Re: [PATCH v1 2/7] landlock: Fix landlock_add_rule(2) signature

["Alejandro Colomar (man-pages)" <alx.manpages@gmail.com>]

Hi Mickaël,

On 21/2/22 16:53, Mickaël Salaün wrote:
> From: Mickaël Salaün <mic@linux.microsoft.com>
> 
> Replace the enum landlock_rule_type with an int in the syscall signature
> of landlock_add_rule to avoid an implementation-defined size.  In
> practice an enum type is like an int (at least with GCC and clang), but
> compilers may accept options (e.g. -fshort-enums) that would have an
> impact on that [1].  This change is mostly a cosmetic fix according to
> the current kernel compilers and used options.

There are two proposals for C2x that might bring C++ syntax to C for 
enums, i.e., being able to specify the underlying type of an enum.

See:
<http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2904.htm>
<http://www.open-std.org/jtc1/sc22/wg14/www/docs/n2908.htm>

Since the current kernel is safe from that enum problem, it may be 
better to wait and see what the standard decides to do with enum.  I 
guess they'll add this feature sooner or later.

Regards,
Alex

> 
> Link: https://lore.kernel.org/r/8a22a3c2-468c-e96c-6516-22a0f029aa34@gmail.com/ [1]
> Reported-by: Alejandro Colomar <alx.manpages@gmail.com>
> Cc: Nathan Chancellor <nathan@kernel.org>
> Cc: Nick Desaulniers <ndesaulniers@google.com>
> Signed-off-by: Mickaël Salaün <mic@linux.microsoft.com>
> Link: https://lore.kernel.org/r/20220221155311.166278-3-mic@digikod.net
> ---
>   include/linux/syscalls.h     | 3 +--
>   security/landlock/syscalls.c | 7 ++++---
>   2 files changed, 5 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
> index 819c0cb00b6d..a5956f91caf2 100644
> --- a/include/linux/syscalls.h
> +++ b/include/linux/syscalls.h
> @@ -71,7 +71,6 @@ struct clone_args;
>   struct open_how;
>   struct mount_attr;
>   struct landlock_ruleset_attr;
> -enum landlock_rule_type;
>   
>   #include <linux/types.h>
>   #include <linux/aio_abi.h>
> @@ -1053,7 +1052,7 @@ asmlinkage long sys_pidfd_send_signal(int pidfd, int sig,
>   asmlinkage long sys_pidfd_getfd(int pidfd, int fd, unsigned int flags);
>   asmlinkage long sys_landlock_create_ruleset(const struct landlock_ruleset_attr __user *attr,
>   		size_t size, __u32 flags);
> -asmlinkage long sys_landlock_add_rule(int ruleset_fd, enum landlock_rule_type rule_type,
> +asmlinkage long sys_landlock_add_rule(int ruleset_fd, int rule_type,
>   		const void __user *rule_attr, __u32 flags);
>   asmlinkage long sys_landlock_restrict_self(int ruleset_fd, __u32 flags);
>   asmlinkage long sys_memfd_secret(unsigned int flags);
> diff --git a/security/landlock/syscalls.c b/security/landlock/syscalls.c
> index fd4b24022a06..3b40fc5d0216 100644
> --- a/security/landlock/syscalls.c
> +++ b/security/landlock/syscalls.c
> @@ -277,8 +277,9 @@ static int get_path_from_fd(const s32 fd, struct path *const path)
>    *
>    * @ruleset_fd: File descriptor tied to the ruleset that should be extended
>    *		with the new rule.
> - * @rule_type: Identify the structure type pointed to by @rule_attr (only
> - *             LANDLOCK_RULE_PATH_BENEATH for now).
> + * @rule_type: Identify the structure type pointed to by @rule_attr as defined
> + *             by enum landlock_rule_type (only LANDLOCK_RULE_PATH_BENEATH for
> + *             now).
>    * @rule_attr: Pointer to a rule (only of type &struct
>    *             landlock_path_beneath_attr for now).
>    * @flags: Must be 0.
> @@ -301,7 +302,7 @@ static int get_path_from_fd(const s32 fd, struct path *const path)
>    * - EFAULT: @rule_attr inconsistency.
>    */
>   SYSCALL_DEFINE4(landlock_add_rule,
> -		const int, ruleset_fd, const enum landlock_rule_type, rule_type,
> +		const int, ruleset_fd, const int, rule_type,
>   		const void __user *const, rule_attr, const __u32, flags)
>   {
>   	struct landlock_path_beneath_attr path_beneath_attr;