From: Mickaël Salaün <mic@xxxxxxxxxxxxxxxxxxx> Add a new flag LANDLOCK_CREATE_RULESET_VERSION to landlock_create_ruleset(2). This enables to retreive a Landlock ABI version that is useful to efficiently follow a best-effort security approach. Indeed, it would be a missed opportunity to abort the whole sandbox building, because some features are unavailable, instead of protecting users as much as possible with the subset of features provided by the running kernel. This new flag enables user space to identify the minimum set of Landlock features supported by the running kernel without relying on a filesystem interface (e.g. /proc/version, which might be inaccessible) nor testing multiple syscall argument combinations (i.e. syscall bisection). New Landlock features will be documented and tied to a minimum version number (greater than 1). The current version will be incremented for each new kernel release supporting new Landlock features. User space libraries can leverage this information to seamlessly restrict processes as much as possible while being compatible with newer APIs. This is a much more lighter approach than the previous landlock_get_features(2): the complexity is pushed to user space libraries. This flag meets similar needs as securityfs versions: selinux/policyvers, apparmor/features/*/version* and tomoyo/version. Supporting this flag now will be convenient for backward compatibility. Cc: Arnd Bergmann <arnd@xxxxxxxx> Cc: James Morris <jmorris@xxxxxxxxx> Cc: Jann Horn <jannh@xxxxxxxxxx> Cc: Kees Cook <keescook@xxxxxxxxxxxx> Cc: Serge E. Hallyn <serge@xxxxxxxxxx> Signed-off-by: Mickaël Salaün <mic@xxxxxxxxxxxxxxxxxxx> Link: https://lore.kernel.org/r/20210422154123.13086-14-mic@xxxxxxxxxxx --- include/uapi/linux/landlock.h | 8 ++++ security/landlock/syscalls.c | 17 +++++-- tools/testing/selftests/landlock/base_test.c | 47 ++++++++++++++++++++ 3 files changed, 68 insertions(+), 4 deletions(-) diff --git a/include/uapi/linux/landlock.h b/include/uapi/linux/landlock.h index ba946a1e40b2..b3d952067f59 100644 --- a/include/uapi/linux/landlock.h +++ b/include/uapi/linux/landlock.h @@ -27,6 +27,14 @@ struct landlock_ruleset_attr { __u64 handled_access_fs; }; +/* + * sys_landlock_create_ruleset() flags: + * + * - %LANDLOCK_CREATE_RULESET_VERSION: Get the highest supported Landlock ABI + * version. + */ +#define LANDLOCK_CREATE_RULESET_VERSION (1U << 0) + /** * enum landlock_rule_type - Landlock rule type * diff --git a/security/landlock/syscalls.c b/security/landlock/syscalls.c index 93620ad7593b..32396962f04d 100644 --- a/security/landlock/syscalls.c +++ b/security/landlock/syscalls.c @@ -128,6 +128,8 @@ static const struct file_operations ruleset_fops = { .write = fop_dummy_write, }; +#define LANDLOCK_ABI_VERSION 1 + /** * sys_landlock_create_ruleset - Create a new ruleset * @@ -135,15 +137,19 @@ static const struct file_operations ruleset_fops = { * the new ruleset. * @size: Size of the pointed &struct landlock_ruleset_attr (needed for * backward and forward compatibility). - * @flags: Must be 0. + * @flags: Supported value: %LANDLOCK_CREATE_RULESET_VERSION. * * This system call enables to create a new Landlock ruleset, and returns the * related file descriptor on success. * + * If @flags is %LANDLOCK_CREATE_RULESET_VERSION and @attr is NULL and @size is + * 0, then the returned value is the highest supported Landlock ABI version + * (starting at 1). + * * Possible returned errors are: * * - EOPNOTSUPP: Landlock is supported by the kernel but disabled at boot time; - * - EINVAL: @flags is not 0, or unknown access, or too small @size; + * - EINVAL: unknown @flags, or unknown access, or too small @size; * - E2BIG or EFAULT: @attr or @size inconsistencies; * - ENOMSG: empty &landlock_ruleset_attr.handled_access_fs. */ @@ -161,9 +167,12 @@ SYSCALL_DEFINE3(landlock_create_ruleset, if (!landlock_initialized) return -EOPNOTSUPP; - /* No flag for now. */ - if (flags) + if (flags) { + if ((flags == LANDLOCK_CREATE_RULESET_VERSION) + && !attr && !size) + return LANDLOCK_ABI_VERSION; return -EINVAL; + } /* Copies raw user space buffer. */ err = copy_min_struct_from_user(&ruleset_attr, sizeof(ruleset_attr), diff --git a/tools/testing/selftests/landlock/base_test.c b/tools/testing/selftests/landlock/base_test.c index 262c3c8d953a..ca40abe9daa8 100644 --- a/tools/testing/selftests/landlock/base_test.c +++ b/tools/testing/selftests/landlock/base_test.c @@ -63,6 +63,53 @@ TEST(inconsistent_attr) { free(buf); } +TEST(abi_version) { + const struct landlock_ruleset_attr ruleset_attr = { + .handled_access_fs = LANDLOCK_ACCESS_FS_READ_FILE, + }; + ASSERT_EQ(1, landlock_create_ruleset(NULL, 0, + LANDLOCK_CREATE_RULESET_VERSION)); + + ASSERT_EQ(-1, landlock_create_ruleset(&ruleset_attr, 0, + LANDLOCK_CREATE_RULESET_VERSION)); + ASSERT_EQ(EINVAL, errno); + + ASSERT_EQ(-1, landlock_create_ruleset(NULL, sizeof(ruleset_attr), + LANDLOCK_CREATE_RULESET_VERSION)); + ASSERT_EQ(EINVAL, errno); + + ASSERT_EQ(-1, landlock_create_ruleset(&ruleset_attr, + sizeof(ruleset_attr), + LANDLOCK_CREATE_RULESET_VERSION)); + ASSERT_EQ(EINVAL, errno); + + ASSERT_EQ(-1, landlock_create_ruleset(NULL, 0, + LANDLOCK_CREATE_RULESET_VERSION | 1 << 31)); + ASSERT_EQ(EINVAL, errno); +} + +TEST(inval_create_ruleset_flags) { + const int last_flag = LANDLOCK_CREATE_RULESET_VERSION; + const int invalid_flag = last_flag << 1; + const struct landlock_ruleset_attr ruleset_attr = { + .handled_access_fs = LANDLOCK_ACCESS_FS_READ_FILE, + }; + + ASSERT_EQ(-1, landlock_create_ruleset(NULL, 0, invalid_flag)); + ASSERT_EQ(EINVAL, errno); + + ASSERT_EQ(-1, landlock_create_ruleset(&ruleset_attr, 0, invalid_flag)); + ASSERT_EQ(EINVAL, errno); + + ASSERT_EQ(-1, landlock_create_ruleset(NULL, sizeof(ruleset_attr), + invalid_flag)); + ASSERT_EQ(EINVAL, errno); + + ASSERT_EQ(-1, landlock_create_ruleset(&ruleset_attr, + sizeof(ruleset_attr), invalid_flag)); + ASSERT_EQ(EINVAL, errno); +} + TEST(empty_path_beneath_attr) { const struct landlock_ruleset_attr ruleset_attr = { .handled_access_fs = LANDLOCK_ACCESS_FS_EXECUTE, -- 2.31.1
