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Date: Mon, 12 Mar 2018 16:26:39 +1100
From: "Tobin C. Harding" <>
To: Kees Cook <>, Tycho Andersen <>
Subject: VLA commit log


I got some push back on the commit log we have all started to use
(copying Kees' initial commit log).  If we are going to do hundreds of
these patches should we write a perfectly correct commit log that can be
included as the start of the 'why' of each VLA removal patch?  Here is
my attempt, I am quite bad at writing commit logs so would love someone
to fix it up.

    Kernel stack size is limited.  Variable Length Arrays (VLA) open the
    kernel up to stack abuse in a couple of ways;
    1. If the variable can be controlled by an attacker.
    2. Not having the size of the stack right there in plain site makes it
    harder to maintain the code base because changes in one place can effect
    the stack in another place (i.e in another function).
    It would be nice to be able to build the kernel with -Wvla.  There has
    been some consensus on this already [1].



The '...' would of course be different for each patch.  In case you
missed it here is the catalyst for this email

	On Mon, Mar 12, 2018 at 03:49:40PM +1100, Tobin C. Harding wrote:
	> The kernel would like to have all stack VLA usage removed[1].

	Can you please stop writing this?  The Linux kernel isn't
	sentient; it doesn't "like" anything.  You need to explain why
	*you* (and other people) believe these changes should be made.

Perhaps we should add a summary of all the gcc discussion i.e why const
variables still cause gcc to emit a VLA warning.


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