS(posix_memalign memalign getextmntent)
+AC_CHECK_FUNCS(posix_memalign memalign getextmntent atexit)
 AC_CHECK_HEADERS(sys/param.h sys/mount.h sys/mnttab.h limits.h)
 
 # glibc 2.25 still includes sys/sysmacros.h in sys/types.h but emits deprecation

include/grub/util/install.h

@@ -275,4 +275,25 @@ extern char *grub_install_copy_buffer;
 int
 grub_install_is_short_mbrgap_supported (void);
 
+/*
+ * grub-install-common tries to make backups of modules & auxiliary files,
+ * and restore the backup upon failure to install core.img. There are
+ * platforms with additional actions after modules & core got installed
+ * in place. It is a point of no return, as core.img cannot be reverted
+ * from this point onwards, and new modules should be kept installed.
+ * Before performing these additional actions call grub_set_install_backup_ponr()
+ * to set the grub_install_backup_ponr flag. This way failure to perform
+ * subsequent actions will not result in reverting new modules to the
+ * old ones, e.g. in case efivars updates fails.
+ */
+#ifdef HAVE_ATEXIT
+extern void
+grub_set_install_backup_ponr (void);
+#else
+static inline void
+grub_set_install_backup_ponr (void)
+{
+}
+#endif
+
 #endif

util/grub-install-common.c

@@ -185,38 +185,164 @@ grub_install_mkdir_p (const char *dst)
   free (t);
 }
 
+static int
+strcmp_ext (const char *a, const char *b, const char *ext)
+{
+  char *bsuffix = grub_util_path_concat_ext (1, b, ext);
+  int r = strcmp (a, bsuffix);
+
+  free (bsuffix);
+  return r;
+}
+
+enum clean_grub_dir_mode
+{
+  CLEAN_NEW,
+  CLEAN_BACKUP,
+  CREATE_BACKUP,
+  RESTORE_BACKUP
+};
+
+#ifdef HAVE_ATEXIT
+static size_t backup_dirs_size = 0;
+static char **backup_dirs = NULL;
+static pid_t backup_process = 0;
+static int grub_install_backup_ponr = 0;
+
+void
+grub_set_install_backup_ponr (void)
+{
+  grub_install_backup_ponr = 1;
+}
+#endif
+
 static void
-clean_grub_dir (const char *di)
+clean_grub_dir_real (const char *di, enum clean_grub_dir_mode mode)
 {
   grub_util_fd_dir_t d;
   grub_util_fd_dirent_t de;
+  const char *suffix = "";
+
+  if ((mode == CLEAN_BACKUP) || (mode == RESTORE_BACKUP))
+    suffix = "~";
 
   d = grub_util_fd_opendir (di);
   if (!d)
-    grub_util_error (_("cannot open directory `%s': %s"),
-		     di, grub_util_fd_strerror ());
+    {
+      if (mode == CLEAN_BACKUP)
+	return;
+      grub_util_error (_("cannot open directory `%s': %s"),
+		       di, grub_util_fd_strerror ());
+    }
 
