linux-hardening - Re: [PATCH v2] overflow: Change DEFINE_FLEX to take __counted

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Date: Fri, 8 Mar 2024 20:20:18 +0000
From: Simon Horman <horms@...nel.org>
To: Kees Cook <keescook@...omium.org>
Cc: Przemek Kitszel <przemyslaw.kitszel@...el.com>,
	Jesse Brandeburg <jesse.brandeburg@...el.com>,
	Tony Nguyen <anthony.l.nguyen@...el.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org,
	linux-hardening@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] overflow: Change DEFINE_FLEX to take __counted_by
 member

On Wed, Mar 06, 2024 at 03:51:36PM -0800, Kees Cook wrote:
> The norm should be flexible array structures with __counted_by
> annotations, so DEFINE_FLEX() is updated to expect that. Rename
> the non-annotated version to DEFINE_RAW_FLEX(), and update the
> few existing users.
> 
> Signed-off-by: Kees Cook <keescook@...omium.org>

Hi Kees,

I'm unclear what this is based on, as it doesn't appear to apply
cleanly to net-next or the dev-queue branch of the iwl-next tree.
But I manually applied it to the latter and ran some checks.

...

> diff --git a/drivers/net/ethernet/intel/ice/ice_switch.c b/drivers/net/ethernet/intel/ice/ice_switch.c
> index f84bab80ca42..d4baae8c3b72 100644
> --- a/drivers/net/ethernet/intel/ice/ice_switch.c
> +++ b/drivers/net/ethernet/intel/ice/ice_switch.c

Given what is currently in the dev-queue branch of the iwl-next tree,
the following hunk also seems to be required for ice_switch.c.

@@ -5378,7 +5378,7 @@ ice_get_compat_fv_bitmap(struct ice_hw *hw, struct ice_adv_rule_info *rinfo,
  */
 static int ice_subscribe_recipe(struct ice_hw *hw, u16 rid)
 {
-	DEFINE_FLEX(struct ice_aqc_alloc_free_res_elem, sw_buf, elem, 1);
+	DEFINE_RAW_FLEX(struct ice_aqc_alloc_free_res_elem, sw_buf, elem, 1);
 	u16 buf_len = __struct_size(sw_buf);
 	u16 res_type;
 	int status;

...

> diff --git a/include/linux/overflow.h b/include/linux/overflow.h
> index aa691f2119b0..677b03c4c84f 100644
> --- a/include/linux/overflow.h
> +++ b/include/linux/overflow.h
> @@ -396,9 +396,9 @@ static inline size_t __must_check size_sub(size_t minuend, size_t subtrahend)
>   * @name: Name for a variable to define.
>   * @member: Name of the array member.
>   * @count: Number of elements in the array; must be compile-time const.
> - * @initializer: initializer expression (could be empty for no init).
> + * @initializer...: initializer expression (could be empty for no init).

Curiously kernel-doc --none seems happier without the line above changed.

>   */
> -#define _DEFINE_FLEX(type, name, member, count, initializer)			\
> +#define _DEFINE_FLEX(type, name, member, count, initializer...)			\
>  	_Static_assert(__builtin_constant_p(count),				\
>  		       "onstack flex array members require compile-time const count"); \
>  	union {									\

...