cifs: revalidate mapping prior to satisfying read_iter request with cache=loose

Before satisfying a read with cache=loose, we should always check
that the pagecache is valid before allowing a read to be satisfied
out of it.
Reported-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Signed-off-by: Jeff Layton <jlayton@poochiereds.net>
Signed-off-by: Steve French <smfrench@gmail.com>

fs/cifs/cifsfs.c

@@ -725,6 +725,19 @@ cifs_do_mount(struct file_system_type *fs_type,
 	goto out;
 }
 
+static ssize_t
+cifs_loose_read_iter(struct kiocb *iocb, struct iov_iter *iter)
+{
+	ssize_t rc;
+	struct inode *inode = file_inode(iocb->ki_filp);
+
+	rc = cifs_revalidate_mapping(inode);
+	if (rc)
+		return rc;
+
+	return generic_file_read_iter(iocb, iter);
+}
+
 static ssize_t cifs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 {
 	struct inode *inode = file_inode(iocb->ki_filp);
@@ -881,7 +894,7 @@ const struct inode_operations cifs_symlink_inode_ops = {
 const struct file_operations cifs_file_ops = {
 	.read = new_sync_read,
 	.write = new_sync_write,
-	.read_iter = generic_file_read_iter,
+	.read_iter = cifs_loose_read_iter,
 	.write_iter = cifs_file_write_iter,
 	.open = cifs_open,
 	.release = cifs_close,
@@ -939,7 +952,7 @@ const struct file_operations cifs_file_direct_ops = {
 const struct file_operations cifs_file_nobrl_ops = {
 	.read = new_sync_read,
 	.write = new_sync_write,
-	.read_iter = generic_file_read_iter,
+	.read_iter = cifs_loose_read_iter,
 	.write_iter = cifs_file_write_iter,
 	.open = cifs_open,
 	.release = cifs_close,