linux-hardening - Re: [PATCH] ima: Add __counted_by for struct modsig and use struct

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Message-ID: <202310091255.FCA0DB3C1@keescook>
Date: Mon, 9 Oct 2023 12:55:24 -0700
From: Kees Cook <keescook@...omium.org>
To: "Gustavo A. R. Silva" <gustavoars@...nel.org>
Cc: Mimi Zohar <zohar@...ux.ibm.com>,
	Dmitry Kasatkin <dmitry.kasatkin@...il.com>,
	Paul Moore <paul@...l-moore.com>, James Morris <jmorris@...ei.org>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	linux-integrity@...r.kernel.org,
	linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH] ima: Add __counted_by for struct modsig and use
 struct_size()

On Mon, Oct 09, 2023 at 01:52:45PM -0600, Gustavo A. R. Silva 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).
> 
> Also, relocate `hdr->raw_pkcs7_len = sig_len;` so that the __counted_by
> annotation has effect, and flex-array member `raw_pkcs7` can be properly
> bounds-checked at run-time.
> 
> While there, use struct_size() helper, instead of the open-coded
> version, to calculate the size for the allocation of the whole
> flexible structure, including of course, the flexible-array member.
> 
> This code was found with the help of Coccinelle, and audited and
> fixed manually.
> 
> Signed-off-by: Gustavo A. R. Silva <gustavoars@...nel.org>

Looks right; good catch on moving the assignment.

Reviewed-by: Kees Cook <keescook@...omium.org>

-- 
Kees Cook