From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EE8751D68D for ; Wed, 4 Oct 2023 18:24:17 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="rdcrP1Yy" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 28197C433CA; Wed, 4 Oct 2023 18:24:16 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1696443857; bh=Oy9DM5uBD3yP8eWGAuGeh203mOkDYvN2ojHksSipIac=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=rdcrP1YypI0pzeaFKgD2kSaH37NHJYH+jYT7M4CkcmHWlYyOYJ9yIZ9PQkeAtYhCT 4oOS94pf6Chwwwo6EYysXNH/H3cehqP4gNIMl1AuKddObSZROOA9zVoG/xwA9cCUVF +T4AeYkRb+8bNZ2wy9X3+/VwryXw+WsUYoKMEQkA= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Alexey Dobriyan , Kees Cook , Sasha Levin Subject: [PATCH 6.5 044/321] uapi: stddef.h: Fix __DECLARE_FLEX_ARRAY for C++ Date: Wed, 4 Oct 2023 19:53:09 +0200 Message-ID: <20231004175231.205660239@linuxfoundation.org> X-Mailer: git-send-email 2.42.0 In-Reply-To: <20231004175229.211487444@linuxfoundation.org> References: <20231004175229.211487444@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.5-stable review patch. If anyone has any objections, please let me know. ------------------ From: Alexey Dobriyan [ Upstream commit 32a4ec211d4164e667d9d0b807fadf02053cd2e9 ] __DECLARE_FLEX_ARRAY(T, member) macro expands to struct { struct {} __empty_member; T member[]; }; which is subtly wrong in C++ because sizeof(struct{}) is 1 not 0, changing UAPI structures layouts. This can be fixed by expanding to T member[]; Now g++ doesn't like "T member[]" either, throwing errors on the following code: struct S { union { T1 member1[]; T2 member2[]; }; }; or struct S { T member[]; }; Use "T member[0];" which seems to work and does the right thing wrt structure layout. Signed-off-by: Alexey Dobriyan Fixes: 3080ea5553cc ("stddef: Introduce DECLARE_FLEX_ARRAY() helper") Link: https://lore.kernel.org/r/97242381-f1ec-4a4a-9472-1a464f575657@p183 Signed-off-by: Kees Cook Signed-off-by: Sasha Levin --- include/uapi/linux/stddef.h | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/include/uapi/linux/stddef.h b/include/uapi/linux/stddef.h index c027b2070d790..5c6c4269f7efe 100644 --- a/include/uapi/linux/stddef.h +++ b/include/uapi/linux/stddef.h @@ -29,6 +29,11 @@ struct TAG { MEMBERS } ATTRS NAME; \ } +#ifdef __cplusplus +/* sizeof(struct{}) is 1 in C++, not 0, can't use C version of the macro. */ +#define __DECLARE_FLEX_ARRAY(T, member) \ + T member[0] +#else /** * __DECLARE_FLEX_ARRAY() - Declare a flexible array usable in a union * @@ -44,6 +49,7 @@ struct { } __empty_ ## NAME; \ TYPE NAME[]; \ } +#endif #ifndef __counted_by #define __counted_by(m) -- 2.40.1