Winbind patch fixes broken client. Please have a look.

[Hannes Schmidt]

Even if this is complete crap, I would appreciate any feedback saying so.

A couple of days ago I posted a problem report to the samba list with some
diagnostics. I seem to have found a
solution on my own and provide a patch here. The problem is related to the
fact that the winbind client code in
libnss_winbind.so leaves the handle to the winbind pipe open, for obvious
reasons. This is perfectly ok, but some
programs get confused if this handle is 0,1 or 2, which they expect to be a
handle to a different file. The patch
makes the winbind client (libnss_winbind.so) code more robust.

Consider the following fragment of broken application code.

if( fork() == 0 ) {
    /* child */
    close( 0 );             /* next open() will return 0 (stdin) */
    getpwent(...);        /* pid changed, so wb_common.c will re-open the
pipe to winbindd, the handle will be 0 */
    fd = open( ... );     /* returned fd is *not* 0 although the code below
assumes this */
    execve( ... );         /* executed program reads from stdin which -
unintentionally - is the winbind pipe */
} else {
    /* parent */
    ...
}

Obviously, this code is broken and could be easily fixed by doing the
getpwent() before the close(). Unfortunately
the version of cron installed on my system is broken in a more complex but
similar way. There is probably more
broken code like this in other standard unix software, especially since it's
such a subtle mistake.

The provided patch to wb_common.c makes sure that the handle to the winbindd
pipe is not 0, 1 or 2.

*** /root/samba-2.2.5/source/nsswitch/wb_common.c Wed Jun 19 03:13:44 2002
--- wb_common.c Thu Jul 25 16:36:39 2002
***************
*** 94,99 ****
--- 94,120 ----
   }
  }

+ /* Returns a duplicate of the given file descriptor that is guranteed
+    not to be 0, 1 or 2 (stdin, stdout or stderr respectively), unless
+    an error occurs. If the given fd is invalid, it will be returned
+    unchanged. If a different error occurs, the returned file handle
+    will still be valid but it may be 0, 1 or 2. If a valid file
+    handle is returned and the returned handle is different to the
+    original one, the original one will be closed. If dup() is broken,
+    this function might never return. */
+
+ int make_nonstd_fd(int fd)
+ {
+  int saved_fd;
+  if (0 >= fd && fd <= 2) {
+      fd = dup(saved_fd = fd);
+      if (fd == -1) return saved_fd;
+      fd = make_nonstd_fd(fd);
+      close(saved_fd);
+  }
+  return fd;
+ }
+
  /* Connect to winbindd socket */

  int winbind_open_pipe_sock(void)
***************
*** 158,164 ****
   if ((winbindd_fd = socket(AF_UNIX, SOCK_STREAM, 0)) == -1) {
    return -1;
   }
!
   if (connect(winbindd_fd, (struct sockaddr *)&sunaddr,
        sizeof(sunaddr)) == -1) {
    close_sock();
--- 179,188 ----
   if ((winbindd_fd = socket(AF_UNIX, SOCK_STREAM, 0)) == -1) {
    return -1;
   }
!
!  winbindd_fd = make_nonstd_fd( winbindd_fd );
!
!
   if (connect(winbindd_fd, (struct sockaddr *)&sunaddr,
        sizeof(sunaddr)) == -1) {
    close_sock();
***************
*** 167,172 ****
--- 191,197 ----

   return winbindd_fd;
  }
+

  /* Write data to winbindd socket */