linux-hardening - [PATCH] fortify: Do not cast to "unsigned char"

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Message-Id: <20221025231627.never.000-kees@kernel.org>
Date:   Tue, 25 Oct 2022 16:16:54 -0700
From:   Kees Cook <keescook@...omium.org>
To:     linux-hardening@...r.kernel.org
Cc:     Kees Cook <keescook@...omium.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH] fortify: Do not cast to "unsigned char"

Do not cast to "unsigned char", as this needlessly creates type problems
when attempting builds without -Wno-pointer-sign[1]. The intent of the
cast is to drop possible "const" types.

[1] https://lore.kernel.org/lkml/CAHk-=wgz3Uba8w7kdXhsqR1qvfemYL+OFQdefJnkeqXG8qZ_pA@mail.gmail.com/

Suggested-by: Linus Torvalds <torvalds@...ux-foundation.org>
Fixes: 3009f891bb9f ("fortify: Allow strlen() and strnlen() to pass compile-time known lengths")
Cc: Nick Desaulniers <ndesaulniers@...gle.com>
Cc: linux-hardening@...r.kernel.org
Signed-off-by: Kees Cook <keescook@...omium.org>
---
 include/linux/fortify-string.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/fortify-string.h b/include/linux/fortify-string.h
index f3dd5d1a6a25..09a032f6ce6b 100644
--- a/include/linux/fortify-string.h
+++ b/include/linux/fortify-string.h
@@ -18,7 +18,7 @@ void __write_overflow_field(size_t avail, size_t wanted) __compiletime_warning("
 
 #define __compiletime_strlen(p)					\
 ({								\
-	unsigned char *__p = (unsigned char *)(p);		\
+	char *__p = (char *)(p);				\
 	size_t __ret = SIZE_MAX;				\
 	size_t __p_size = __member_size(p);			\
 	if (__p_size != SIZE_MAX &&				\
-- 
2.34.1