Stories by: Jonathan Corbet

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    Kernel space: The Tru64 Advanced Filesystem 02/07/2008 10:15:31

    On June 23, HP announced that it was releasing the source for the "Tru64 Advanced Filesystem" (or AdvFS) under version 2 of the GPL. This is, clearly, a large release of code from HP. What is a bit less clear is what the value of this release will be for Linux. In the end, that value is likely to be significant, but it will be probably realized in relatively indirect and difficult-to-measure ways.
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    Kernel space: Details of the vmsplice() exploit 19/03/2008 10:43:28

    Last week, we published a discussion of the vmsplice() exploit which showed how the failure to check permissions for a read operation led to a buffer overflow within the kernel. Subsequently, a linux-kernel reader pointed out that the article stopped short of a complete explanation: this is not an ordinary buffer overflow exploit. This article picks up where the last one left off and describes how the vmsplice() exploit makes use of this buffer overflow to take over the system. When vmsplice() is being used to feed data from memory into a pipe, the function charged with making it all happen is vmsplice_to_pipe(), found in fs/splice.c. It declares a couple of arrays of interest:
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    Kernel space: How to use a terabyte of RAM 19/03/2008 11:15:26

    We have not yet reached a point where systems - even high-end boxes - come with a terabyte of installed memory. But products like those from Violin Memory make it clear that the day is coming; one can buy a Violin box with 500GB in it now. So it seems worth asking the question: once one has spent the not inconsiderable sum to buy a box like that, what does one do with all that memory - especially now that the Firefox developers have gotten serious about fixing memory leaks?
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    Kernel space: the vmsplice() exploit 12/03/2008 11:15:39

    When this was being written, distributors were working quickly to ship kernel updates fixing the local root vulnerabilities in the vmsplice() system call. Unlike a number of other recent vulnerabilities which have required special situations (such as the presence of specific hardware) to exploit, these vulnerabilities are trivially exploited and the code to do so is circulating on the net. The author found himself wondering how such a wide hole could find its way into the core kernel code, so he set himself the task of figuring out just what was going on - a task which took rather longer than he had expected.
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    In search of a quality kernel 23/11/2007 09:51:13

    Discussions of kernel quality are not a new phenomenon on linux-kernel. It is, indeed, a topic which comes up with a certain regularity, more so than with many other free software projects. The size of the kernel, the rate at which its code changes, and the wide range of environments in which the kernel runs all lead to unique challenges; add in the fact that kernel bugs can lead to catastrophic system failures and you have the material for no end of debate.
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    Fair user scheduling for Linux 25/10/2007 10:24:45

    The Completely Fair Scheduler (CFS) was merged for the 2.6.23 kernel. One CFS feature which did not get in, though, was the group scheduling facility. Group scheduling makes the CFS fairness algorithm operate in a hierarchical fashion: processes are divided into groups, and, within each group, processes are scheduled fairly against one another. At the higher level, each group as a whole is given a fair share of the processor. The grouping of processes is done in user space in a highly flexible manner; the control groups (formerly "process containers") mechanism allows a management daemon to classify processes according to almost any policy.
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    Linux gets CAN support 18/10/2007 09:31:23

    The Controller Area Network (CAN) specification describes a networking stack aimed at a specific environment: embedded, realtime controller networks. At the physical layer, it uses a differential serial technology which is intended to be highly resistant to electrical noise. The higher-level protocols use short datagrams (eight bytes maximum payload) and extensive checksumming to minimize the effect of errors. The protocols are simple in the extreme, placing the smallest possible demand on embedded controllers. CAN will be found in relatively small and hostile environments -- inside automobiles, for example. So it makes sense that an automobile manufacturer--not the sort of company known for leading-edge Linux kernel development--is working to get a CAN implementation into the mainline kernel.
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    A generic tracing API for Linux 03/10/2007 10:00:14

    Dynamic kernel tracing remains high on the wishlists presented by many Linux users. While much work has been done to create a powerful tracing capability, very little of that work has found its way into the mainline. The recent posting of one small piece of infrastructure may help to change that situation, though.
 
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