fs: dlm: add debugfs rawmsg send functionality

This patch adds a dlm functionality to send a raw dlm message to a
specific cluster node. This raw message can be build by user space and
send out by writing the message to "rawmsg" dlm debugfs file.

There is a in progress scapy dlm module which provides a easy build of
DLM messages in user space. For example:

DLM(h_cmd=3, o_nextcmd=1, h_nodeid=1, h_lockspace=0xe4f48a18, ...)

The goal is to provide an easy reproducable state to crash DLM or to
fuzz the DLM kernel stack if there are possible ways to crash it.

Note: that if the sequence number is zero and dlm version is not set to
3.1 the kernel will automatic will set a right sequence number, otherwise
DLM stack testing is not possible.
Signed-off-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>

fs/dlm/debug_fs.c

@@ -768,6 +768,42 @@ static int dlm_version_show(struct seq_file *file, void *offset)
 }
 DEFINE_SHOW_ATTRIBUTE(dlm_version);
 
+static ssize_t dlm_rawmsg_write(struct file *fp, const char __user *user_buf,
+				size_t count, loff_t *ppos)
+{
+	void *buf;
+	int ret;
+
+	if (count > PAGE_SIZE || count < sizeof(struct dlm_header))
+		return -EINVAL;
+
+	buf = kmalloc(PAGE_SIZE, GFP_NOFS);
+	if (!buf)
+		return -ENOMEM;
+
+	if (copy_from_user(buf, user_buf, count)) {
+		ret = -EFAULT;
+		goto out;
+	}
+
+	ret = dlm_midcomms_rawmsg_send(fp->private_data, buf, count);
+	if (ret)
+		goto out;
+
+	kfree(buf);
+	return count;
+
+out:
+	kfree(buf);
+	return ret;
+}
+
+static const struct file_operations dlm_rawmsg_fops = {
+	.open	= simple_open,
+	.write	= dlm_rawmsg_write,
+	.llseek	= no_llseek,
+};
+
 void *dlm_create_debug_comms_file(int nodeid, void *data)
 {
 	struct dentry *d_node;
@@ -782,6 +818,7 @@ void *dlm_create_debug_comms_file(int nodeid, void *data)
 	debugfs_create_file("send_queue_count", 0444, d_node, data,
 			    &dlm_send_queue_cnt_fops);
 	debugfs_create_file("version", 0444, d_node, data, &dlm_version_fops);
+	debugfs_create_file("rawmsg", 0200, d_node, data, &dlm_rawmsg_fops);
 
 	return d_node;
 }

fs/dlm/midcomms.c

@@ -1427,3 +1427,51 @@ int dlm_midcomms_close(int nodeid)
 
 	return ret;
 }
+
+/* debug functionality to send raw dlm msg from user space */
+struct dlm_rawmsg_data {
+	struct midcomms_node *node;
+	void *buf;
+};
+
+static void midcomms_new_rawmsg_cb(void *data)
+{
+	struct dlm_rawmsg_data *rd = data;
+	struct dlm_header *h = rd->buf;
+
+	switch (h->h_version) {
+	case cpu_to_le32(DLM_VERSION_3_1):
+		break;
+	default:
+		switch (h->h_cmd) {
+		case DLM_OPTS:
+			if (!h->u.h_seq)
+				h->u.h_seq = rd->node->seq_send++;
+			break;
+		default:
+			break;
+		}
+		break;
+	}
+}
+
+int dlm_midcomms_rawmsg_send(struct midcomms_node *node, void *buf,
+			     int buflen)
+{
+	struct dlm_rawmsg_data rd;
+	struct dlm_msg *msg;
+	char *msgbuf;
+
+	rd.node = node;
+	rd.buf = buf;
+
+	msg = dlm_lowcomms_new_msg(node->nodeid, buflen, GFP_NOFS,
+				   &msgbuf, midcomms_new_rawmsg_cb, &rd);
+	if (!msg)
+		return -ENOMEM;
+
+	memcpy(msgbuf, buf, buflen);
+	dlm_lowcomms_commit_msg(msg);
+	return 0;
+}
+

fs/dlm/midcomms.h

@@ -28,6 +28,8 @@ const char *dlm_midcomms_state(struct midcomms_node *node);
 unsigned long dlm_midcomms_flags(struct midcomms_node *node);
 int dlm_midcomms_send_queue_cnt(struct midcomms_node *node);
 uint32_t dlm_midcomms_version(struct midcomms_node *node);
+int dlm_midcomms_rawmsg_send(struct midcomms_node *node, void *buf,
+			     int buflen);
 
 #endif				/* __MIDCOMMS_DOT_H__ */