[PATCH] security: keys: Use kvfree_sensitive in a few places

[Alex Dewar]

On Fri, Sep 11, 2020 at 08:04:24AM -0700, James Bottomley wrote:
> On Fri, 2020-09-11 at 12:44 +0100, Alex Dewar wrote:
> > In big_key.c, there are a few places where memzero_explicit + kvfree
> > is used. It is better to use kvfree_sensitive instead, which is more
> > readable and also prevents the compiler from eliding the call to
> > memzero_explicit. Fix this.
> 
> That last bit is untrue: the compiler can't elide memzero_explicit ...
> that's why it has the explicit suffix.
> 
> The original problem was a lot of people do memset(.., 0, ..); kfree()
> which the compiler can elide if it understands the memory is going out
> of scope.  Or the even more problematic memset(..., 0, ...) on a stack
> variable before it goes out of scope.
> 
> We can argue about readability but there's no secret leak here.

Ahh, my mistake. Thanks for the explanation.

I'll send a v2 with an updated commit message. I think it would still
make sense to use kfree_sensitive here as on next-20200911 this is the
last use of kzfree in the tree and it would be nice to excise it
altogether.

Best,
Alex

> 
> James
>