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

[Mickaël Salaün <mic@xxxxxxxxxxx>]

On 26/02/2022 22:26, Alejandro Colomar (man-pages) wrote:
> Hi Mickaël,
>
> On 21/2/22 16:53, Mickaël Salaün wrote:
> > From: Mickaël Salaün <mic@xxxxxxxxxxxxxxxxxxx>
> >
> > 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.

Ok, interesting, I'll remove this patch then. I'd be curious to know 
when this will impact Linux though.

Thanks!

> Regards,
> Alex
>
> > Link: 
> > https://lore.kernel.org/r/8a22a3c2-468c-e96c-6516-22a0f029aa34@xxxxxxxxx/ 
> > [1]
> > Reported-by: Alejandro Colomar <alx.manpages@xxxxxxxxx>
> > Cc: Nathan Chancellor <nathan@xxxxxxxxxx>
> > Cc: Nick Desaulniers <ndesaulniers@xxxxxxxxxx>
> > Signed-off-by: Mickaël Salaün <mic@xxxxxxxxxxxxxxxxxxx>
> > Link: https://lore.kernel.org/r/20220221155311.166278-3-mic@xxxxxxxxxxx
> > ---
> >   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;