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From:   Bill Wendling <morbo@google.com>
Date:   Mon, 7 Aug 2023 15:36:55 -0700
Message-ID: <CAGG=3QVUqVdkzBo-=vGWprPBUhuV8p3bRSx3Qsvtqx_LDct05w@mail.gmail.com>
Subject: Re: [PATCH] um: refactor deprecated strncpy to strtomem
To:     Justin Stitt <justinstitt@google.com>
Cc:     Richard Weinberger <richard@nod.at>,
        Anton Ivanov <anton.ivanov@cambridgegreys.com>,
        Johannes Berg <johannes@sipsolutions.net>,
        linux-hardening@vger.kernel.org, linux-um@lists.infradead.org,
        linux-kernel@vger.kernel.org, Kees Cook <keescook@chromium.org>
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On Mon, Aug 7, 2023 at 2:18=E2=80=AFPM Justin Stitt <justinstitt@google.com=
> wrote:
>
> Use `strtomem` here since `console_buf` is not expected to be
> NUL-terminated. We should probably also just use `MCONSOLE_MAX_DATA`
> instead of using `ARRAY_SIZE()` for every iteration of the loop.
>
Is this change necessary? I have a general preference for ARRAY_SIZE,
because a change in size is less likely to be overlooked (unless that
goes against the coding standard).

> Also mark char buffer as `__nonstring` as per Kees' suggestion here [1]
>
> Finally, follow checkpatch's recommendation of using `min_t` over `min`
>
> Link: https://github.com/KSPP/linux/issues/90 [1]
> Cc: linux-hardening@vger.kernel.org
> Signed-off-by: Justin Stitt <justinstitt@google.com>
> ---
> Notes:
> I only build tested this patch.
> ---
>  arch/um/drivers/mconsole_kern.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/arch/um/drivers/mconsole_kern.c b/arch/um/drivers/mconsole_k=
ern.c
> index 5026e7b9adfe..fd4c024202ae 100644
> --- a/arch/um/drivers/mconsole_kern.c
> +++ b/arch/um/drivers/mconsole_kern.c
> @@ -4,6 +4,7 @@
>   * Copyright (C) 2001 - 2008 Jeff Dike (jdike@{addtoit,linux.intel}.com)
>   */
>
> +#include "linux/compiler_attributes.h"

nit: Should this include be in angle brackets?

#include <linux/compiler_attributes.h>

>  #include <linux/console.h>
>  #include <linux/ctype.h>
>  #include <linux/string.h>
> @@ -554,7 +555,7 @@ struct mconsole_output {
>
>  static DEFINE_SPINLOCK(client_lock);
>  static LIST_HEAD(clients);
> -static char console_buf[MCONSOLE_MAX_DATA];
> +static char console_buf[MCONSOLE_MAX_DATA] __nonstring;
>
>  static void console_write(struct console *console, const char *string,
>                           unsigned int len)
> @@ -566,8 +567,8 @@ static void console_write(struct console *console, co=
nst char *string,
>                 return;
>
>         while (len > 0) {
> -               n =3D min((size_t) len, ARRAY_SIZE(console_buf));
> -               strncpy(console_buf, string, n);
> +               n =3D min_t(size_t, len, MCONSOLE_MAX_DATA);
> +               strtomem(console_buf, string);
>                 string +=3D n;
>                 len -=3D n;
>
>
> ---
> base-commit: c1a515d3c0270628df8ae5f5118ba859b85464a2
> change-id: 20230807-arch-um-3ef24413427e
>
> Best regards,
> --
> Justin Stitt <justinstitt@google.com>
>