smb3: fix incorrect mode displayed for read-only files

Commands like "chmod 0444" mark a file readonly via the attribute flag
(when mapping of mode bits into the ACL are not set, or POSIX extensions
are not negotiated), but they were not reported correctly for stat of
directories (they were reported ok for files and for "ls").  See example
below:

    root:~# ls /mnt2 -l
    total 12
    drwxr-xr-x 2 root root         0 Sep 21 18:03 normaldir
    -rwxr-xr-x 1 root root         0 Sep 21 23:24 normalfile
    dr-xr-xr-x 2 root root         0 Sep 21 17:55 readonly-dir
    -r-xr-xr-x 1 root root 209716224 Sep 21 18:15 readonly-file
    root:~# stat -c %a /mnt2/readonly-dir
    755
    root:~# stat -c %a /mnt2/readonly-file
    555

This fixes the stat of directories when ATTR_READONLY is set
(in cases where the mode can not be obtained other ways).

    root:~# stat -c %a /mnt2/readonly-dir
    555

Cc: stable@vger.kernel.org
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/smb/client/inode.c

@@ -834,10 +834,6 @@ static void cifs_open_info_to_fattr(struct cifs_fattr *fattr,
 		fattr->cf_mode = S_IFREG | cifs_sb->ctx->file_mode;
 		fattr->cf_dtype = DT_REG;
 
-		/* clear write bits if ATTR_READONLY is set */
-		if (fattr->cf_cifsattrs & ATTR_READONLY)
-			fattr->cf_mode &= ~(S_IWUGO);
-
 		/*
 		 * Don't accept zero nlink from non-unix servers unless
 		 * delete is pending.  Instead mark it as unknown.
@@ -850,6 +846,10 @@ static void cifs_open_info_to_fattr(struct cifs_fattr *fattr,
 		}
 	}
 
+	/* clear write bits if ATTR_READONLY is set */
+	if (fattr->cf_cifsattrs & ATTR_READONLY)
+		fattr->cf_mode &= ~(S_IWUGO);
+
 out_reparse:
 	if (S_ISLNK(fattr->cf_mode)) {
 		if (likely(data->symlink_target))
@@ -1267,11 +1267,14 @@ static int cifs_get_fattr(struct cifs_open_info_data *data,
 				 __func__, rc);
 			goto out;
 		}
-	}
-
-	/* fill in remaining high mode bits e.g. SUID, VTX */
-	if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_UNX_EMUL)
+	} else if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_UNX_EMUL)
+		/* fill in remaining high mode bits e.g. SUID, VTX */
 		cifs_sfu_mode(fattr, full_path, cifs_sb, xid);
+	else if (!(tcon->posix_extensions))
+		/* clear write bits if ATTR_READONLY is set */
+		if (fattr->cf_cifsattrs & ATTR_READONLY)
+			fattr->cf_mode &= ~(S_IWUGO);
+
 
 	/* check for Minshall+French symlinks */
 	if (cifs_sb->mnt_cifs_flags & CIFS_MOUNT_MF_SYMLINKS) {