[PATCH v2] landlock: Improve bit operations in audit code

[Günther Noack]

On Mon, May 12, 2025 at 11:37:30AM +0200, Mickaël Salaün wrote:
> Use the BIT() and BIT_ULL() macros in the new audit code instead of
> explicit shifts to improve readability.  Use bitmask instead of modulo
> operation to simplify code.
> 
> Add test_range1_rand15() and test_range2_rand15() KUnit tests to improve
> get_id_range() coverage.
> 
> Signed-off-by: Günther Noack <gnoack3000 at gmail.com>
> Signed-off-by: Mickaël Salaün <mic at digikod.net>
> ---
> 
> Changes since v1:
> https://lore.kernel.org/r/20250507185404.1029055-1-mic@digikod.net
> - Use bitmask instead of modulo operation to simplify random value
>   truncation, suggested by Günther.
> - Add KUnit tests.
> ---
>  security/landlock/audit.c    |  2 +-
>  security/landlock/id.c       | 33 +++++++++++++++++++++++++++++++--
>  security/landlock/syscalls.c |  3 ++-
>  3 files changed, 34 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..56f7cc0fc744 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 &= 0b1111;
>  	step = number_of_ids + random_4bits;
>  
>  	/* It is safe to cast a signed atomic to an unsigned value. */
> @@ -144,6 +145,19 @@ static void test_range1_rand1(struct kunit *const test)
>  		init + 2);
>  }
>  
> +static void test_range1_rand15(struct kunit *const test)
> +{
> +	atomic64_t counter;
> +	u64 init;
> +
> +	init = get_random_u32();
> +	atomic64_set(&counter, init);
> +	KUNIT_EXPECT_EQ(test, get_id_range(1, &counter, 15), init);
> +	KUNIT_EXPECT_EQ(
> +		test, get_id_range(get_random_u8(), &counter, get_random_u8()),
> +		init + 16);
> +}
> +
>  static void test_range1_rand16(struct kunit *const test)
>  {
>  	atomic64_t counter;
> @@ -196,6 +210,19 @@ static void test_range2_rand2(struct kunit *const test)
>  		init + 4);
>  }
>  
> +static void test_range2_rand15(struct kunit *const test)
> +{
> +	atomic64_t counter;
> +	u64 init;
> +
> +	init = get_random_u32();
> +	atomic64_set(&counter, init);
> +	KUNIT_EXPECT_EQ(test, get_id_range(2, &counter, 15), init);
> +	KUNIT_EXPECT_EQ(
> +		test, get_id_range(get_random_u8(), &counter, get_random_u8()),
> +		init + 17);
> +}
> +
>  static void test_range2_rand16(struct kunit *const test)
>  {
>  	atomic64_t counter;
> @@ -232,10 +259,12 @@ static struct kunit_case __refdata test_cases[] = {
>  	KUNIT_CASE(test_init_once),
>  	KUNIT_CASE(test_range1_rand0),
>  	KUNIT_CASE(test_range1_rand1),
> +	KUNIT_CASE(test_range1_rand15),
>  	KUNIT_CASE(test_range1_rand16),
>  	KUNIT_CASE(test_range2_rand0),
>  	KUNIT_CASE(test_range2_rand1),
>  	KUNIT_CASE(test_range2_rand2),
> +	KUNIT_CASE(test_range2_rand15),
>  	KUNIT_CASE(test_range2_rand16),
>  	{}
>  	/* clang-format on */
> 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 <gnoack at google.com>