* fileio.c (Fcopy_file): Adjust mode if fchown fails. (Bug#9002)

If fchown fails to set both uid and gid, try to set just gid,
as that is sometimes allowed.  Adjust the file's mode to eliminate
setuid or setgid bits that are inappropriate if fchown fails.

src/ChangeLog

+2011-07-18  Paul Eggert  <eggert@cs.ucla.edu>
+
+	* fileio.c (Fcopy_file): Adjust mode if fchown fails.  (Bug#9002)
+	If fchown fails to set both uid and gid, try to set just gid,
+	as that is sometimes allowed.  Adjust the file's mode to eliminate
+	setuid or setgid bits that are inappropriate if fchown fails.
+
 2011-07-18  Stefan Monnier  <monnier@iro.umontreal.ca>
 
 	* xdisp.c (next_element_from_string, next_element_from_buffer): Use EQ

src/fileio.c

@@ -38,8 +38,6 @@ along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
 #include <selinux/context.h>
 #endif
 
-#include <ignore-value.h>
-
 #include "lisp.h"
 #include "intervals.h"
 #include "buffer.h"
@@ -1961,9 +1959,21 @@ on the system, we copy the SELinux context of FILE to NEWNAME.  */)
      owner and group.  */
   if (input_file_statable_p)
     {
+      int mode_mask = 07777;
       if (!NILP (preserve_uid_gid))
-	ignore_value (fchown (ofd, st.st_uid, st.st_gid));
-      if (fchmod (ofd, st.st_mode & 07777) != 0)
+	{
+	  /* Attempt to change owner and group.  If that doesn't work
+	     attempt to change just the group, as that is sometimes allowed.
+	     Adjust the mode mask to eliminate setuid or setgid bits
+	     that are inappropriate if the owner and group are wrong.  */
+	  if (fchown (ofd, st.st_uid, st.st_gid) != 0)
+	    {
+	      mode_mask &= ~06000;
+	      if (fchown (ofd, -1, st.st_gid) == 0)
+		mode_mask |= 02000;
+	    }
+	}
+      if (fchmod (ofd, st.st_mode & mode_mask) != 0)
 	report_file_error ("Doing chmod", Fcons (newname, Qnil));
     }
 #endif	/* not MSDOS */