Bug #75496 [NEW]: Session ID Collision happened few times

From: dmitry dot yeskin at gmail dot com Operating system: Amazon OS PHP version: 7.0.25 Package: Session related Bug Type: Bug Bug description:Session ID Collision happened few times Description: ------------ Hello! We have an e-commerce website written with Yii2 framework. We don't modify session ids ourself. We just use session_start(); So here is what happened: we have a good traffic like 12000 unique users in 3 hrs of mornings every day. And for last 2 weeks - we got a session id collision 2 times. I mean - 2 customers came to website exactly at the same second and got shared session id. In result, they were able to see content of each other in their cart, until they started removing that content and even made a checkout, and then complained that ordered wrong item. Here is data from nginx log: -------- [ec2-user@scw ~]$ grep -r "73.111.163.135\|73.19.225.170" log.log 73.111.163.135 - - [26/Oct/2017:18:43:52 -0600] "GET /postcard?r=26oct2017 HTTP/2.0" 200 73.19.225.170 - - [26/Oct/2017:18:43:52 -0600] "GET /postcard?r=26oct2017 HTTP/2.0" 200 73.111.163.135 - - [26/Oct/2017:18:47:09 -0600] "POST /postcard?r=26oct2017 HTTP/2.0" 30 73.111.163.135 - - [26/Oct/2017:18:47:09 -0600] "GET /postcard?r=26oct2017 HTTP/2.0" 200 73.111.163.135 - - [26/Oct/2017:18:47:12 -0600] "GET /cart HTTP/2.0" 200 73.111.163.135 - - [26/Oct/2017:18:47:42 -0600] "POST /cart HTTP/2.0" 200 73.111.163.135 - - [26/Oct/2017:18:48:48 -0600] "GET /cart/checkout/ HTTP/2.0" 200 73.19.225.170 - - [26/Oct/2017:18:50:39 -0600] "POST /postcard?r=26oct2017 HTTP/2.0" 302 73.19.225.170 - - [26/Oct/2017:18:50:39 -0600] "GET /postcard?r=26oct2017 HTTP/2.0" 200 73.19.225.170 - - [26/Oct/2017:18:50:46 -0600] "GET /cart HTTP/2.0" 200 73.19.225.170 - - [26/Oct/2017:18:51:00 -0600] "GET /cart/remove/1 HTTP/2.0" 302 73.19.225.170 - - [26/Oct/2017:18:51:00 -0600] "GET /cart HTTP/2.0" 200 73.111.163.135 - - [26/Oct/2017:18:51:09 -0600] "POST /cart/checkout/ HTTP/2.0" 302 73.111.163.135 - - [26/Oct/2017:18:51:09 -0600] "GET /cart/checkout/complete HTTP/2.0" 200 73.19.225.170 - - [26/Oct/2017:18:51:17 -0600] "GET /cart/checkout/ HTTP/2.0" 200 ------------ You may see that both customers came to website at the same moment to postcard page (then they clicked add to cart and proceeded to cart, and then one of users saw wrong item there and called /cart/remove/1, then another user completed checkout, but he bought a wrong item and then complained to us). For 2 weeks we got 2 similar cases. After the first case we changed a hash entropy php settings in php.ini so session_id is now 48 chars but it didn't help to prevent second case. We solved this issue by adding user_agent to session var on controller init: if (session_status() == PHP_SESSION_NONE) { session_start(); } if (!isset($_SESSION['user_agent']) || empty($_SESSION['user_agent']) || $_SESSION['user_agent'] === Yii::$app->request->getUserAgent()) { } else { session_regenerate_id(); unset($_SESSION['user_agent']); unset($_SESSION['cart']); } if (!isset($_SESSION['user_agent'])) { $_SESSION['user_agent'] = Yii::$app->request->getUserAgent(); } But still wondered why this happens? I read in github php source code that php must use IP address and random value for session_id generation so it must be unique and i also read that php has some mechanisms to prevent session_id collisions. But looks like it doesn't work correctly. Again - everything great for thousands users. It only happened twice for last 2 weeks. We dont modify session_id value ourself. We just use session_start and work with $_SESSION variables after that. What are we doing wrong? Is it a bug? We have PHP 7.0.21 working as php-fpm and nginx PS. Doing PHP coding for 20 