Re: [PATCH] pidns: remove recursion from free_pid_ns() v5

[Andrew Morton]

On Thu, 11 Oct 2012 00:42:56 +0400
Cyrill Gorcunov <gorcunov@xxxxxxxxxx> wrote:

> The free_pid_ns function done in recursion fashion:
> 
> free_pid_ns(parent)
>   put_pid_ns(parent)
>     kref_put(&ns->kref, free_pid_ns);
>       free_pid_ns
> 
> thus if there was a huge nesting of namespaces the userspace
> may trigger avalanche calling of free_pid_ns leading to
> kernel stack exhausting and a panic eventually.
> 
> This patch turns the recursion into iterative loop.
> 
> v5 (from oleg@):
>  - Drop @ret variable
>  - Make put_pid_ns non-inline since it grows in size,
>    in turn make free_pid_ns static

OK, let's try that.  I'll sit on this until -rc2 to give it a bit of
time to cook.

A -stable backport might be needed.  What capabilities does userspace
need to be able to trigger the kernel stack overflow?
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