diff --git a/back/main.py b/back/main.py
index d7db77e..c33b4ee 100644
--- a/back/main.py
+++ b/back/main.py
@@ -3,9 +3,11 @@
 from flask import Flask, jsonify, request, abort, send_from_directory
 from flask_cors import CORS
 from flask_sqlalchemy import SQLAlchemy
+from sqlalchemy.orm import foreign
 import os
 import uuid
 import json
+import imghdr
 from datetime import datetime
 
 app = Flask(__name__)
@@ -62,9 +64,10 @@ class Submission(db.Model):
     comments = db.relationship('Comment', backref='submission', lazy=True, cascade='all, delete-orphan')
     hashtags = db.relationship(
         'Hashtag',
-        primaryjoin="and_(Hashtag.type==0, Hashtag.target_id==Submission.id)",
+        primaryjoin="and_(Hashtag.type==0, foreign(Hashtag.target_id)==Submission.id)",
         cascade='all, delete-orphan',
-        lazy=True
+        lazy=True,
+        overlaps="hashtags"
     )
 
 class Comment(db.Model):
@@ -78,9 +81,10 @@ class Comment(db.Model):
     parent_comment_id = db.Column(db.Integer, db.ForeignKey('comments.id'), nullable=True)
     hashtags = db.relationship(
         'Hashtag',
-        primaryjoin="and_(Hashtag.type==1, Hashtag.target_id==Comment.id)",
+        primaryjoin="and_(Hashtag.type==1, foreign(Hashtag.target_id)==Comment.id)",
         cascade='all, delete-orphan',
-        lazy=True
+        lazy=True,
+        overlaps="hashtags"
     )
 
 class Report(db.Model):
@@ -207,7 +211,6 @@ def save_hashtags(tag_type, target_id, hashtopic):
             name=tag
         )
         db.session.add(new_tag)
-    db.session.commit()
     
 # --- 用户普通api端点 ---
 @app.route('/api/settings', methods=['GET'])
@@ -345,14 +348,16 @@ def submit_post():
             updated_at=now,
         )
         db.session.add(new_post)
-        db.session.commit()
+        db.session.flush()
         
         # 保存 Hashtags
         save_hashtags(0, new_post.id, hashtopic)
+        db.session.commit()
         
         code = 1002 if new_post.status == 'Pending' else 1001
         return jsonify({"code": code, "data": {"id": new_post.id}})
     except Exception as e:
+        db.session.rollback()
         return jsonify({"code": 2003, "data": f"投稿失败: {str(e)}"})
 
 @app.route('/api/comment', methods=['POST'])
@@ -398,13 +403,15 @@ def submit_comment():
             parent_comment_id=None if parent_comment_id == 0 else parent_comment_id
         )
         db.session.add(new_comment)
-        db.session.commit()
+        db.session.flush()
         
         # 保存 Hashtags
         save_hashtags(1, new_comment.id, hashtopic)
+        db.session.commit()
         
         return jsonify({"code": 1001, "data": {"id": new_comment.id}})
     except Exception as e:
+        db.session.rollback()
         return jsonify({"code": 2003, "data": f"评论失败: {str(e)}"})
 
 @app.route('/api/report', methods=['POST'])
@@ -498,6 +505,20 @@ def upload_pic():
         if not ext or (FILE_FORMATS and ext not in FILE_FORMATS):
             return jsonify({"code": 2007, "data": "上传的文件类型不支持"})
 
+        header = file.read(512)
+        file.seek(0)
+        detected = imghdr.what(None, header)
+        ext_map = {
+            'jpg': 'jpeg',
+            'jpeg': 'jpeg',
+            'png': 'png',
+            'gif': 'gif',
+            'webp': 'webp',
+        }
+        expected = ext_map.get(ext)
+        if not expected or detected != expected:
+            return jsonify({"code": 2007, "data": "上传的文件类型不支持"})
+
         filename = f"{uuid.uuid4().hex}.{ext}"
         filepath = os.path.join(IMG_DIR, filename)
         file.save(filepath)