linux-kernel - Re: [PATCH 3/5] module: Restore the moduleparam prefix length check

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Message-ID: <15f52f4c-7809-46ab-9e13-bd487f35a80c@kernel.org>
Date: Thu, 17 Jul 2025 21:23:56 +0200
From: Daniel Gomez <da.gomez@...nel.org>
To: Petr Pavlu <petr.pavlu@...e.com>, Luis Chamberlain <mcgrof@...nel.org>,
 Sami Tolvanen <samitolvanen@...gle.com>, Daniel Gomez <da.gomez@...sung.com>
Cc: linux-modules@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/5] module: Restore the moduleparam prefix length check

On 30/06/2025 16.32, Petr Pavlu wrote:
> The moduleparam code allows modules to provide their own definition of
> MODULE_PARAM_PREFIX, instead of using the default KBUILD_MODNAME ".".
> 
> Commit 730b69d22525 ("module: check kernel param length at compile time,
> not runtime") added a check to ensure the prefix doesn't exceed
> MODULE_NAME_LEN, as this is what param_sysfs_builtin() expects.
> 
> Later, commit 58f86cc89c33 ("VERIFY_OCTAL_PERMISSIONS: stricter checking
> for sysfs perms.") removed this check, but there is no indication this was
> intentional.
> 
> Since the check is still useful for param_sysfs_builtin() to function
> properly, reintroduce it in __module_param_call(), but in a modernized form
> using static_assert().
> 
> While here, clean up the __module_param_call() comments. In particular,
> remove the comment "Default value instead of permissions?", which comes
> from commit 9774a1f54f17 ("[PATCH] Compile-time check re world-writeable
> module params"). This comment was related to the test variable
> __param_perm_check_##name, which was removed in the previously mentioned
> commit 58f86cc89c33.
> 
> Fixes: 58f86cc89c33 ("VERIFY_OCTAL_PERMISSIONS: stricter checking for sysfs perms.")
> Signed-off-by: Petr Pavlu <petr.pavlu@...e.com>
> ---
>  include/linux/moduleparam.h | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/moduleparam.h b/include/linux/moduleparam.h
> index bfb85fd13e1f..110e9d09de24 100644
> --- a/include/linux/moduleparam.h
> +++ b/include/linux/moduleparam.h
> @@ -282,10 +282,9 @@ struct kparam_array
>  #define __moduleparam_const const
>  #endif
>  
> -/* This is the fundamental function for registering boot/module
> -   parameters. */
> +/* This is the fundamental function for registering boot/module parameters. */
>  #define __module_param_call(prefix, name, ops, arg, perm, level, flags)	\
> -	/* Default value instead of permissions? */			\
> +	static_assert(sizeof(""prefix) - 1 <= MAX_PARAM_PREFIX_LEN);	\

Can you clarify if -1 to remove the dot from prefix?

Final code 
	static_assert(sizeof(""prefix) - 1 <= __MODULE_NAME_LEN);	\

with __MODULE_NAME_LEN being:

#define __MODULE_NAME_LEN (64 - sizeof(unsigned long))


>  	static const char __param_str_##name[] = prefix #name;		\
>  	static struct kernel_param __moduleparam_const __param_##name	\
>  	__used __section("__param")					\