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Hallyn" , linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org, =?iso-8859-1?q?Bj=F6rn?= Roy Baron , Jann Horn , outreachy@lists.linux.dev, netdev@vger.kernel.org Subject: [PATCH v4] landlock: Add abstract unix socket connect restriction Message-ID: Precedence: bulk X-Mailing-List: linux-security-module@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Disposition: inline Abstract unix sockets are used for local inter-process communications without on a filesystem. Currently a sandboxed process can connect to a socket outside of the sandboxed environment, since landlock has no restriction for connecting to a unix socket in the abstract namespace. Access to such sockets for a sandboxed process should be scoped the same way ptrace is limited. Because of compatibility reasons and since landlock should be flexible, we extend the user space interface by adding a new "scoped" field. This field optionally contains a "LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET" to specify that the ruleset will deny any connection from within the sandbox to its parents(i.e. any parent sandbox or non-sandbox processes) Closes: https://github.com/landlock-lsm/linux/issues/7 Signed-off-by: Tahera Fahimi ------- V3: Added "scoped" field to landlock_ruleset_attr V2: Remove wrapper functions ------- Signed-off-by: Tahera Fahimi --- include/uapi/linux/landlock.h | 27 ++ security/landlock/limits.h | 3 + security/landlock/ruleset.c | 7 +- security/landlock/ruleset.h | 29 +- security/landlock/syscalls.c | 13 +- security/landlock/task.c | 58 ++++ .../testing/selftests/landlock/ptrace_test.c | 261 ++++++++++++++++++ 7 files changed, 392 insertions(+), 6 deletions(-) diff --git a/include/uapi/linux/landlock.h b/include/uapi/linux/landlock.h index 68625e728f43..3ea370c52aaa 100644 --- a/include/uapi/linux/landlock.h +++ b/include/uapi/linux/landlock.h @@ -37,6 +37,11 @@ struct landlock_ruleset_attr { * rule explicitly allow them. */ __u64 handled_access_net; + /** + * scoped: Bitmask of actions (cf. `Scope access flags`_) + * which are confined to only affect the current Landlock domain. + */ + __u64 scoped; }; /* @@ -266,4 +271,26 @@ struct landlock_net_port_attr { #define LANDLOCK_ACCESS_NET_BIND_TCP (1ULL << 0) #define LANDLOCK_ACCESS_NET_CONNECT_TCP (1ULL << 1) /* clang-format on */ + +/** + * DOC: scope + * + * .scoped attribute handles a set of restrictions on kernel IPCs through + * the following flags. + * + * Scope access flags + * ~~~~~~~~~~~~~~~~~~~~ + * + * These flags enable to restrict a sandboxed process from a set of IPC + * actions. Setting a flag in a landlock domain will isolate the Landlock + * domain to forbid connections to resources outside the domain. + * + * IPCs with allowed actions: + * - %LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET: Restrict a sandbox process to + * connect to a process outside of the sandbox domain through abstract + * unix sockets. + */ +/* clang-format off */ +#define LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET (1ULL << 0) +/* clang-format on*/ #endif /* _UAPI_LINUX_LANDLOCK_H */ diff --git a/security/landlock/limits.h b/security/landlock/limits.h index 4eb643077a2a..93d5fa8495b2 100644 --- a/security/landlock/limits.h +++ b/security/landlock/limits.h @@ -26,6 +26,9 @@ #define LANDLOCK_MASK_ACCESS_NET ((LANDLOCK_LAST_ACCESS_NET << 1) - 1) #define LANDLOCK_NUM_ACCESS_NET __const_hweight64(LANDLOCK_MASK_ACCESS_NET) +#define LANDLOCK_LAST_ACCESS_SCOPE LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET +#define