tar: fix 1.23 Solaris regression related to PRIV_SYS_LINKDIR

The idea was suggested by Petr Sumbera in the thread starting here:
http://lists.gnu.org/archive/html/bug-tar/2010-08/msg00000.html
* src/extract.c (set_mode): Save the errno of the chmod that
failed, for the benefit of chmod_error_details.  Do not bother
retrying chmod unless the mode suggests setuid is the issue.
(extract_archive): Remove redundant call to priv_set_remove_linkdir.
* src/system.c: Include priv-set.h.
(sys_spawn_shell, sys_child_open_for_compress):
(sys_child_open_for_uncompress, sys_exec_command):
(sys_exec_info_script, sys_exec_checkpoint_script):
Invoke priv_set_restore_linkdir before execv or execlp, so that
the subprocess has the same privileges that tar originally did.

src/extract.c

@@ -144,7 +144,7 @@ set_mode (char const *file_name,
 	  char typeflag)
 {
   mode_t mode;
-  bool failed;
+  int chmod_errno;
 
   if (0 < same_permissions_option
       && permstatus != INTERDIR_PERMSTATUS)
@@ -187,18 +187,24 @@ set_mode (char const *file_name,
       mode = cur_info->st_mode ^ invert_permissions;
     }
 
-  failed = chmod (file_name, mode) != 0;
-  if (failed && errno == EPERM)
+  chmod_errno = chmod (file_name, mode) == 0 ? 0 : errno;
+  if (chmod_errno == EPERM && (mode & S_ISUID) != 0)
     {
-      /* On Solaris, chmod may fail if we don't have PRIV_ALL.  */
+      /* On Solaris, chmod may fail if we don't have PRIV_ALL, because
+	 setuid-root files would otherwise be a backdoor.  See
+	 http://opensolaris.org/jive/thread.jspa?threadID=95826
+	 (2009-09-03).  */
       if (priv_set_restore_linkdir () == 0)
 	{
-	  failed = chmod (file_name, mode) != 0;
+	  chmod_errno = chmod (file_name, mode) == 0 ? 0 : errno;
 	  priv_set_remove_linkdir ();
 	}
     }
-  if (failed)
-    chmod_error_details (file_name, mode);
+  if (chmod_errno)
+    {
+      errno = chmod_errno;
+      chmod_error_details (file_name, mode);
+    }
 }
 
 /* Check time after successfully setting FILE_NAME's time stamp to T.  */
@@ -1271,9 +1277,6 @@ extract_archive (void)
 
   fatal_exit_hook = extract_finish;
 
-  /* Try to disable the ability to unlink a directory.  */
-  priv_set_remove_linkdir ();
-
   set_next_block_after (current_header);
 
   if (!current_stat_info.file_name[0]

src/system.c

@@ -1,7 +1,7 @@
 /* System-dependent calls for tar.
 
    Copyright (C) 2003, 2004, 2005, 2006, 2007,
-   2008 Free Software Foundation, Inc.
+   2008, 2010 Free Software Foundation, Inc.
 
    This program is free software; you can redistribute it and/or modify it
    under the terms of the GNU General Public License as published by the
@@ -20,6 +20,7 @@
 #include <system.h>
 
 #include "common.h"
+#include <priv-set.h>
 #include <rmt.h>
 #include <signal.h>
 
@@ -192,6 +193,7 @@ sys_spawn_shell (void)
   child = xfork ();
   if (child == 0)
     {
+      priv_set_restore_linkdir ();
       execlp (shell, "-sh", "-i", (char *) 0);
       exec_fatal (shell);
     }
@@ -362,6 +364,7 @@ sys_child_open_for_compress (void)
 	    }
 	  xdup2 (archive, STDOUT_FILENO);
 	}
+      priv_set_restore_linkdir ();
       execlp (use_compress_program_option, use_compress_program_option, NULL);
       exec_fatal (use_compress_program_option);
     }
@@ -379,6 +382,7 @@ sys_child_open_for_compress (void)
 
       xdup2 (child_pipe[PWRITE], STDOUT_FILENO);
       xclose (child_pipe[PREAD]);
+      priv_set_restore_linkdir ();
       execlp (use_compress_program_option, use_compress_program_option,
 	      (char *) 0);
       exec_fatal (use_compress_program_option);
@@ -496,6 +500,7 @@ sys_child_open_for_uncompress (void)
       if (archive < 0)
 	open_fatal (archive_name_array[0]);
       xdup2 (archive, STDIN_FILENO);
+      priv_set_restore_linkdir ();
       execlp (use_compress_program_option, use_compress_program_option,
 	      "-d", (char *) 0);
       exec_fatal (use_compress_program_option);
@@ -514,6 +519,7 @@ sys_child_open_for_uncompress (void)
 
       xdup2 (child_pipe[PREAD], STDIN_FILENO);
       xclose (child_pipe[PWRITE]);
+      priv_set_restore_linkdir ();
       execlp (use_compress_program_option, use_compress_program_option,
 	      "-d", (char *) 0);
       exec_fatal (use_compress_program_option);
@@ -702,6 +708,7 @@ sys_exec_command (char *file_name, int typechar, struct tar_stat_info *st)
   argv[2] = to_command_option;
   argv[3] = NULL;
 
+  priv_set_restore_linkdir ();
   execv ("/bin/sh", argv);
 
   exec_fatal (file_name);
@@ -816,6 +823,7 @@ sys_exec_info_script (const char **archive_name, int volume_number)
   argv[2] = (char *) info_script_option;
   argv[3] = NULL;
 
+  priv_set_restore_linkdir ();
   execv (argv[0], argv);
 
   exec_fatal (info_script_option);
@@ -863,6 +871,7 @@ sys_exec_checkpoint_script (const char *script_name,
   argv[2] = (char *) script_name;
   argv[3] = NULL;
 
+  priv_set_restore_linkdir ();
   execv (argv[0], argv);
 
   exec_fatal (script_name);