linux-hardening - Re: [PATCH] ACPICA: Replace fake flexible arrays with flexible array members

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Date:   Sun, 15 Jan 2023 10:38:48 -0800
From:   Kees Cook <keescook@...omium.org>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     Len Brown <lenb@...nel.org>, Robert Moore <robert.moore@...el.com>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        linux-acpi@...r.kernel.org, devel@...ica.org,
        linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] ACPICA: Replace fake flexible arrays with flexible array
 members

On Fri, Nov 18, 2022 at 10:15:51AM -0800, Kees Cook wrote:
> Functionally identical to ACPICA upstream pull request 813:
> https://github.com/acpica/acpica/pull/813

Any update on this? Upstream is currently unbuildable since October.

> One-element arrays (and multi-element arrays being treated as
> dynamically sized) are deprecated[1] and are being replaced with
> flexible array members in support of the ongoing efforts to tighten the
> FORTIFY_SOURCE routines on memcpy(), correctly instrument array indexing
> with UBSAN_BOUNDS, and to globally enable -fstrict-flex-arrays=3.
> 
> Replace one-element array with flexible-array member in struct
> acpi_resource_extended_irq. Replace 4-byte fixed-size array with 4-byte
> padding in a union with a flexible-array member in struct
> acpi_pci_routing_table.
> 
> This results in no differences in binary output.

In the meantime, can you take this patch for Linux, and we can wait for
ACPICA to catch up?

Thanks!

-Kees

> 
> Cc: "Rafael J. Wysocki" <rafael@...nel.org>
> Cc: Len Brown <lenb@...nel.org>
> Cc: Robert Moore <robert.moore@...el.com>
> Cc: "Gustavo A. R. Silva" <gustavoars@...nel.org>
> Cc: linux-acpi@...r.kernel.org
> Cc: devel@...ica.org
> Signed-off-by: Kees Cook <keescook@...omium.org>
> ---
>  include/acpi/acrestyp.h | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/include/acpi/acrestyp.h b/include/acpi/acrestyp.h
> index a7fb8ddb3dc6..ee945084d46e 100644
> --- a/include/acpi/acrestyp.h
> +++ b/include/acpi/acrestyp.h
> @@ -332,7 +332,7 @@ struct acpi_resource_extended_irq {
>  	u8 wake_capable;
>  	u8 interrupt_count;
>  	struct acpi_resource_source resource_source;
> -	u32 interrupts[1];
> +	u32 interrupts[];
>  };
>  
>  struct acpi_resource_generic_register {
> @@ -679,7 +679,10 @@ struct acpi_pci_routing_table {
>  	u32 pin;
>  	u64 address;		/* here for 64-bit alignment */
>  	u32 source_index;
> -	char source[4];		/* pad to 64 bits so sizeof() works in all cases */
> +	union {
> +		char pad[4];	/* pad to 64 bits so sizeof() works in all cases */
> +		DECLARE_FLEX_ARRAY(char, source);
> +	};
>  };
>  
>  #endif				/* __ACRESTYP_H__ */
> -- 
> 2.34.1
> 

-- 
Kees Cook