Check if the contents of comment and reply are valid before persistence (#7677)

#### What type of PR is this?

/kind improvement
/area core
/milestone 2.21.x

#### What this PR does / why we need it:

This PR checks if the contents of comment and reply are valid before persistence to prevent users from XSS attacks.

#### Which issue(s) this PR fixes:

Fixes https://github.com/halo-dev/halo/issues/7675

#### Special notes for your reviewer:

Try to comment or reply with the contents from <https://cheatsheetseries.owasp.org/cheatsheets/XSS_Filter_Evasion_Cheat_Sheet.html>.

#### Does this PR introduce a user-facing change?

```release-note
检测评论和回复内容是否合法以防止 XSS 攻击
```

application/src/main/java/run/halo/app/content/comment/AbstractCommentService.java

@@ -2,6 +2,9 @@ package run.halo.app.content.comment;
 
 import java.util.Set;
 import lombok.RequiredArgsConstructor;
+import org.jsoup.Jsoup;
+import org.jsoup.safety.Safelist;
+import org.springframework.lang.NonNull;
 import org.springframework.security.core.context.ReactiveSecurityContextHolder;
 import org.springframework.util.Assert;
 import reactor.core.publisher.Mono;
@@ -21,6 +24,7 @@ public abstract class AbstractCommentService {
     protected final ReactiveExtensionClient client;
     protected final UserService userService;
     protected final CounterService counterService;
+    private final Safelist safelist = Safelist.relaxed();
 
     protected Mono<User> fetchCurrentUser() {
         return ReactiveSecurityContextHolder.getContext()
@@ -74,4 +78,14 @@ public abstract class AbstractCommentService {
             )
             .switchIfEmpty(Mono.fromSupplier(CommentStats::empty));
     }
+
+    /**
+     * Check if the given html is a safe HTML.
+     *
+     * @param html html content
+     * @return true if the html is safe, false otherwise
+     */
+    protected boolean isSafeHtml(@NonNull String html) {
+        return Jsoup.isValid(html, safelist);
+    }
 }

application/src/main/java/run/halo/app/content/comment/CommentServiceImpl.java

@@ -13,6 +13,7 @@ import org.springframework.data.domain.Sort;
 import org.springframework.lang.NonNull;
 import org.springframework.stereotype.Component;
 import org.springframework.util.Assert;
+import org.springframework.web.server.ServerWebInputException;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 import reactor.util.retry.Retry;
@@ -68,6 +69,13 @@ public class CommentServiceImpl extends AbstractCommentService implements Commen
 
     @Override
     public Mono<Comment> create(Comment comment) {
+        if (comment.getSpec() == null
+            || comment.getSpec().getContent() == null
+            || !isSafeHtml(comment.getSpec().getContent())) {
+            return Mono.error(new ServerWebInputException("""
+                The content of comment must not be empty or contains unsafe HTML.\
+                """));
+        }
         return environmentFetcher.fetchComment()
             .flatMap(commentSetting -> {
                 if (Boolean.FALSE.equals(commentSetting.getEnable())) {

application/src/main/java/run/halo/app/content/comment/ReplyServiceImpl.java

@@ -17,6 +17,7 @@ import org.springframework.dao.OptimisticLockingFailureException;
 import org.springframework.data.domain.Sort;
 import org.springframework.stereotype.Service;
 import org.springframework.util.Assert;
+import org.springframework.web.server.ServerWebInputException;
 import reactor.core.publisher.Flux;
 import reactor.core.publisher.Mono;
 import reactor.util.retry.Retry;
@@ -52,6 +53,13 @@ public class ReplyServiceImpl extends AbstractCommentService implements ReplySer
 
     @Override
     public Mono<Reply> create(String commentName, Reply reply) {
+        if (reply.getSpec() == null
+            || reply.getSpec().getContent() == null
+            || !isSafeHtml(reply.getSpec().getContent())) {
+            return Mono.error(new ServerWebInputException("""
+                The content of reply must not be empty or contains unsafe HTML.\
+                """));
+        }
         return client.get(Comment.class, commentName)
             .flatMap(this::approveComment)
             .filter(comment -> isTrue(comment.getSpec().getApproved()))