linux-hardening - Re: [PATCH] xfrm: Annotate struct xfrm_sec_ctx with __counted

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Date: Wed, 4 Oct 2023 01:38:50 +0200
From: "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To: Kees Cook <keescook@...omium.org>,
 Steffen Klassert <steffen.klassert@...unet.com>
Cc: Herbert Xu <herbert@...dor.apana.org.au>,
 "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
 "Gustavo A. R. Silva" <gustavoars@...nel.org>,
 Nathan Chancellor <nathan@...nel.org>,
 Nick Desaulniers <ndesaulniers@...gle.com>, Tom Rix <trix@...hat.com>,
 linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org,
 llvm@...ts.linux.dev
Subject: Re: [PATCH] xfrm: Annotate struct xfrm_sec_ctx with __counted_by



On 10/4/23 01:18, Kees Cook wrote:
> Prepare for the coming implementation by GCC and Clang of the __counted_by
> attribute. Flexible array members annotated with __counted_by can have
> their accesses bounds-checked at run-time via CONFIG_UBSAN_BOUNDS (for
> array indexing) and CONFIG_FORTIFY_SOURCE (for strcpy/memcpy-family
> functions).
> 
> As found with Coccinelle[1], add __counted_by for struct xfrm_sec_ctx.
> 
> Cc: Steffen Klassert <steffen.klassert@...unet.com>
> Cc: Herbert Xu <herbert@...dor.apana.org.au>
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: netdev@...r.kernel.org
> Link: https://github.com/kees/kernel-tools/blob/trunk/coccinelle/examples/counted_by.cocci [1]
> Signed-off-by: Kees Cook <keescook@...omium.org>

Reviewed-by: Gustavo A. R. Silva <gustavoars@...nel.org>

Thanks
--
Gustavo

> ---
>   include/uapi/linux/xfrm.h | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/include/uapi/linux/xfrm.h b/include/uapi/linux/xfrm.h
> index 23543c33fee8..6a77328be114 100644
> --- a/include/uapi/linux/xfrm.h
> +++ b/include/uapi/linux/xfrm.h
> @@ -4,6 +4,7 @@
>   
>   #include <linux/in6.h>
>   #include <linux/types.h>
> +#include <linux/stddef.h>
>   
>   /* All of the structures in this file may not change size as they are
>    * passed into the kernel from userspace via netlink sockets.
> @@ -33,7 +34,7 @@ struct xfrm_sec_ctx {
>   	__u8	ctx_alg;
>   	__u16	ctx_len;
>   	__u32	ctx_sid;
> -	char	ctx_str[];
> +	char	ctx_str[] __counted_by(ctx_len);
>   };
>   
>   /* Security Context Domains of Interpretation */