13.9. Guarding Against Resource Starvation Attacks on Unix


You need to prevent resource starvation attacks against your application.


The operating system does not trust the applications that it allows to run. For this reason, the operating system imposes limits on certain resources. The limitations are imposed to prevent an application from using up all of the available system resources, thus denying other running applications the ability to run. The default limits are usually set much higher than they need to be, which ends up allowing any given application to use up far more resources than it ordinarily should.

Unix provides a mechanism by which an application can self-impose restrictive limits on the resources that it uses. It’s a good idea for the programmer to lower the limits to a point where the application can run comfortably, but if something unexpected happens (such as a memory leak or, more to the point, a denial of service attack), the limits cause the application to begin failing without bringing down the rest of the system with it.


Operating system resources are difficult for an application to control; the pooling approach used in threads and sockets is difficult to implement when the application does not explicitly allocate and destroy its own resources. System resources such as memory, CPU time, disk space, and open file descriptors are best managed using system quotas. The programmer can never be sure that system quotas are enabled when ...

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