[PATCH v1] landlock: Use bitops macros in audit code

[Günther Noack]

On Wed, May 07, 2025 at 08:54:02PM +0200, Mickaël Salaün wrote:
> Use the BIT() and BIT_ULL() macros in the new audit code instead of
> explicit shifts to improve readability.
> 
> Cc: Günther Noack <gnoack at google.com>
> Signed-off-by: Mickaël Salaün <mic at digikod.net>
> ---
>  security/landlock/audit.c    | 2 +-
>  security/landlock/id.c       | 5 +++--
>  security/landlock/syscalls.c | 3 ++-
>  3 files changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/security/landlock/audit.c b/security/landlock/audit.c
> index 58d5c40d4d0e..c52d079cdb77 100644
> --- a/security/landlock/audit.c
> +++ b/security/landlock/audit.c
> @@ -437,7 +437,7 @@ void landlock_log_denial(const struct landlock_cred_security *const subject,
>  		return;
>  
>  	/* Checks if the current exec was restricting itself. */
> -	if (subject->domain_exec & (1 << youngest_layer)) {
> +	if (subject->domain_exec & BIT(youngest_layer)) {
>  		/* Ignores denials for the same execution. */
>  		if (!youngest_denied->log_same_exec)
>  			return;
> diff --git a/security/landlock/id.c b/security/landlock/id.c
> index 11fab9259c15..552272307697 100644
> --- a/security/landlock/id.c
> +++ b/security/landlock/id.c
> @@ -7,6 +7,7 @@
>  
>  #include <kunit/test.h>
>  #include <linux/atomic.h>
> +#include <linux/bitops.h>
>  #include <linux/random.h>
>  #include <linux/spinlock.h>
>  
> @@ -25,7 +26,7 @@ static void __init init_id(atomic64_t *const counter, const u32 random_32bits)
>  	 * Ensures sure 64-bit values are always used by user space (or may
>  	 * fail with -EOVERFLOW), and makes this testable.
>  	 */
> -	init = 1ULL << 32;
> +	init = BIT_ULL(32);
>  
>  	/*
>  	 * Makes a large (2^32) boot-time value to limit ID collision in logs
> @@ -105,7 +106,7 @@ static u64 get_id_range(size_t number_of_ids, atomic64_t *const counter,
>  	 * to get a new ID (e.g. a full landlock_restrict_self() call), and the
>  	 * cost of draining all available IDs during the system's uptime.
>  	 */
> -	random_4bits = random_4bits % (1 << 4);
> +	random_4bits = random_4bits % BIT(4);

Optional nit: Might be slightly simpler when written as a bitwise AND:

  random_4bits = random_4bits & 0b1111;

(Probably does not make a difference in the compiled code though?)

And, to also simplify the statement:

  random_4bits &= 0b1111;

(If you prefer to stick with the modulo, "%=" exists as well, even
though it's more obscure.)

>  	step = number_of_ids + random_4bits;
>  
>  	/* It is safe to cast a signed atomic to an unsigned value. */
> diff --git a/security/landlock/syscalls.c b/security/landlock/syscalls.c
> index b9561e3417ae..33eafb71e4f3 100644
> --- a/security/landlock/syscalls.c
> +++ b/security/landlock/syscalls.c
> @@ -9,6 +9,7 @@
>  
>  #include <asm/current.h>
>  #include <linux/anon_inodes.h>
> +#include <linux/bitops.h>
>  #include <linux/build_bug.h>
>  #include <linux/capability.h>
>  #include <linux/cleanup.h>
> @@ -563,7 +564,7 @@ SYSCALL_DEFINE2(landlock_restrict_self, const int, ruleset_fd, const __u32,
>  	new_llcred->domain = new_dom;
>  
>  #ifdef CONFIG_AUDIT
> -	new_llcred->domain_exec |= 1 << (new_dom->num_layers - 1);
> +	new_llcred->domain_exec |= BIT(new_dom->num_layers - 1);
>  #endif /* CONFIG_AUDIT */
>  
>  	return commit_creds(new_cred);
> -- 
> 2.49.0
> 

Signed-off-by: Günther Noack <gnoack3000 at gmail.com>