Author Archives: admin

The Microsoft C++ Compiler Turns 20!

Posted on February 9, 2012 by admin

This month, we enter the third decade of C++ at Microsoft. It was twenty years ago, in February of 1992, that we released our first C++ compiler: Microsoft C/C++ 7.0. Before then, we already worked with several of the C++ … Continue reading →

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fcgi vs. gunicorn vs. uWSGI

Posted on February 6, 2012 by admin

uwsgi is the latest and greatest WSGI server and promising to be the fastest possible way to run Nginx + Django. Proof here But! Is it that simple? Especially if you’re involving Django herself. So I set out to benchmark … Continue reading →

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Critical PHP Remote Vulnerability Introduced in Fix for PHP Hashtable Collision DOS

Posted on February 3, 2012 by admin

Today, Stefan Esser (@i0n1c) reported a critical remotely exploitable vulnerability in PHP 5.3.9 (updateassigned CVE-2012-0830). The funny thing is that this vulnerability was introduced in the fix for the hash collision DOS (CVE-2011-4885) reported in December. The Vulnerable Fix The fix to … Continue reading →

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Understanding Linux CPU Load – when should you be worried?

Posted on February 3, 2012 by admin

You might be familiar with Linux load averages already. Load averages are the three numbers shown with the uptime and top commands – they look like this: load average: 0.09, 0.05, 0.01 Most people have an inkling of what the load averages mean: the … Continue reading →

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Linux Local Privilege Escalation via SUID /proc/pid/mem Write

Posted on January 30, 2012 by admin

Introducing Mempodipper, an exploit for CVE-2012-0056. /proc/pid/mem is an interface for reading and writing, directly, process memory by seeking around with the same addresses as the process’s virtual memory space. In 2.6.39, the protections against unauthorized access to /proc/pid/mem were … Continue reading →

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EXT4 vs XFS: large volumes with low-end RAID controller

Posted on January 12, 2012 by admin

Some months ago, I wrote an article comparing EXT3, EXT4, XFS and BTRFS filesystem performances with a Fedora 14 x86_64 installation done on a Dell Latitude D620 laptop. While the results were quite interesting (especially to evaluate BTRFS performance), they … Continue reading →

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alloc_sem of Ext4 block group

Posted on January 10, 2012 by admin

Yesterday Amir Goldstein sent me an email for a deadlock issue. I was in Chinese New Year vacation, could not have time to check the code (also I know I can not answer his question with ease). Thanks to Ted, … Continue reading →

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Three Practical System Workloads of Taobao

Posted on January 10, 2012 by admin

Days ago, I gave a talk on an academic seminar at ACT of Beihang University (http://act.buaa.edu.cn/). In my talk, I introduced three typical system workloads we (a group of system software developers inside Taobao) observed from the most heavily used/deployed … Continue reading →

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Don’t waste your SSD blocks

Posted on January 10, 2012 by admin

These days, one of my colleagues asked me a question, he formatted an ~80G Ext3 file system on SSD. After mounted the file system, the df output was, Filesystem 1K-blocks Used Available Use% Mounted on /dev/sdb1 77418272 184216 73301344 1 … Continue reading →

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Random I/O — Is raw device always faster than file system ?

Posted on January 10, 2012 by admin

For some implementations of distributed file systems, like TFS [1], developers think storing data on raw device directly (e.g. /dev/sdb, /dev/sdc…) might be faster than on file systems. Their choice is reasonable, 1, Random I/O on large file cannot get … Continue reading →

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