Monday, May 04, 2009

Cooperative multitasking and security, a browser perspective

An article over on Ars Technica goes into some detail about a dispute between two Firefox extensions that has gotten nasty. It seems that the extension environment inside Firefox (and that other Mozilla browser, SeaMonkey) is not sandboxed to any significant degree. The developer of NoScript was able to write in a complete disabling of the AdBlock Pro extension.

In some ways this reminds me strongly of how NetWare works. NetWare uses cooperative multitasking, rather than the preemptive multitasking used is pretty much every other modern server-class OS. This is part of the reason NetWare can squeeze out the performance it does under high load. The Firefox extensions run as children of the main Firefox process, can freely interact with each other, and when they crash hard can take the whole environment down with it.

Another way it reminds me of NetWare is the seeming lack of memory protection. In NetWare, unless you specifically declare that a module is to run in a protected memory space, it runs in the Kernel's memory space. This means that one program can access the memory of another program, so long as they're in the same memory space. This stands in contrast to other operating systems which provide a protected memory space for each process. It sounds to me like Firefox has a single memory space equivalent, and all process have access to it. This allows the extension-war described above to be possible without resorting to outright hacking around security features.

Moving away from a cooperative multitasking model made Windows at lot more stable (Win3.11 to Win95) as did the introduction of true memory protection (Win98 to Win2K). Memory protection is a major security barrier, and is something that Firefox seems to lack. If a Firefox install is unlucky enough to have an evil extension added to it, all the data that passes through that browser could be copied to persons nefarious, much like the Browser Helper Objects in IE.

Does it seem odd to you that I'm talking about Operating System protection features being built into browsers? These days browsers are in large part operating systems on their own, albeit ones missing the key feature of having exclusive control of the hardware.

These problems to appear to be on the verge of changing. Both Chrome and IE8 launch each browser tab in its own process, which adds a barrier between processes spawned in those tabs. That way when a flash game starts consuming all available CPU, you can kill the tab and keep the rest of your browser session running. Unfortunately, process separation still won't stop NoScript from killing AdBlocker. For that, more work needs to be done.

Labels: ,

Comments: Post a Comment

<< Home

This page is powered by Blogger. Isn't yours?