linux-hardening - Re: [PATCH v2] string: Introduce strtomem() and strtomem

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Date:   Fri, 2 Sep 2022 11:21:21 +0700
From:   Bagas Sanjaya <bagasdotme@...il.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Geert Uytterhoeven <geert@...ux-m68k.org>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Guenter Roeck <linux@...ck-us.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jonathan Corbet <corbet@....net>,
        Len Baker <len.baker@....com>,
        "Gustavo A. R. Silva" <gustavoars@...nel.org>,
        Francis Laniel <laniel_francis@...vacyrequired.com>,
        Paolo Abeni <pabeni@...hat.com>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2] string: Introduce strtomem() and strtomem_pad()

On Thu, Sep 01, 2022 at 12:09:52PM -0700, Kees Cook wrote:
> + * Do not use this function. While FORTIFY_SOURCE tries to avoid
> + * over-reads of @q, it cannot defend against writing unterminated
> + * results to @p. Using strncpy() remains ambiguous and fragile.
> + * Instead, please choose an alternative, so that the expectation
> + * of @p's contents is unambiguous:
> + *
> + * @p needs to be:     | padded to @size | not padded
> + * --------------------+-----------------+------------+
> + *      NUL-terminated | strscpy_pad()   | strscpy()  |
> + * --------------------+-----------------+------------+
> + *  not NUL-terminated | strtomem_pad()  | strtomem() |
> + * --------------------+-----------------+------------+
> + *

My htmldocs build doesn't catch any new warnings, but I think the table
above can be fixed up:

---- >8 ----

diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h
index eed2119b23c523..3413a8e561fc62 100644
--- a/include/linux/fortify-string.h
+++ b/include/linux/fortify-string.h
@@ -95,12 +95,13 @@ extern char *__underlying_strncpy(char *p, const char *q, __kernel_size_t size)
  * Instead, please choose an alternative, so that the expectation
  * of @p's contents is unambiguous:
  *
- * @p needs to be:     | padded to @size | not padded
- * --------------------+-----------------+------------+
- *      NUL-terminated | strscpy_pad()   | strscpy()  |
- * --------------------+-----------------+------------+
- *  not NUL-terminated | strtomem_pad()  | strtomem() |
- * --------------------+-----------------+------------+
+ * +--------------------+-----------------+------------+
+ * |@p needs to be:     | padded to @size | not padded |
+ * +====================+=================+============+
+ * |     NUL-terminated | strscpy_pad()   | strscpy()  |
+ * +--------------------+-----------------+------------+
+ * | not NUL-terminated | strtomem_pad()  | strtomem() |
+ * +--------------------+-----------------+------------+
  *
  * Note strscpy*()'s differing return values for detecting truncation,
  * and strtomem*()'s expectation that the destination is marked with

> + * Note strscpy*()'s differing return values for detecting truncation,
> + * and strtomem*()'s expectation that the destination is marked with
> + * __nonstring when it is a character array.
> + *

Regardless, I don't see these new table above in the output (am I missing
something?).

Thanks.

-- 
An old man doll... just what I always wanted! - Clara

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