smb3: missing inode locks in punch hole

smb3 fallocate punch hole was not grabbing the inode or filemap_invalidate
locks so could have race with pagemap reinstantiating the page.

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

fs/cifs/smb2ops.c

@@ -3384,7 +3384,7 @@ static long smb3_zero_range(struct file *file, struct cifs_tcon *tcon,
 static long smb3_punch_hole(struct file *file, struct cifs_tcon *tcon,
 			    loff_t offset, loff_t len)
 {
-	struct inode *inode;
+	struct inode *inode = file_inode(file);
 	struct cifsFileInfo *cfile = file->private_data;
 	struct file_zero_data_information fsctl_buf;
 	long rc;
@@ -3393,14 +3393,12 @@ static long smb3_punch_hole(struct file *file, struct cifs_tcon *tcon,
 
 	xid = get_xid();
 
-	inode = d_inode(cfile->dentry);
-
+	inode_lock(inode);
 	/* Need to make file sparse, if not already, before freeing range. */
 	/* Consider adding equivalent for compressed since it could also work */
 	if (!smb2_set_sparse(xid, tcon, cfile, inode, set_sparse)) {
 		rc = -EOPNOTSUPP;
-		free_xid(xid);
-		return rc;
+		goto out;
 	}
 
 	filemap_invalidate_lock(inode->i_mapping);
@@ -3420,8 +3418,10 @@ static long smb3_punch_hole(struct file *file, struct cifs_tcon *tcon,
 			(char *)&fsctl_buf,
 			sizeof(struct file_zero_data_information),
 			CIFSMaxBufSize, NULL, NULL);
-	free_xid(xid);
 	filemap_invalidate_unlock(inode->i_mapping);
+out:
+	inode_unlock(inode);
+	free_xid(xid);
 	return rc;
 }