Re: [PATCH] neighbour: Fix __randomize_layout crash in struct neighbour

[Gustavo A. R. Silva]

On 11/27/23 18:29, Kees Cook wrote:
> On Sat, Nov 25, 2023 at 03:33:58PM -0600, Gustavo A. R. Silva wrote:
> > Previously, one-element and zero-length arrays were treated as true
> > flexible arrays, even though they are actually "fake" flex arrays.
> > The __randomize_layout would leave them untouched at the end of the
> > struct, similarly to proper C99 flex-array members.
> >
> > However, this approach changed with commit 1ee60356c2dc ("gcc-plugins:
> > randstruct: Only warn about true flexible arrays"). Now, only C99
> > flexible-array members will remain untouched at the end of the struct,
> > while one-element and zero-length arrays will be subject to randomization.
> >
> > Fix a `__randomize_layout` crash in `struct neighbour` by transforming
> > zero-length array `primary_key` into a proper C99 flexible-array member.
> >
> > Fixes: 1ee60356c2dc ("gcc-plugins: randstruct: Only warn about true flexible arrays")
> > Closes: https://lore.kernel.org/linux-hardening/20231124102458.GB1503258@xxxxxxxxxxxxxxxxxxxxxxxxx/
> > Signed-off-by: Gustavo A. R. Silva <gustavoars@xxxxxxxxxx>
>
> Yes, please. Do we have any other 0-sized arrays hiding out in the
> kernel? We need to get these all cleared...

I've found 27 instances of zero-length fake-flex arrays in next-20231127.

I'll send a patch series to transform all of them.

> Reviewed-by: Kees Cook <keescook@xxxxxxxxxxxx>

Thanks!
--
Gustavo