LANDLOCK_MASK_ACCESS_SCOPE ((LANDLOCK_LAST_ACCESS_SCOPE << 1) - 1) +#define LANDLOCK_NUM_ACCESS_SCOPE __const_hweight64(LANDLOCK_MASK_ACCESS_SCOPE) /* clang-format on */ #endif /* _SECURITY_LANDLOCK_LIMITS_H */ diff --git a/security/landlock/ruleset.c b/security/landlock/ruleset.c index 6ff232f58618..a93bdbf52fff 100644 --- a/security/landlock/ruleset.c +++ b/security/landlock/ruleset.c @@ -52,12 +52,13 @@ static struct landlock_ruleset *create_ruleset(const u32 num_layers) struct landlock_ruleset * landlock_create_ruleset(const access_mask_t fs_access_mask, - const access_mask_t net_access_mask) + const access_mask_t net_access_mask, + const access_mask_t scope_mask) { struct landlock_ruleset *new_ruleset; /* Informs about useless ruleset. */ - if (!fs_access_mask && !net_access_mask) + if (!fs_access_mask && !net_access_mask && !scope_mask) return ERR_PTR(-ENOMSG); new_ruleset = create_ruleset(1); if (IS_ERR(new_ruleset)) @@ -66,6 +67,8 @@ landlock_create_ruleset(const access_mask_t fs_access_mask, landlock_add_fs_access_mask(new_ruleset, fs_access_mask, 0); if (net_access_mask) landlock_add_net_access_mask(new_ruleset, net_access_mask, 0); + if (scope_mask) + landlock_add_scope_mask(new_ruleset, scope_mask, 0); return new_ruleset; } diff --git a/security/landlock/ruleset.h b/security/landlock/ruleset.h index 0f1b5b4c8f6b..2d3f41613bdc 100644 --- a/security/landlock/ruleset.h +++ b/security/landlock/ruleset.h @@ -35,6 +35,8 @@ typedef u16 access_mask_t; static_assert(BITS_PER_TYPE(access_mask_t) >= LANDLOCK_NUM_ACCESS_FS); /* Makes sure all network access rights can be stored. */ static_assert(BITS_PER_TYPE(access_mask_t) >= LANDLOCK_NUM_ACCESS_NET); +/* Makes sure all scoped rights can be stored*/ +static_assert(BITS_PER_TYPE(access_mask_t) >= LANDLOCK_NUM_ACCESS_SCOPE); /* Makes sure for_each_set_bit() and for_each_clear_bit() calls are OK. */ static_assert(sizeof(unsigned long) >= sizeof(access_mask_t)); @@ -42,8 +44,15 @@ static_assert(sizeof(unsigned long) >= sizeof(access_mask_t)); struct access_masks { access_mask_t fs : LANDLOCK_NUM_ACCESS_FS; access_mask_t net : LANDLOCK_NUM_ACCESS_NET; + access_mask_t scoped : LANDLOCK_NUM_ACCESS_SCOPE; }; +typedef u32 access_masks_t; +/* Makes sure all ruleset access rights can be stored. */ +static_assert(BITS_PER_TYPE(access_masks_t) >= + LANDLOCK_NUM_ACCESS_FS + LANDLOCK_NUM_ACCESS_NET + + LANDLOCK_NUM_ACCESS_SCOPE); + typedef u16 layer_mask_t; /* Makes sure all layers can be checked. */ static_assert(BITS_PER_TYPE(layer_mask_t) >= LANDLOCK_MAX_NUM_LAYERS); @@ -233,7 +242,8 @@ struct landlock_ruleset { struct landlock_ruleset * landlock_create_ruleset(const access_mask_t access_mask_fs, - const access_mask_t access_mask_net); + const access_mask_t access_mask_net, + const access_mask_t scope_mask); void landlock_put_ruleset(struct landlock_ruleset *const ruleset); void landlock_put_ruleset_deferred(struct landlock_ruleset *const ruleset); @@ -280,6 +290,16 @@ landlock_add_net_access_mask(struct landlock_ruleset *const ruleset, ruleset->access_masks[layer_level].net |= net_mask; } +static inline void +landlock_add_scope_mask(struct landlock_ruleset *const ruleset, + const access_mask_t scope_mask, const u16 layer_level) +{ + access_mask_t scoped_mask = scope_mask & LANDLOCK_MASK_ACCESS_SCOPE; + + WARN_ON_ONCE(scope_mask != scoped_mask); + ruleset->access_masks[layer_level].scoped |= scoped_mask; +} + static inline access_mask_t landlock_get_raw_fs_access_mask(const struct landlock_ruleset *const ruleset, const u16 layer_level) @@ -303,6 +323,13 @@ landlock_get_net_access_mask(const