Re: Crypto Fixes for 4.12

From: David Miller
Date: Fri Jun 16 2017 - 12:50:05 EST

From: Theodore Ts'o <tytso@xxxxxxx>
Date: Fri, 16 Jun 2017 08:50:07 -0400

> On Thu, Jun 15, 2017 at 11:01:18AM -0400, David Miller wrote:
>> As a side note, ext4 does something similar with a private
>> implementation, but it doesn't use something the evaluates to an
>> alloca. Instead it uses a fixed 4-byte size for the shash context
>> value in the on-stack declaration.
> In ext4's case, we're doing it inside an inline function, and then
> using the "return" value from inside the calling function. Assuming
> that gcc actually inlines the function, are we in danger of tripping
> over the bug?

Again, the bug can only be triggered if you do a dynamically sized
object on the stack.

Which ext4 is not doing, since it uses fixed size elements in the
on-stack shash context.