crontab: remove useless gid swapping

[Todd C. Miller]

The only place we really need to drop setgid is when opening an
arbitrary file, e.g. "crontab /foo/bar", which prevents the user
from viewing other people's crontab files.  Now that TMPDIR support
is gone things are a bit simpler...

 - todd

Index: crontab.c
===================================================================
RCS file: /cvs/src/usr.sbin/cron/crontab.c,v
retrieving revision 1.79
diff -u -p -u -r1.79 crontab.c
--- crontab.c   2 Nov 2015 20:09:02 -0000       1.79
+++ crontab.c   2 Nov 2015 20:21:48 -0000
@@ -314,15 +314,7 @@ edit_cmd(void)
                fprintf(stderr, "path too long\n");
                goto fatal;
        }
-       if (setegid(user_gid) < 0) {
-               perror("setegid(user_gid)");
-               exit(EXIT_FAILURE);
-       }
        t = mkstemp(Filename);
-       if (setegid(crontab_gid) < 0) {
-               perror("setegid(crontab_gid)");
-               exit(EXIT_FAILURE);
-       }
        if (t == -1) {
                perror(Filename);
                goto fatal;
@@ -347,15 +339,7 @@ edit_cmd(void)
                fprintf(stderr, "%s: error while writing new crontab to %s\n",
                        ProgramName, Filename);
  fatal:
-               if (setegid(user_gid) < 0) {
-                       perror("setegid(user_gid)");
-                       exit(EXIT_FAILURE);
-               }
                unlink(Filename);
-               if (setegid(crontab_gid) < 0) {
-                       perror("setegid(crontab_gid)");
-                       exit(EXIT_FAILURE);
-               }
                exit(EXIT_FAILURE);
        }
 
@@ -376,19 +360,11 @@ edit_cmd(void)
                goto fatal;
        }
        if (timespeccmp(&ts[1], &statbuf.st_mtim, ==)) {
-               if (setegid(user_gid) < 0) {
-                       perror("setegid(user_gid)");
-                       exit(EXIT_FAILURE);
-               }
                if (lstat(Filename, &xstatbuf) == 0 &&
                    statbuf.st_ino != xstatbuf.st_ino) {
                        fprintf(stderr, "%s: crontab temp file moved, editor "
                           "may create backup files improperly\n", ProgramName);
                }
-               if (setegid(crontab_gid) < 0) {
-                       perror("setegid(crontab_gid)");
-                       exit(EXIT_FAILURE);
-               }
                fprintf(stderr, "%s: no changes made to crontab\n",
                        ProgramName);
                goto remove;
@@ -429,15 +405,7 @@ edit_cmd(void)
                goto fatal;
        }
  remove:
-       if (setegid(user_gid) < 0) {
-               perror("setegid(user_gid)");
-               exit(EXIT_FAILURE);
-       }
        unlink(Filename);
-       if (setegid(crontab_gid) < 0) {
-               perror("setegid(crontab_gid)");
-               exit(EXIT_FAILURE);
-       }
  done:
        log_it(RealUser, Pid, "END EDIT", User);
 }