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Message-ID: <CAA7aPHiEc_9pxEz+5JVH9g3U9jJ4-njJP8DkHirf6N0NL0MWbw@mail.gmail.com>
Date: Sun, 11 Jan 2015 11:31:55 -0500
From: stephen Turner <stephen.n.turner@...il.com>
To: musl@...ts.openwall.com
Subject: Re: Fixing multithreaded set*id() AS-safety
On Jan 10, 2015 11:07 PM, "Rich Felker" <dalias@...c.org> wrote:
>
> On Sat, Jan 10, 2015 at 05:52:45PM -0500, stephen Turner wrote:
> > Does that require any special requirementd in the way of modules or
> > settings to use from the kernel? If proc doesnt exist what will happen?
A
> > kernel panic, absence of threading or will it create the missing
folders or
> > such?
>
> No. As mentioned (I think) earlier, if /proc is not mounted,
> multi-threaded set*id would not be able to work, but would just report
> failure. Nothing would blow up. I'm not sure if it's a problem for
> multi-threaded set*id not to work without /proc mounted, but in
> general:
>
> - Various functions in musl already require /proc to operate correctly
> because the kernel does not provide a way to do the necessary
> operations without /proc. Some of these are less arcane than
> multi-threaded set*id.
>
> - It's rather a bad design to be calling setuid in a multi-threaded
> process to begin with; usually it happens only in Java or other
> "higher level" langs where you're calling out to setuid via some
> native interface and it's hard to prevent multiple threads from
> already existing at that point. These sorts of programs should not
> be running early boot before /proc is mounted.
>
> If failure when /proc is not mounted is really a problem, I'm not sure
> how we solve it. But in any case, I think we should start pushing for
> the kernel to fix this issue properly: with a syscall that affects all
> threads atomically, so that all this mess is used only as a fallback
> for old kernels.
>
> Rich
Thanks Rich for the details. You had mentioned it would fail but my
experience says that any failure leads to a system meltdown. Im not used to
failures not being the end of the world.
I include proc so for me theres no issue. I guess my devils advocate kicked
in.
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