fs/ntfs3: Additional check in ntfs_file_release

Reported-by: syzbot+8c652f14a0fde76ff11d@syzkaller.appspotmail.com
Signed-off-by: Konstantin Komarov <almaz.alexandrovich@paragon-software.com>

Author: aalexandrovich

fs/ntfs3/file.c

@@ -1314,7 +1314,14 @@ static int ntfs_file_release(struct inode *inode, struct file *file)
 	/* If we are last writer on the inode, drop the block reservation. */
 	if (sbi->options->prealloc &&
 	    ((file->f_mode & FMODE_WRITE) &&
-	     atomic_read(&inode->i_writecount) == 1)) {
+	     atomic_read(&inode->i_writecount) == 1)
+	   /*
+	    * The only file when inode->i_fop = &ntfs_file_operations and
+	    * init_rwsem(&ni->file.run_lock) is not called explicitly is MFT.
+	    *
+	    * Add additional check here.
+	    */
+	    && inode->i_ino != MFT_REC_MFT) {
 		ni_lock(ni);
 		down_write(&ni->file.run_lock);