linux-kernel - Re: [PATCH] security: declare member holding string literal const

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Date:   Thu, 17 Feb 2022 14:50:25 -0800
From:   Casey Schaufler <casey@...aufler-ca.com>
To:     Christian Göttsche <cgzones@...glemail.com>,
        selinux@...r.kernel.org
Cc:     James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Paul Moore <paul@...l-moore.com>,
        Xin Long <lucien.xin@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Ondrej Mosnacek <omosnace@...hat.com>,
        Mickaël Salaün <mic@...ux.microsoft.com>,
        Todd Kjos <tkjos@...gle.com>,
        Olga Kornievskaia <kolga@...app.com>,
        linux-kernel@...r.kernel.org,
        linux-security-module@...r.kernel.org, llvm@...ts.linux.dev,
        Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: [PATCH] security: declare member holding string literal const

On 2/17/2022 6:18 AM, Christian Göttsche wrote:
> The struct security_hook_list member lsm is assigned in
> security_add_hooks() with string literals passed from the individual
> security modules.  Declare the function parameter and the struct member
> const to signal their immutability.
>
> Reported by Clang [-Wwrite-strings]:
>
>      security/selinux/hooks.c:7388:63: error: passing 'const char [8]' to parameter of type 'char *' discards qualifiers [-Werror,-Wincompatible-pointer-types-discards-qualifiers]
>              security_add_hooks(selinux_hooks, ARRAY_SIZE(selinux_hooks), selinux);
>                                                                           ^~~~~~~~~
>      ./include/linux/lsm_hooks.h:1629:11: note: passing argument to parameter 'lsm' here
>                                      char *lsm);
>                                            ^
>
> Signed-off-by: Christian Göttsche <cgzones@...glemail.com>

Reviewed-by: Casey Schaufler <casey@...aufler-ca.com>

> ---
>   include/linux/lsm_hooks.h | 4 ++--
>   security/security.c       | 2 +-
>   2 files changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
> index 419b5febc3ca..47cdf3fbecef 100644
> --- a/include/linux/lsm_hooks.h
> +++ b/include/linux/lsm_hooks.h
> @@ -1595,7 +1595,7 @@ struct security_hook_list {
>   	struct hlist_node		list;
>   	struct hlist_head		*head;
>   	union security_list_options	hook;
> -	char				*lsm;
> +	const char			*lsm;
>   } __randomize_layout;
>   
>   /*
> @@ -1630,7 +1630,7 @@ extern struct security_hook_heads security_hook_heads;
>   extern char *lsm_names;
>   
>   extern void security_add_hooks(struct security_hook_list *hooks, int count,
> -				char *lsm);
> +				const char *lsm);
>   
>   #define LSM_FLAG_LEGACY_MAJOR	BIT(0)
>   #define LSM_FLAG_EXCLUSIVE	BIT(1)
> diff --git a/security/security.c b/security/security.c
> index 9663ffcca4b0..a48eb3badfdd 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -478,7 +478,7 @@ static int lsm_append(const char *new, char **result)
>    * Each LSM has to register its hooks with the infrastructure.
>    */
>   void __init security_add_hooks(struct security_hook_list *hooks, int count,
> -				char *lsm)
> +				const char *lsm)
>   {
>   	int i;
>