1 files changed, 235 insertions, 0 deletions
diff --git a/modules/markup/sanitizer.go b/modules/markup/sanitizer.go
new file mode 100644
index 00000000..d07bba30
--- /dev/null
+++ b/modules/markup/sanitizer.go
@@ -0,0 +1,235 @@
+// Copyright 2017 The Gitea Authors. All rights reserved.
+// Copyright 2017 The Gogs Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+package markup
+
+import (
+	"io"
+	"net/url"
+	"regexp"
+	"sync"
+
+	"code.gitea.io/gitea/modules/setting"
+
+	"github.com/microcosm-cc/bluemonday"
+)
+
+// Sanitizer is a protection wrapper of *bluemonday.Policy which does not allow
+// any modification to the underlying policies once it's been created.
+type Sanitizer struct {
+	defaultPolicy     *bluemonday.Policy
+	descriptionPolicy *bluemonday.Policy
+	rendererPolicies  map[string]*bluemonday.Policy
+	init              sync.Once
+}
+
+var (
+	sanitizer     = &Sanitizer{}
+	allowAllRegex = regexp.MustCompile(".+")
+)
+
+// NewSanitizer initializes sanitizer with allowed attributes based on settings.
+// Multiple calls to this function will only create one instance of Sanitizer during
+// entire application lifecycle.
+func NewSanitizer() {
+	sanitizer.init.Do(func() {
+		InitializeSanitizer()
+	})
+}
+
+// InitializeSanitizer (re)initializes the current sanitizer to account for changes in settings
+func InitializeSanitizer() {
+	sanitizer.rendererPolicies = map[string]*bluemonday.Policy{}
+	sanitizer.defaultPolicy = createDefaultPolicy()
+	sanitizer.descriptionPolicy = createRepoDescriptionPolicy()
+
+	for name, renderer := range renderers {
+		sanitizerRules := renderer.SanitizerRules()
+		if len(sanitizerRules) > 0 {
+			policy := createDefaultPolicy()
+			addSanitizerRules(policy, sanitizerRules)
+			sanitizer.rendererPolicies[name] = policy
+		}
+	}
+}
+
+func createDefaultPolicy() *bluemonday.Policy {
+	policy := bluemonday.UGCPolicy()
+
+	// For JS code copy and Mermaid loading state
+	policy.AllowAttrs("class").Matching(regexp.MustCompile(`^code-block( is-loading)?$`)).OnElements("pre")
+
+	// For color preview
+	policy.AllowAttrs("class").Matching(regexp.MustCompile(`^color-preview$`)).OnElements("span")
+
+	// For attention
+	policy.AllowAttrs("class").Matching(regexp.MustCompile(`^attention-title$`)).OnElements("p")
+	policy.AllowAttrs("class").Matching(regexp.MustCompile(`^attention-header attention-\w+$`)).OnElements("blockquote")
+	policy.AllowAttrs("class").Matching(regexp.MustCompile(`^attention-\w+$`)).OnElements("strong")
+	policy.AllowAttrs("class").Matching(regexp.MustCompile(`^attention-icon attention-\w+ svg octicon-[\w-]+$`)).OnElements("svg")
+	policy.AllowAttrs("viewBox", "width", "height", "aria-hidden").OnElements("svg")
+	policy.AllowAttrs("fill-rule", "d").OnElements("path")
+
+	// For Chroma markdown plugin
+	policy.AllowAttrs("class").Matching(regexp.MustCompile(`^(chroma )?language-[\w-]+( display)?( is-loading)?$`)).OnElements("code")
+
+	// Checkboxes
+	policy.AllowAttrs("type").Matching(regexp.MustCompile(`^checkbox$`)).OnElements("input")
+	policy.AllowAttrs("checked", "disabled", "data-source-position").OnElements("input")
+
+	// Custom URL-Schemes
+	if len(setting.Markdown.CustomURLSchemes) > 0 {
+		policy.AllowURLSchemes(setting.Markdown.CustomURLSchemes...)
