linux-kernel - Re: [PATCH v2] wireguard: Add __nonstring annotations for unterminated strings

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Message-ID: <20250318130811.GQ688833@kernel.org>
Date: Tue, 18 Mar 2025 13:08:11 +0000
From: Simon Horman <horms@...nel.org>
To: Kees Cook <kees@...nel.org>
Cc: "Jason A . Donenfeld" <Jason@...c4.com>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	wireguard@...ts.zx2c4.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2] wireguard: Add __nonstring annotations for
 unterminated strings

On Wed, Mar 12, 2025 at 01:14:51PM -0700, Kees Cook wrote:
> When a character array without a terminating NUL character has a static
> initializer, GCC 15's -Wunterminated-string-initialization will only
> warn if the array lacks the "nonstring" attribute[1]. Mark the arrays
> with __nonstring to correctly identify the char array as "not a C string"
> and thereby eliminate the warning:
> 
> ../drivers/net/wireguard/cookie.c:29:56: warning: initializer-string for array of 'unsigned char' truncates NUL terminator but destination lacks 'nonstring' attribute (9 chars into 8 available) [-Wunterminated-string-initialization]
>    29 | static const u8 mac1_key_label[COOKIE_KEY_LABEL_LEN] = "mac1----";
>       |                                                        ^~~~~~~~~~
> ../drivers/net/wireguard/cookie.c:30:58: warning: initializer-string for array of 'unsigned char' truncates NUL terminator but destination lacks 'nonstring' attribute (9 chars into 8 available) [-Wunterminated-string-initialization]
>    30 | static const u8 cookie_key_label[COOKIE_KEY_LABEL_LEN] = "cookie--";
>       |                                                          ^~~~~~~~~~
> ../drivers/net/wireguard/noise.c:28:38: warning: initializer-string for array of 'unsigned char' truncates NUL terminator but destination lacks 'nonstring' attribute (38 chars into 37 available) [-Wunterminated-string-initialization]
>    28 | static const u8 handshake_name[37] = "Noise_IKpsk2_25519_ChaChaPoly_BLAKE2s";
>       |                                      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> ../drivers/net/wireguard/noise.c:29:39: warning: initializer-string for array of 'unsigned char' truncates NUL terminator but destination lacks 'nonstring' attribute (35 chars into 34 available) [-Wunterminated-string-initialization]
>    29 | static const u8 identifier_name[34] = "WireGuard v1 zx2c4 Jason@...c4.com";
>       |                                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> The arrays are always used with their fixed size, so use __nonstring.
> 
> Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117178 [1]
> Signed-off-by: Kees Cook <kees@...nel.org>
> ---
>  v2: Improve commit log, add cookie nonstrings too
>  v1: https://lore.kernel.org/lkml/20250310222249.work.154-kees@kernel.org/

Reviewed-by: Simon Horman <horms@...nel.org>