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SubjectRe: Allocation of too much memory hangs system, kernel 2.2.*
Date
Followup to:  <Pine.LNX.4.10.9906010942170.3302-100000@cola.svenskatest.se>
By author: Urban Widmark <urban@svenskatest.se>
In newsgroup: linux.dev.kernel
>
> It is perhaps not possible to kill init, but the kernel can stop init from
> working (if it was actually killed or not ...). The effects I've seen is
> that all processes that die end up as zombies and shutdown/reboot/halt
> stop working.
>
> I don't remember if I reported it or not, since I thought the "OOM"
> problem was well known and left for future Linux versions.
> (there were a lot of "OOM killer patches" that Andrea et al threw at each
> other, around late 2.1.1xx :)
>
> Some old(?) version of postgresql didn't like a sql statement of mine and
> decided it needed lots of memory to optimize/parse it. That killed almost
> everything on the machine (2.2.0 or 2.2.0-preX), I telnet'ed back and
> there were zombies everywhere.
> I didn't save the logfiles either, if init was killed the oom() should
> have logged that.
>
> And just to be sure I re-ran the same sql after rebooting and again random
> processes were killed, but this time init was not killed/stopped/...
>
>
> mm/memory.c does, on a task failing to 'put_dirty_page'
> force_sig(SIGKILL, task);
> which (I think) leads to
> force_sig_info(sig, (void*)1L, p);
> return send_sig_info(sig, info, t);
>
> Then there is a permissions check with lots of && expressions, where
> info == 1L
> This part is then not true, so the operation is allowed
> (!info || ((unsigned long)info != 1 && SI_FROMUSER(info))
>
> And then I'm lost ... I can't find where the kernel is stopped from
> killing init.
>
>
> I suppose I should provide better debugging info by repeatedly killing a
> machine (with a recent 2.2 kernel) until I manage to hit init, if that is
> possible.
>

It's possible there is a bug in the check here. If so, we should fix
it. It would be bad for the kernel to kill init under any
circumstances.

-hpa
--
"The user's computer downloads the ActiveX code and simulates a 'Blue
Screen' crash, a generally benign event most users are familiar with
and that would not necessarily arouse suspicions."
-- Security exploit description on http://www.zks.net/p3/how.asp

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