years, and see this for the first time. Test script: --------------- /** * Process adding line-item to cart * * @return boolean the status of addition */ public function addToCart() { if (session_status() == PHP_SESSION_NONE) { session_start(); } if (!isset($_SESSION['cart'])) { //$_SESSION['cart'] = array('items' => array(), 'coupon' => array(), 'subtotal' => '', 'discount' => '', 'shipping' => '', 'total' => ''); $_SESSION['cart'] = array('items' => array(), 'coupon' => array(), 'cost' => '', 'discount' => '', 'shipping' => '', 'total' => ''); } $cost = ($this->price + 1 - 1); // Converting string to number if (is_array($this->addons) && count($this->addons)>0) { foreach ($this->addons as $addon) { if (isset($addon['price']) && is_numeric($addon['price']) && !empty($addon['price'] + 1 - 1)) $cost += $addon['price']; } } $shippingCost = 0; if ($this->type == 'package' || $this->type == 'postcard' || $this->type == 'book') { $data = $this->data; if (isset($data['shipping']) && !empty($data['shipping']) && isset($data[$data['shipping']]) && is_numeric($data[$data['shipping']]) && !empty($data[$data['shipping']] + 1 - 1)) $shippingCost = $data[$data['shipping']]; } $_SESSION['cart']['items'][] = array( 'id' => $this->id, 'product_id' => $this->product_id, 'sku' => $this->sku, 'title' => $this->title, 'type' => $this->type, 'description' => $this->description, 'price' => number_format((float)$this->price, 2, '.', ''), 'picture' => $this->picture, 'data' => $this->data, 'address' => $this->address, 'addons' => $this->addons, 'cost' => number_format((float)$cost, 2, '.', ''), 'shipping' => number_format((float)$shippingCost, 2, '.', ''), 'subtotal' => number_format((float)($cost + $shippingCost), 2, '.', ''), 'draft' => $this->draft, ); $cost = 0; $shipping = 0; foreach ($_SESSION['cart']['items'] as $key => $item) { $cost += $item['cost']; $shipping += $item['shipping']; } $discount = (isset($_SESSION['cart']['discount']) && !empty($_SESSION['cart']['discount'])) ? $_SESSION['cart']['discount'] : 0; $_SESSION['cart']['cost'] = number_format((float)$cost, 2, '.', ''); $_SESSION['cart']['shipping'] = number_format((float)$shipping, 2, '.', ''); $_SESSION['cart']['total'] = number_format((float)($cost + $shipping - $discount), 2, '.', ''); return true; } -- Edit bug report at https://bugs.php.net/bug.php?id=75496&edit=1 -- Try a snapshot (PHP 5.4): https://bugs.php.net/fix.php?id=75496&r=trysnapshot54 Try a snapshot (PHP 5.5): https://bugs.php.net/fix.php?id=75496&r=trysnapshot55 Try a snapshot (trunk): https://bugs.php.net/fix.php?id=75496&r=trysnapshottrunk Fixed in SVN: https://bugs.php.net/fix.php?id=75496&r=fixed Fixed in release: https://bugs.php.net/fix.php?id=75496&r=alreadyfixed Need backtrace: https://bugs.php.net/fix.php?id=75496&r=needtrace Need Reproduce Script: https://bugs.php.net/fix.php?id=75496&r=needscript Try newer version: https://bugs.php.net/fix.php?id=75496&r=oldversion Not developer issue: https://bugs.php.net/fix.php?id=75496&r=support Expected behavior: https://bugs.php.net/fix.php?id=75496&r=notwrong Not enough info: https://bugs.php.net/fix.php?id=75496&r=notenoughinfo Submitted twice: https://bugs.php.net/fix.php?id=75496&r=submittedtwice register_globals: https://bugs.php.net/fix.php?id=75496&r=globals PHP 4 support discontinued: https://bugs.php.net/fix.php?id=75496&r=php4 Daylight Savings: https://bugs.php.net/fix.php?id=75496&r=dst IIS Stability: https://bugs.php.net/fix.php?id=75496&r=isapi Install GNU Sed: https://bugs.php.net/fix.php?id=75496&r=gnused Floating point limitations: https://bugs.php.net/fix.php?id=75496&r=float No Zend Extensions: https://bugs.php.net/fix.php?id=75496&r=nozend MySQL Configuration Error: https://bugs.php.net/fix.php?id=75496&r=mysqlcfg