Messages in this thread |  | | From | Zefram <> | Subject | Re: Misc Fixes | Date | Tue, 9 Jul 1996 17:23:13 +0100 (BST) |
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>Tried getting this patch through during 1.3; Linus rejected it as making >it too easy for module to circumvent securelevel. The fix he wanted was >write a functional interfaces so that it would be possible for ext2 to >obtain the current securelevel settings, without being able to set it.
Unless I'm gravely mistaken about the nature of Linux modules, any loaded module can *actually* modify securelevel -- or indeed do anything that the current securelevel would normally prohibit -- regardless of this patch. The only difference is that without this patch (a) a lot of things are not easily modularised and (b) it's non-trivial to write a module to maliciously change the securelevel (though still easy to do other nasty things).
A function such as you describe will effectively give away the address of securelevel to malicious code (it knows where the function is and doesn't need to do as much as a disassembly), but will still hinder legitimate code. The obvious solution is to disallow loading/unloading of modules at a sufficiently high securelevel.
-zefram
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