ntfs3: pretend $Extend records as regular files

Since commit af153bb ("vfs: catch invalid modes in may_open()")
requires any inode be one of S_IFDIR/S_IFLNK/S_IFREG/S_IFCHR/S_IFBLK/
S_IFIFO/S_IFSOCK type, use S_IFREG for $Extend records.

Reported-by: syzbot <syzbot+895c23f6917da440ed0d@syzkaller.appspotmail.com>
Closes: https://syzkaller.appspot.com/bug?extid=895c23f6917da440ed0d
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>

Author: Tetsuo Handa

fs/ntfs3/inode.c

@@ -471,6 +471,7 @@ static struct inode *ntfs_read_mft(struct inode *inode,
 		   fname->home.seq == cpu_to_le16(MFT_REC_EXTEND)) {
 		/* Records in $Extend are not a files or general directories. */
 		inode->i_op = &ntfs_file_inode_operations;
+		mode = S_IFREG;
 	} else {
 		err = -EINVAL;
 		goto out;