Re: +core_pattern-set-core-helpers-root-and-namespace-to-crashing-process .patchadded to -mm tree

From: Neil Horman
Date: Tue Dec 18 2012 - 15:19:20 EST

On Tue, Dec 18, 2012 at 09:06:04PM +0100, Oleg Nesterov wrote:
> On 12/17, Neil Horman wrote:
> >
> > On Mon, Dec 17, 2012 at 05:04:08PM +0100, Oleg Nesterov wrote:
> > >
> > > > Is there a way to switch all namespaces, except for the pid
> > > > namespace?
> > >
> > > Which exactly namespaces you want to change?
> > >
> > Ideally, I want the pipe reader process to execute in the same namespaces that
> > the crashing process executed in (i.e. the pipe reader should execute as though
> > the crashing process forked it).
> Yes, and we probably want to change pid_ns as well. But afaics currently
> this is not possible, even setns can't do this.
> I am starting to think that in this case, perhaps, do_coredump() should
> not use call_usermode_helper() at all. Perhaps we can do clone(CLONE_VM) +
> commit_creds/restore_root/etc + kernel_execve.
Yeah, I was comming to this same conclusion last night as well. I'd rather keep
using the call_usermode_helper solution if at all possible, but perhaps we can
integrate a clone path into it.

> > > To be honest, I do not understand this patch at all. It seems that
> > > you need to do something like sys_setns(). But if we do this, then
> > > why we can't make core_pattern per-namespace?
> > >
> > That actually would make sense, although we can't really use setns directly, as
> > I don't think we want to open file descriptors to do this manipulation in the
> > kernel.
> Yes, yes, sure. But this is solveable. We do not really need to open
> the files in /proc, we could use proc_ns_operations->install() directly.
> Although this is not pretty.
Its not pretty, no. If we use the above clone solution however, we can avoid
this entirely.

> > Perhaps its best just to restrict this patch to adjusting the root fs location
> > for the chroot case.
> Probably... at least for the start.
> BTW. Of course this is subjective, but personally I think that "||"
> looks strange. Perhaps it would be better to add something like
> --croot argument?
The || is ambiguous with its simmilarity to a shell 'or' command, but I don't
think the --croot argument is much better on that front, as that then becomes
ambiguous with arguments supplied to the pipe reader directly. The token should
be leading the pipe_reader string in core_pattern to indicate a change in
environment independent of the executable path. Perhaps |^ or something

Either way, Andrew, could you please drop this patch? Olegs comments I think
make it pretty clear I've got some more work to do on this.


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