+	} else {
+		policy.AllowURLSchemesMatching(allowAllRegex)
+
+		// Even if every scheme is allowed, these three are blocked for security reasons
+		disallowScheme := func(*url.URL) bool {
+			return false
+		}
+		policy.AllowURLSchemeWithCustomPolicy("javascript", disallowScheme)
+		policy.AllowURLSchemeWithCustomPolicy("vbscript", disallowScheme)
+		policy.AllowURLSchemeWithCustomPolicy("data", disallowScheme)
+	}
+
+	// Allow classes for anchors
+	policy.AllowAttrs("class").Matching(regexp.MustCompile(`ref-issue( ref-external-issue)?`)).OnElements("a")
+
+	// Allow classes for task lists
+	policy.AllowAttrs("class").Matching(regexp.MustCompile(`task-list-item`)).OnElements("li")
+
+	// Allow classes for org mode list item status.
+	policy.AllowAttrs("class").Matching(regexp.MustCompile(`^(unchecked|checked|indeterminate)$`)).OnElements("li")
+
+	// Allow icons
+	policy.AllowAttrs("class").Matching(regexp.MustCompile(`^icon(\s+[\p{L}\p{N}_-]+)+$`)).OnElements("i")
+
+	// Allow classes for emojis
+	policy.AllowAttrs("class").Matching(regexp.MustCompile(`emoji`)).OnElements("img")
+
+	// Allow icons, emojis, chroma syntax and keyword markup on span
+	policy.AllowAttrs("class").Matching(regexp.MustCompile(`^((icon(\s+[\p{L}\p{N}_-]+)+)|(emoji)|(language-math display)|(language-math inline))$|^([a-z][a-z0-9]{0,2})$|^` + keywordClass + `$`)).OnElements("span")
+
+	// Allow 'color' and 'background-color' properties for the style attribute on text elements.
+	policy.AllowStyles("color", "background-color").OnElements("span", "p")
+
+	// Allow classes for file preview links...
+	policy.AllowAttrs("class").Matching(regexp.MustCompile("^(lines-num|lines-code chroma)$")).OnElements("td")
+	policy.AllowAttrs("class").Matching(regexp.MustCompile("^code-inner$")).OnElements("code")
+	policy.AllowAttrs("class").Matching(regexp.MustCompile("^file-preview-box$")).OnElements("div")
+	policy.AllowAttrs("class").Matching(regexp.MustCompile("^ui table$")).OnElements("div")
+	policy.AllowAttrs("class").Matching(regexp.MustCompile("^header$")).OnElements("div")
+	policy.AllowAttrs("data-line-number").Matching(regexp.MustCompile("^[0-9]+$")).OnElements("span")
+	policy.AllowAttrs("class").Matching(regexp.MustCompile("^text small grey$")).OnElements("span")
+	policy.AllowAttrs("class").Matching(regexp.MustCompile("^file-preview*")).OnElements("table")
+	policy.AllowAttrs("class").Matching(regexp.MustCompile("^lines-escape$")).OnElements("td")
+	policy.AllowAttrs("class").Matching(regexp.MustCompile("^toggle-escape-button btn interact-bg$")).OnElements("button")
+	policy.AllowAttrs("title").OnElements("button")
+	policy.AllowAttrs("class").Matching(regexp.MustCompile("^ambiguous-code-point$")).OnElements("span")
+	policy.AllowAttrs("data-tooltip-content").OnElements("span")
+	policy.AllowAttrs("class").Matching(regexp.MustCompile("muted|(text black)")).OnElements("a")
+	policy.AllowAttrs("class").Matching(regexp.MustCompile("^ui warning message tw-text-left$")).OnElements("div")
+
+	// Allow generally safe attributes
+	generalSafeAttrs := []string{
+		"abbr", "accept", "accept-charset",
+		"accesskey", "action", "align", "alt",
+		"aria-describedby", "aria-hidden", "aria-label", "aria-labelledby",
+		"axis", "border", "cellpadding", "cellspacing", "char",