struct landlock_ruleset *const ruleset, return ruleset->access_masks[layer_level].net; } +static inline access_mask_t +landlock_get_scope_mask(const struct landlock_ruleset *const ruleset, + const u16 layer_level) +{ + return ruleset->access_masks[layer_level].scoped; +} + bool landlock_unmask_layers(const struct landlock_rule *const rule, const access_mask_t access_request, layer_mask_t (*const layer_masks)[], diff --git a/security/landlock/syscalls.c b/security/landlock/syscalls.c index 03b470f5a85a..15ad79ac022b 100644 --- a/security/landlock/syscalls.c +++ b/security/landlock/syscalls.c @@ -97,8 +97,9 @@ static void build_check_abi(void) */ ruleset_size = sizeof(ruleset_attr.handled_access_fs); ruleset_size += sizeof(ruleset_attr.handled_access_net); + ruleset_size += sizeof(ruleset_attr.scoped); BUILD_BUG_ON(sizeof(ruleset_attr) != ruleset_size); - BUILD_BUG_ON(sizeof(ruleset_attr) != 16); + BUILD_BUG_ON(sizeof(ruleset_attr) != 24); path_beneath_size = sizeof(path_beneath_attr.allowed_access); path_beneath_size += sizeof(path_beneath_attr.parent_fd); @@ -170,7 +171,7 @@ static const struct file_operations ruleset_fops = { * Possible returned errors are: * * - %EOPNOTSUPP: Landlock is supported by the kernel but disabled at boot time; - * - %EINVAL: unknown @flags, or unknown access, or too small @size; + * - %EINVAL: unknown @flags, or unknown access, or uknown scope, or too small @size; * - %E2BIG or %EFAULT: @attr or @size inconsistencies; * - %ENOMSG: empty &landlock_ruleset_attr.handled_access_fs. */ @@ -212,10 +213,16 @@ SYSCALL_DEFINE3(landlock_create_ruleset, if ((ruleset_attr.handled_access_net | LANDLOCK_MASK_ACCESS_NET) != LANDLOCK_MASK_ACCESS_NET) return -EINVAL; + + /* Checks IPC scoping content (and 32-bits cast). */ + if ((ruleset_attr.scoped | LANDLOCK_MASK_ACCESS_SCOPE) != + LANDLOCK_MASK_ACCESS_SCOPE) + return -EINVAL; /* Checks arguments and transforms to kernel struct. */ ruleset = landlock_create_ruleset(ruleset_attr.handled_access_fs, - ruleset_attr.handled_access_net); + ruleset_attr.handled_access_net, + ruleset_attr.scoped); if (IS_ERR(ruleset)) return PTR_ERR(ruleset); diff --git a/security/landlock/task.c b/security/landlock/task.c index 849f5123610b..b8bde74ff684 100644 --- a/security/landlock/task.c +++ b/security/landlock/task.c @@ -13,6 +13,8 @@ #include #include #include +#include +#include #include "common.h" #include "cred.h" @@ -108,9 +110,65 @@ static int hook_ptrace_traceme(struct task_struct *const parent) return task_ptrace(parent, current); } +static access_mask_t +get_scoped_accesses(const struct landlock_ruleset *const domain) +{ + access_mask_t access_dom = 0; + size_t layer_level; + + for (layer_level = 0; layer_level < domain->num_layers; layer_level++) + access_dom |= landlock_get_scope_mask(domain, layer_level); + return access_dom; +} + +static bool sock_is_scoped(struct sock *const other) +{ + bool is_scoped = true; + const struct landlock_ruleset *dom_other; + const struct landlock_ruleset *const dom = + landlock_get_current_domain(); + + /* quick return if there is no domain or .scoped is not set */ + if (!dom || !get_scoped_accesses(dom)) + return true; + + /* the credentials will not change */ + lockdep_assert_held(&unix_sk(other)->lock); + if (other->sk_type != SOCK_DGRAM){ + dom_other = landlock_cred(other->sk_peer_cred)->domain; + } else { + dom_other = landlock_cred(other->sk_socket->file->f_cred)->domain; + } + is_scoped = domain_scope_le(dom, dom_other); + return is_scoped; +} + +static int hook_unix_stream_connect(struct sock *const sock, + struct sock *const