   while ((de = grub_util_fd_readdir (d)))
     {
       const char *ext = strrchr (de->d_name, '.');
-      if ((ext && (strcmp (ext, ".mod") == 0
-		   || strcmp (ext, ".lst") == 0
-		   || strcmp (ext, ".img") == 0
-		   || strcmp (ext, ".mo") == 0)
-	   && strcmp (de->d_name, "menu.lst") != 0)
-	  || strcmp (de->d_name, "efiemu32.o") == 0
-	  || strcmp (de->d_name, "efiemu64.o") == 0)
+
+      if ((ext && (strcmp_ext (ext, ".mod", suffix) == 0
+		   || strcmp_ext (ext, ".lst", suffix) == 0
+		   || strcmp_ext (ext, ".img", suffix) == 0
+		   || strcmp_ext (ext, ".efi", suffix) == 0
+		   || strcmp_ext (ext, ".mo", suffix) == 0)
+	   && strcmp_ext (de->d_name, "menu.lst", suffix) != 0)
+	  || strcmp_ext (de->d_name, "modinfo.sh", suffix) == 0
+	  || strcmp_ext (de->d_name, "efiemu32.o", suffix) == 0
+	  || strcmp_ext (de->d_name, "efiemu64.o", suffix) == 0)
 	{
-	  char *x = grub_util_path_concat (2, di, de->d_name);
-	  if (grub_util_unlink (x) < 0)
-	    grub_util_error (_("cannot delete `%s': %s"), x,
-			     grub_util_fd_strerror ());
-	  free (x);
+	  char *srcf = grub_util_path_concat (2, di, de->d_name);
+
+	  if (mode == CREATE_BACKUP)
+	    {
+	      char *dstf = grub_util_path_concat_ext (2, di, de->d_name, "~");
+
+	      if (grub_util_rename (srcf, dstf) < 0)
+		grub_util_error (_("cannot backup `%s': %s"), srcf,
+				 grub_util_fd_strerror ());
+	      free (dstf);
+	    }
+	  else if (mode == RESTORE_BACKUP)
+	    {
+	      char *dstf = grub_util_path_concat (2, di, de->d_name);
+
+	      dstf[strlen (dstf) - 1] = '\0';
+	      if (grub_util_rename (srcf, dstf) < 0)
+		grub_util_error (_("cannot restore `%s': %s"), dstf,
+				 grub_util_fd_strerror ());
+	      free (dstf);
+	    }
+	  else
+	    {
+	      if (grub_util_unlink (srcf) < 0)
+		grub_util_error (_("cannot delete `%s': %s"), srcf,
+				 grub_util_fd_strerror ());
+	    }
+	  free (srcf);
 	}
     }
   grub_util_fd_closedir (d);
 }
 
+#ifdef HAVE_ATEXIT
+static void
+restore_backup_atexit (void)
+{
+  size_t i;
+
+  /*
+   * Some child inherited atexit() handler, did not clear it, and called it.
+   * Thus skip clean or restore logic.
+   */
+  if (backup_process != getpid ())
+    return;
+
+  for (i = 0; i < backup_dirs_size; i++)
+    {
+      /*
+       * If past point of no return simply clean the backups. Otherwise
+       * cleanup newly installed files, and restore the backups.
+       */
+      if (grub_install_backup_ponr)
+	clean_grub_dir_real (backup_dirs[i], CLEAN_BACKUP);
+      else
+	{
+	  clean_grub_dir_real (backup_dirs[i], CLEAN_NEW);
+	  clean_grub_dir_real (backup_dirs[i], RESTORE_BACKUP);
+	}
+      free (backup_dirs[i]);
+    }
+
+  backup_dirs_size = 0;
+
+  free (backup_dirs);
+}
+
+static void
+append_to_backup_dirs (const char *dir)
+{
+  backup_dirs = xrealloc (backup_dirs, sizeof (char *) * (backup_dirs_size + 1));
+  backup_dirs[backup_dirs_size] = xstrdup (dir);
+  backup_dirs_size++;
+  if (!backup_process)
+    {
+      atexit (restore_backup_atexit);
+      backup_process = getpid ();
+    }
+}
+#else
+static void
+append_to_backup_dirs (const char *dir __attribute__ ((unused)))
+{
+}
+#endif
+
+static void
+clean_grub_dir (const char *di)
+{
+  clean_grub_dir_real (di, CLEAN_BACKUP);
+  clean_grub_dir_real (di, CREATE_BACKUP);
+  append_to_backup_dirs (di);
+}
+
 struct install_list
 {
   int is_default;

util/grub-install.c

@@ -1719,10 +1719,14 @@ main (int argc, char *argv[])
 			
