Add markdown_escape setting

This setting allows to escape HTML in markdown rendering or not.
The goal behind it is to avoid XSS issue in shared instances.

More info:

  * the setting is set to true by default
  * it is set to false for anyone who already have the plugin enabled
  (avoid breaking existing entries)
  * improve the HTML sanitization when the setting is set to false - but don't consider it XSS proof
  * mention the setting in the plugin README

plugins/markdown/README.md

@@ -50,9 +50,20 @@ If the tag `nomarkdown` is set for a shaare, it won't be converted to Markdown s
  
 > Note: this is a special tag, so it won't be displayed in link list.
 
-### HTML rendering
+### HTML escape
 
-Markdown support HTML tags. For example:
+By default, HTML tags are escaped. You can enable HTML tags rendering
+by setting `security.markdwon_escape` to `false` in `data/config.json.php`:
+
+```json
+{
+  "security": {
+    "markdown_escape": false
+  }
+}
+```
+
+With this setting, Markdown support HTML tags. For example:
 
     > <strong>strong</strong><strike>strike</strike>
    
@@ -60,12 +71,14 @@ Will render as:
 
 > <strong>strong</strong><strike>strike</strike>
 
-If you want to shaare HTML code, it is necessary to use inline code or code blocks.
-  
-**If your shaared descriptions containing HTML tags before enabling the markdown plugin, 
-enabling it might break your page.**
 
-> Note: HTML tags such as script, iframe, etc. are disabled for security reasons.
+**Warning:**
+
+  * This setting might present **security risks** (XSS) on shared instances, even though tags 
+  such as script, iframe, etc should be disabled.
+  * If you want to shaare HTML code, it is necessary to use inline code or code blocks.
+  * If your shaared descriptions contained HTML tags before enabling the markdown plugin, 
+enabling it might break your page.
 
 ### Known issue
 

plugins/markdown/markdown.php

@@ -14,18 +14,19 @@ define('NO_MD_TAG', 'nomarkdown');
 /**
  * Parse linklist descriptions.
  *
- * @param array $data linklist data.
+ * @param array         $data linklist data.
+ * @param ConfigManager $conf instance.
  *
  * @return mixed linklist data parsed in markdown (and converted to HTML).
  */
-function hook_markdown_render_linklist($data)
+function hook_markdown_render_linklist($data, $conf)
 {
     foreach ($data['links'] as &$value) {
         if (!empty($value['tags']) && noMarkdownTag($value['tags'])) {
             $value = stripNoMarkdownTag($value);
             continue;
         }
-        $value['description'] = process_markdown($value['description']);
+        $value['description'] = process_markdown($value['description'], $conf->get('security.markdown_escape', true));
     }
     return $data;
 }
@@ -34,17 +35,18 @@ function hook_markdown_render_linklist($data)
  * Parse feed linklist descriptions.
  *
  * @param array $data linklist data.
+ * @param ConfigManager $conf instance.
  *
  * @return mixed linklist data parsed in markdown (and converted to HTML).
  */
-function hook_markdown_render_feed($data)
+function hook_markdown_render_feed($data, $conf)
 {
     foreach ($data['links'] as &$value) {
         if (!empty($value['tags']) && noMarkdownTag($value['tags'])) {
             $value = stripNoMarkdownTag($value);
             continue;
         }
-        $value['description'] = process_markdown($value['description']);
+        $value['description'] = process_markdown($value['description'], $conf->get('security.markdown_escape', true));
     }
 
     return $data;
@@ -53,11 +55,12 @@ function hook_markdown_render_feed($data)
 /**
  * Parse daily descriptions.
  *
- * @param array $data daily data.
+ * @param array         $data daily data.
+ * @param ConfigManager $conf instance.
  *
  * @return mixed daily data parsed in markdown (and converted to HTML).
  */
-function hook_markdown_render_daily($data)
+function hook_markdown_render_daily($data, $conf)
 {
     // Manipulate columns data
     foreach ($data['cols'] as &$value) {
@@ -66,7 +69,10 @@ function hook_markdown_render_daily($data)
                 $value2 = stripNoMarkdownTag($value2);
                 continue;
             }
-            $value2['formatedDescription'] = process_markdown($value2['formatedDescription']);
+            $value2['formatedDescription'] = process_markdown(
+                $value2['formatedDescription'],
+                $conf->get('security.markdown_escape', true)
+            );
         }
     }
 
@@ -250,7 +256,7 @@ function sanitize_html($description)
             $description);
     }
     $description = preg_replace(
-        '#(<[^>]+)on[a-z]*="[^"]*"#is',
+        '#(<[^>]+)on[a-z]*="?[^ "]*"?#is',
         '$1',
         $description);
     return $description;
@@ -265,10 +271,11 @@ function sanitize_html($description)
  *   5. Wrap description in 'markdown' CSS class.
  *
  * @param string $description input description text.
+ * @param bool   $escape      escape HTML entities
  *
  * @return string HTML processed $description.
  */
-function process_markdown($description)
+function process_markdown($description, $escape = true)
 {
     $parsedown = new Parsedown();
 
@@ -278,7 +285,7 @@ function process_markdown($description)
     $processedDescription = reverse_text2clickable($processedDescription);
     $processedDescription = unescape($processedDescription);
     $processedDescription = $parsedown
-        ->setMarkupEscaped(false)
+        ->setMarkupEscaped($escape)
         ->setBreaksEnabled(true)
         ->text($processedDescription);
     $processedDescription = sanitize_html($processedDescription);