+		"charoff", "charset", "checked",
+		"clear", "cols", "colspan", "color",
+		"compact", "coords", "datetime", "dir",
+		"disabled", "enctype", "for", "frame",
+		"headers", "height", "hreflang",
+		"hspace", "ismap", "label", "lang",
+		"maxlength", "media", "method",
+		"multiple", "name", "nohref", "noshade",
+		"nowrap", "open", "prompt", "readonly", "rel", "rev",
+		"rows", "rowspan", "rules", "scope",
+		"selected", "shape", "size", "span",
+		"start", "summary", "tabindex", "target",
+		"title", "type", "usemap", "valign", "value",
+		"vspace", "width", "itemprop",
+	}
+
+	generalSafeElements := []string{
+		"h1", "h2", "h3", "h4", "h5", "h6", "h7", "h8", "br", "b", "i", "strong", "em", "a", "pre", "code", "img", "tt",
+		"div", "ins", "del", "sup", "sub", "p", "ol", "ul", "table", "thead", "tbody", "tfoot", "blockquote", "label",
+		"dl", "dt", "dd", "kbd", "q", "samp", "var", "hr", "ruby", "rt", "rp", "li", "tr", "td", "th", "s", "strike", "summary",
+		"details", "caption", "figure", "figcaption",
+		"abbr", "bdo", "cite", "dfn", "mark", "small", "span", "time", "video", "wbr",
+	}
+
+	policy.AllowAttrs(generalSafeAttrs...).OnElements(generalSafeElements...)
+
+	policy.AllowAttrs("src", "autoplay", "controls").OnElements("video")
+
+	policy.AllowAttrs("itemscope", "itemtype").OnElements("div")
+
+	// FIXME: Need to handle longdesc in img but there is no easy way to do it
+
+	// Custom keyword markup
+	addSanitizerRules(policy, setting.ExternalSanitizerRules)
+
+	return policy
+}
+
+// createRepoDescriptionPolicy returns a minimal more strict policy that is used for
+// repository descriptions.
+func createRepoDescriptionPolicy() *bluemonday.Policy {
+	policy := bluemonday.NewPolicy()
+	policy.AllowStandardURLs()
+
+	// Allow italics and bold.
+	policy.AllowElements("i", "b", "em", "strong")
+
+	// Allow code.
+	policy.AllowElements("code")
+
+	// Allow links
+	policy.AllowAttrs("href", "target", "rel").OnElements("a")
+
+	// Allow classes for emojis
+	policy.AllowAttrs("class").Matching(regexp.MustCompile(`^emoji$`)).OnElements("img", "span")
+	policy.AllowAttrs("aria-label").OnElements("span")
+
+	return policy
+}
+
+func addSanitizerRules(policy *bluemonday.Policy, rules []setting.MarkupSanitizerRule) {
+	for _, rule := range rules {
+		if rule.AllowDataURIImages {
+			policy.AllowDataURIImages()
+		}
+		if rule.Element != "" {
+			if rule.Regexp != nil {
+				policy.AllowAttrs(rule.AllowAttr).Matching(rule.Regexp).OnElements(rule.Element)
+			} else {
+				policy.AllowAttrs(rule.AllowAttr).OnElements(rule.Element)
+			}
+		}
+	}
+}
+
+// SanitizeDescription sanitizes the HTML generated for a repository description.
+func SanitizeDescription(s string) string {
+	NewSanitizer()
+	return sanitizer.descriptionPolicy.Sanitize(s)
+}
+
+// Sanitize takes a string that contains a HTML fragment or document and applies policy whitelist.
+func Sanitize(s string) string {
+	NewSanitizer()
+	return sanitizer.defaultPolicy.Sanitize(s)
+}
+
+// SanitizeReader sanitizes a Reader
+func SanitizeReader(r io.Reader, renderer string, w io.Writer) error {
+	NewSanitizer()
+	policy, exist := sanitizer.rendererPolicies[renderer]
+	if !exist {
+		policy = sanitizer.defaultPolicy
+	}
+	return policy.SanitizeReaderToWriter(r, w)
+}