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

["Mickaël Salaün" <mic@digikod.net>]

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@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.

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@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;
>