Re: Over-riding symbols in the Kernel causes Kernel Panic

[Jesper Juhl <jesper.juhl@gmail.com>]

On 11/23/05, Grant Coady <grant_lkml@dodo.com.au> wrote:
> On Wed, 23 Nov 2005 19:04:41 +0100, Jesper Juhl <jesper.juhl@gmail.com> wrote:
>
> >On 11/23/05, Bill Davidsen <davidsen@tmr.com> wrote:
> >> Ashutosh Naik wrote:
> >> > Hi,
> >> >
> >> > I made e1000 ( or for that matter anything) a part of the 2.6.15-rc1
> >> > kernel and booted the kernel. Next I compiled e1000 as a module (
> >> > e1000.ko ), and tried to insmod it into the kernel( which already had
> >> > e1000 a compiled as a part of the kernel). I observed that
> >> > /proc/kallsyms contained two copies of all the symbols exported by
> >> > e1000, and I also got a Kernel Panic on the way.
> >> >
> >> > Is this behaviour natural and desirable ?
> >>
> >> No, trying to insert a module into a kernel built with the functionality
> >> compiled in is a vile perverted act, and probably illegal in Republican
> >> states! ;-)
> >>
> >> The other day I mentioned that reiser4 will find bugs because people
> >> will do bizarre things with it when it is more widely used. I think you
> >> have hit a "no one would ever do that" bug in the module loader, and
> >> demonstrated my point in the process.
> >>
> >> The panic isn't desirable, but I'm not sure what "correct behaviour"
> >> would be, I can't imagine that this is intended to work. The issues of
> >> removing such a module gracefully are significant.
> >
> >Wouldn't the desired behaviour be that when the kernel attempts to
> >load a module it checks if it is already present build-in and if so
> >simply refuse to load it at all?
>
> But that sounds just too easy to implement, what's the catch?  :o)

I've not looked at what it would take to do that, nor what measures
are currently in place, *at all*, but as I see it, all it would take
would be some "tag" present for each message stating if it was "build
in", or "currently loaded as a module", then on each module load check
the "tag" of the to-be-loaded module against the list of current
in-kernel tags, then reject if already on the list.
I can't see why there would be a catch...

--
Jesper Juhl <jesper.juhl@gmail.com>
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