Re: Fixing multithreaded set*id() AS-safety

[stephen Turner <stephen.n.turner@gmail.com>]

[-- Attachment #1: Type: text/plain, Size: 1875 bytes --]

On Jan 10, 2015 11:07 PM, "Rich Felker" <dalias@libc.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.

[-- Attachment #2: Type: text/html, Size: 2302 bytes --]