linux-hardening - [PATCH v2 06/10] fortify: strcat: Move definition to use fortified strlcat()

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Date:   Fri,  7 Apr 2023 12:27:12 -0700
From:   Kees Cook <keescook@...omium.org>
To:     linux-hardening@...r.kernel.org
Cc:     Kees Cook <keescook@...omium.org>,
        "Andy Shevchenko" <andy@...nel.org>,
        "Cezary Rojewski" <cezary.rojewski@...el.com>,
        "Puyou Lu" <puyou.lu@...il.com>, "Mark Brown" <broonie@...nel.org>,
        "Josh Poimboeuf" <jpoimboe@...nel.org>,
        "Peter Zijlstra" <peterz@...radead.org>,
        "Brendan Higgins" <brendan.higgins@...ux.dev>,
        "David Gow" <davidgow@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Nathan Chancellor" <nathan@...nel.org>,
        "Alexander Potapenko" <glider@...gle.com>,
        "Zhaoyang Huang" <zhaoyang.huang@...soc.com>,
        "Randy Dunlap" <rdunlap@...radead.org>,
        "Geert Uytterhoeven" <geert+renesas@...der.be>,
        "Miguel Ojeda" <ojeda@...nel.org>,
        Alexander Lobakin <aleksander.lobakin@...el.com>,
        "Nick Desaulniers" <ndesaulniers@...gle.com>,
        "Liam Howlett" <liam.howlett@...cle.com>,
        "Vlastimil Babka" <vbabka@...e.cz>,
        "Dan Williams" <dan.j.williams@...el.com>,
        "Rasmus Villemoes" <linux@...musvillemoes.dk>,
        "Yury Norov" <yury.norov@...il.com>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        "Sander Vanheule" <sander@...nheule.net>,
        "Eric Biggers" <ebiggers@...gle.com>,
        "Masami Hiramatsu (Google)" <mhiramat@...nel.org>,
        "Andrey Konovalov" <andreyknvl@...il.com>,
        "Linus Walleij" <linus.walleij@...aro.org>,
        "Daniel Latypov" <dlatypov@...gle.com>,
        José Expósito <jose.exposito89@...il.com>,
        linux-kernel@...r.kernel.org, kunit-dev@...glegroups.com
Subject: [PATCH v2 06/10] fortify: strcat: Move definition to use fortified strlcat()

Move the definition of fortified strcat() to after strlcat() to use it
for bounds checking.

Signed-off-by: Kees Cook <keescook@...omium.org>
---
 include/linux/fortify-string.h | 53 +++++++++++++++++-----------------
 1 file changed, 26 insertions(+), 27 deletions(-)

diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h
index 8cf17ef81905..ab058d092817 100644
--- a/include/linux/fortify-string.h
+++ b/include/linux/fortify-string.h
@@ -151,33 +151,6 @@ char *strncpy(char * const POS p, const char *q, __kernel_size_t size)
 	return __underlying_strncpy(p, q, size);
 }
 
-/**
- * strcat - Append a string to an existing string
- *
- * @p: pointer to NUL-terminated string to append to
- * @q: pointer to NUL-terminated source string to append from
- *
- * Do not use this function. While FORTIFY_SOURCE tries to avoid
- * read and write overflows, this is only possible when the
- * destination buffer size is known to the compiler. Prefer
- * building the string with formatting, via scnprintf() or similar.
- * At the very least, use strncat().
- *
- * Returns @p.
- *
- */
-__FORTIFY_INLINE __diagnose_as(__builtin_strcat, 1, 2)
-char *strcat(char * const POS p, const char *q)
-{
-	const size_t p_size = __member_size(p);
-
-	if (p_size == SIZE_MAX)
-		return __underlying_strcat(p, q);
-	if (strlcat(p, q, p_size) >= p_size)
-		fortify_panic(__func__);
-	return p;
-}
-
 extern __kernel_size_t __real_strnlen(const char *, __kernel_size_t) __RENAME(strnlen);
 /**
  * strnlen - Return bounded count of characters in a NUL-terminated string
@@ -435,6 +408,32 @@ size_t strlcat(char * const POS p, const char * const POS q, size_t avail)
 	return wanted;
 }
 
+/* Defined after fortified strlcat() to reuse it. */
+/**
+ * strcat - Append a string to an existing string
+ *
+ * @p: pointer to NUL-terminated string to append to
+ * @q: pointer to NUL-terminated source string to append from
+ *
+ * Do not use this function. While FORTIFY_SOURCE tries to avoid
+ * read and write overflows, this is only possible when the
+ * destination buffer size is known to the compiler. Prefer
+ * building the string with formatting, via scnprintf() or similar.
+ * At the very least, use strncat().
+ *
+ * Returns @p.
+ *
+ */
+__FORTIFY_INLINE __diagnose_as(__builtin_strcat, 1, 2)
+char *strcat(char * const POS p, const char *q)
+{
+	const size_t p_size = __member_size(p);
+
+	if (strlcat(p, q, p_size) >= p_size)
+		fortify_panic(__func__);
+	return p;
+}
+
 /**
  * strncat - Append a string to an existing string
  *
-- 
2.34.1