linux-kernel - Re: [PATCH v2] rslib: Remove VLAs by setting upper bound on nroots

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Message-Id: <20180316155950.35fda7c63ec59277ba504201@linux-foundation.org>
Date:   Fri, 16 Mar 2018 15:59:50 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     linux-kernel@...r.kernel.org,
        Segher Boessenkool <segher@...nel.crashing.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        kernel-hardening@...ts.openwall.com
Subject: Re: [PATCH v2] rslib: Remove VLAs by setting upper bound on nroots

On Thu, 15 Mar 2018 15:59:19 -0700 Kees Cook <keescook@...omium.org> wrote:

> Avoid stack VLAs[1] by always allocating the upper bound of stack space
> needed. The existing users of rslib appear to max out at 24 roots[2],
> so use that as the upper bound until we have a reason to change it.
> 
> Alternative considered: make init_rs() a true caller-instance and
> pre-allocate the workspaces. This would possibly need locking and
> a refactoring of the returned structure.
> 
> Using kmalloc in this path doesn't look great, especially since at
> least one caller (pstore) is sensitive to allocations during rslib
> usage (it expects to run it during an Oops, for example).

Oh.

Could we allocate the storage during init_rs(), attach it to `struct
rs_control'?