[Samba] mkdir-dup test flapping

[Douglas Bagnall]

We looked at this some more, and Andrew seemed to understand and wrote
the attached patch.
> 
> We got the logs by forcing smbd to run with -d10 by patching
> file_server/fileserver.c.

The issue appears to be in this call:

3638            /* Ensure there was no race condition. */
3639            if (!check_same_stat(&smb_dname->st, &fsp->fsp_name->st)) {
3640                    samba_start_debugger();
3641                    DEBUG(5,("open_directory: stat struct differs for "
3642                            "directory %s.\n",
3643                            smb_fname_str_dbg(smb_dname)));
3644                    fd_close(fsp);
(gdb) p smb_dname->st
$1 = {st_ex_dev = 64512, st_ex_ino = 44701075, st_ex_mode = 16877,
  st_ex_nlink = 2, st_ex_uid = 50133, st_ex_gid = 50133, st_ex_rdev = 0,
  st_ex_size = 0, st_ex_atime = {tv_sec = 1457488009, tv_nsec = 820161188},
  st_ex_mtime = {tv_sec = 1457488009, tv_nsec = 820161188}, st_ex_ctime = {
    tv_sec = 1457488009, tv_nsec = 820161188}, st_ex_btime = {
    tv_sec = 1457488009, tv_nsec = 820161188},
  st_ex_calculated_birthtime = true, st_ex_blksize = 4096, st_ex_blocks = 8,
  st_ex_flags = 0, st_ex_mask = 0}
(gdb) p fsp->fsp_name->st
$2 = {st_ex_dev = 64512, st_ex_ino = 44701075, st_ex_mode = 16877,
  st_ex_nlink = 2, st_ex_uid = 3000000, st_ex_gid = 65531, st_ex_rdev = 0,
  st_ex_size = 0, st_ex_atime = {tv_sec = 1457488009, tv_nsec = 820161188},
  st_ex_mtime = {tv_sec = 1457488009, tv_nsec = 820161188}, st_ex_ctime = {
    tv_sec = 1457488009, tv_nsec = 820161188}, st_ex_btime = {
    tv_sec = 1457488009, tv_nsec = 820161188},
  st_ex_calculated_birthtime = true, st_ex_blksize = 4096, st_ex_blocks = 8,
  st_ex_flags = 0, st_ex_mask = 0}
(gdb)

where you can see the st_ex_uid and st_ex_gid fields differ:

douglasb at douglasb-desktop:~/src/samba (flap *)$ bin/wbinfo --uid-info=50133
ADDOMAIN/administrator:*:50133:65531::/home/ADDOMAIN/administrator:/bin/false
douglasb at douglasb-desktop:~/src/samba (flap *)$ bin/wbinfo --uid-info=3000000
BUILTIN/administrators:*:3000000:3000000::/home/BUILTIN/administrators:/bin/false

The issue is that after the mkdir, we run:

		} else if (lp_inherit_acls(SNUM(conn))) {
			/* Inherit from parent. Errors here are not fatal. */
			status = inherit_new_acl(fsp);
			if (!NT_STATUS_IS_OK(status)) {

while in the other process that is doing the open of the existing
directory, we do:

					if (SMB_VFS_LSTAT(conn, smb_dname)
							== -1) {
						DEBUG(2, ("Could not stat "
							"directory '%s' just "
							"opened: %s\n",
							smb_fname_str_dbg(
								smb_dname),
							strerror(errno)));
						return map_nt_error_from_unix(
								errno);
					}

And then only a few lines later we do:

    !check_same_stat(&smb_dname->st, &fsp->fsp_name->st)) {

The inherit_new_acl() can change the owner of the directory in the
time it takes between the first stat() and the second one. This is
seen only in the AD DC because of special logic that makes
BUILTIN\Administrators the owner of files created by any
administrative user.

We need to decide if the change in owner is enough reason to refuse
the open(), or if we should just continue.

On the basis that the owner change is not significant, we reworked the
code to do the lstat() after the fstat(), and not compare the owner.

Another way to avoid the flapping would be to run this test as someone
other than Administrator.

Douglas and Andrew