 	/*  Now perform the installation.  */
 	if (install_bootsector)
-	  grub_util_bios_setup (platdir, "boot.img", "core.img",
-				install_drive, force,
-				fs_probe, allow_floppy, add_rs_codes,
-				!grub_install_is_short_mbrgap_supported ());
+	  {
+	    grub_util_bios_setup (platdir, "boot.img", "core.img",
+				  install_drive, force,
+				  fs_probe, allow_floppy, add_rs_codes,
+				  !grub_install_is_short_mbrgap_supported ());
+
+	    grub_set_install_backup_ponr ();
+	  }
 	break;
       }
     case GRUB_INSTALL_PLATFORM_SPARC64_IEEE1275:
@@ -1746,10 +1750,14 @@ main (int argc, char *argv[])
 			
 	/*  Now perform the installation.  */
 	if (install_bootsector)
-	  grub_util_sparc_setup (platdir, "boot.img", "core.img",
-				 install_drive, force,
-				 fs_probe, allow_floppy,
-				 0 /* unused */, 0 /* unused */ );
+	  {
+	    grub_util_sparc_setup (platdir, "boot.img", "core.img",
+				   install_drive, force,
+				   fs_probe, allow_floppy,
+				   0 /* unused */, 0 /* unused */ );
+
+	    grub_set_install_backup_ponr ();
+	  }
 	break;
       }
 
@@ -1776,6 +1784,8 @@ main (int argc, char *argv[])
 	  grub_elf = grub_util_path_concat (2, core_services, "grub.elf");
 	  grub_install_copy_file (imgfile, grub_elf, 1);
 
+	  grub_set_install_backup_ponr ();
+
 	  f = grub_util_fopen (mach_kernel, "a+");
 	  if (!f)
 	    grub_util_error (_("Can't create file: %s"), strerror (errno));
@@ -1878,6 +1888,8 @@ main (int argc, char *argv[])
 	  boot_efi = grub_util_path_concat (2, core_services, "boot.efi");
 	  grub_install_copy_file (imgfile, boot_efi, 1);
 
+	  grub_set_install_backup_ponr ();
+
 	  f = grub_util_fopen (mach_kernel, "r+");
 	  if (!f)
 	    grub_util_error (_("Can't create file: %s"), strerror (errno));
@@ -1916,6 +1928,9 @@ main (int argc, char *argv[])
       {
 	char *dst = grub_util_path_concat (2, efidir, efi_file);
 	grub_install_copy_file (imgfile, dst, 1);
+
+	grub_set_install_backup_ponr ();
+
 	free (dst);
       }
       if (!removable && update_nvram)
@@ -1967,6 +1982,14 @@ main (int argc, char *argv[])
       break;
     }
 
+  /*
+   * Either there are no platform specific code, or it didn't raise
+   * ponr. Raise it here, because usually this is already past point
+   * of no return. If we leave this flag false, at exit all the modules
+   * will be removed from the prefix which would be very confusing.
+   */
+  grub_set_install_backup_ponr ();
+
   fprintf (stderr, "%s\n", _("Installation finished. No error reported."));
 
   /* Free resources.  */

util/grub-mknetdir.c

@@ -159,6 +159,9 @@ process_input_dir (const char *input_dir, enum grub_install_plat platform)
   grub_install_make_image_wrap (input_dir, prefix, output,
 				0, load_cfg,
 				targets[platform].mkimage_target, 0);
+
+  grub_set_install_backup_ponr ();
+
   grub_install_pop_module ();
 
   /* TRANSLATORS: First %s is replaced by platform name. Second one by filename.  */

util/grub-mkrescue.c

@@ -530,6 +530,9 @@ main (int argc, char *argv[])
 			       boot_grub, plat);
       source_dirs[plat] = xstrdup (grub_install_source_directory);
     }
+
+  grub_set_install_backup_ponr ();
+
   if (system_area == SYS_AREA_AUTO || grub_install_source_directory)
     {
       if (source_dirs[GRUB_INSTALL_PLATFORM_I386_PC]

util/grub-mkstandalone.c

@@ -318,6 +318,8 @@ main (int argc, char *argv[])
   grub_install_copy_files (grub_install_source_directory,
 			   boot_grub, plat);
 
+  grub_set_install_backup_ponr ();
+
   char *memdisk_img = grub_util_make_temporary_file ();
 
   memdisk = grub_util_fopen (memdisk_img, "wb");