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Message-ID: <202308311411.B2B57B7441@keescook>
Date: Thu, 31 Aug 2023 14:19:28 -0700
From: Kees Cook <keescook@...omium.org>
To: Justin Stitt <justinstitt@...gle.com>
Cc: Nathan Chancellor <nathan@...nel.org>,
Nick Desaulniers <ndesaulniers@...gle.com>,
Tom Rix <trix@...hat.com>, linux-kernel@...r.kernel.org,
llvm@...ts.linux.dev
Subject: Re: [PATCH RFC] init: fix -Wmissing-variable-declarations warning
On Tue, Aug 29, 2023 at 11:38:31PM +0000, Justin Stitt wrote:
> Hi all,
>
> I was looking to get some help on solving this -Wmissing-variable-declarations
> warning as there is some hope to turn it on for W=1 soon [1].
>
> When building x86/defconfig with Clang-18 I encounter the following warning:
> | init/main.c:189:13: warning: no previous extern declaration for non-static variable 'envp_init' [-Wmissing-variable-declarations]
> | 189 | const char *envp_init[MAX_INIT_ENVS+2] = { "HOME=/", "TERM=linux", NULL, };
> | | ^
> | init/main.c:189:7: note: declare 'static' if the variable is not intended to be used outside of this translation unit
> | 189 | const char *envp_init[MAX_INIT_ENVS+2] = { "HOME=/", "TERM=linux", NULL, };
> | | ^
>
> It seems like the obvious solution is to just add the `static` keyword
> and be done with it. I suspect, however, that it is not so simple for
> the following reasons:
>
> Firstly, `envp_init` is surrounded by two other variables that have been
> explicitly marked as `static` which leads me to believe that this one
> was intentionally _not_ marked as static for some reason:
> | static const char *argv_init[MAX_INIT_ARGS+2] = { "init", NULL, };
> | static const char *envp_init[MAX_INIT_ENVS+2] = { "HOME=/", "TERM=linux", NULL, };
> | static const char *panic_later, *panic_param;
I went looking to see the history here and it goes beyond git history. :)
>
> Secondly, there exists this `extern` declaration for `envp_init`:
> | init/do_mounts_initrd.c
> | 90: extern char *envp_init[];
This is the only user of call_usermodehelper_setup() that doesn't make
its own envp. And there's a deprecation warning in that function too:
9acc17baf1fd6 (Christoph Hellwig 2020-07-08 18:18:54 +0200 93) pr_warn("using deprecated initrd support, will be removed in 2021.\n");
> Any help here would be appreciated!
I recommend making it static and giving handle_initrd() its own copy:
diff --git a/init/do_mounts_initrd.c b/init/do_mounts_initrd.c
index 425f4bcf4b77..154bd0de85a6 100644
--- a/init/do_mounts_initrd.c
+++ b/init/do_mounts_initrd.c
@@ -87,7 +87,7 @@ static void __init handle_initrd(char *root_device_name)
{
struct subprocess_info *info;
static char *argv[] = { "linuxrc", NULL, };
- extern char *envp_init[];
+ static char *envp[] = { "HOME=/", "TERM=linux", NULL, };
int error;
pr_warn("using deprecated initrd support, will be removed in 2021.\n");
@@ -100,7 +100,7 @@ static void __init handle_initrd(char *root_device_name)
init_mkdir("/old", 0700);
init_chdir("/old");
- info = call_usermodehelper_setup("/linuxrc", argv, envp_init,
+ info = call_usermodehelper_setup("/linuxrc", argv, envp,
GFP_KERNEL, init_linuxrc, NULL, NULL);
if (!info)
return;
--
Kees Cook
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