other, + struct sock *const newsk) +{ + if (sock_is_scoped(other)) + return 0; + + return -EPERM; +} + +static int hook_unix_may_send(struct socket *const sock, + struct socket *const other) +{ + pr_warn("XXX %s:%d sock->file:%p other->file:%p\n", __func__, __LINE__, + sock->file, other->file); + if (sock_is_scoped(other->sk)) + return 0; + + return -EPERM; +} + static struct security_hook_list landlock_hooks[] __ro_after_init = { LSM_HOOK_INIT(ptrace_access_check, hook_ptrace_access_check), LSM_HOOK_INIT(ptrace_traceme, hook_ptrace_traceme), + LSM_HOOK_INIT(unix_stream_connect, hook_unix_stream_connect), + LSM_HOOK_INIT(unix_may_send, hook_unix_may_send), }; __init void landlock_add_task_hooks(void) diff --git a/tools/testing/selftests/landlock/ptrace_test.c b/tools/testing/selftests/landlock/ptrace_test.c index a19db4d0b3bd..73eddf08907e 100644 --- a/tools/testing/selftests/landlock/ptrace_test.c +++ b/tools/testing/selftests/landlock/ptrace_test.c @@ -17,6 +17,10 @@ #include #include +#include +#include +#include + #include "common.h" /* Copied from security/yama/yama_lsm.c */ @@ -436,4 +440,261 @@ TEST_F(hierarchy, trace) _metadata->exit_code = KSFT_FAIL; } +static void create_unix_domain(struct __test_metadata *const _metadata) +{ + int ruleset_fd; + const struct landlock_ruleset_attr ruleset_attr = { + .scoped = LANDLOCK_SCOPED_ABSTRACT_UNIX_SOCKET, + }; + + ruleset_fd = + landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0); + EXPECT_LE(0, ruleset_fd) + { + TH_LOG("Failed to create a ruleset: %s", strerror(errno)); + } + enforce_ruleset(_metadata, ruleset_fd); + EXPECT_EQ(0, close(ruleset_fd)); +} + +/* clang-format off */ +FIXTURE(unix_socket) +{ + int server, client; +}; +/* clang-format on */ + +FIXTURE_VARIANT(unix_socket) +{ + int type; + bool domain_both; + bool domain_parent; + bool domain_child; + bool connect_to_parent; +}; + +/* clang-format off */ +FIXTURE_VARIANT_ADD(unix_socket, allow_without_domain) { + /* clang-format on */ + .type = SOCK_STREAM, .domain_both = false, + .domain_parent = false, .domain_child = false, + .connect_to_parent = true, +}; + +/* clang-format off */ +FIXTURE_VARIANT_ADD(unix_socket, deny_child_connection_with_domain) { + /* clang-format on */ + .type = SOCK_STREAM, .domain_both = false, .domain_parent = false, + .domain_child = true, .connect_to_parent = true, +}; + +/* clang-format off */ +FIXTURE_VARIANT_ADD(unix_socket, allow_child_connection_and_parent_domain) { + /* clang-format on */ + .type = SOCK_STREAM, .domain_both = false, .domain_parent = true, + .domain_child = false, .connect_to_parent = true, +}; + +/* clang-format off */ +FIXTURE_VARIANT_ADD(unix_socket, deny_parent_connection_with_domain) { + /* clang-format on */ + .type = SOCK_STREAM, .domain_both = false, + .domain_parent = true, .domain_child = false, + .connect_to_parent = false, +}; + +/* clang-format off */ +FIXTURE_VARIANT_ADD(unix_socket, allow_parent_connection_without_domain) { + /* clang-format on */ + .type = SOCK_STREAM, .domain_both = false, + .domain_parent = false, .domain_child = false, + .connect_to_parent = false, +}; + +/* clang-format off */ +FIXTURE_VARIANT_ADD(unix_socket, allow_parent_connection_with_sibling_domain) { + /* clang-format on */ + .type = SOCK_STREAM, .domain_both = true, + .domain_parent = false, .domain_child = false, + .connect_to_parent = false, +}; + +/* clang-format off */ +FIXTURE_VARIANT_ADD(unix_socket, dgrm_allow_without_domain) { + /* clang-format on */ + .type = SOCK_DGRAM, .domain_both = false, + .domain_parent = false, .domain_child = false, + .connect_to_parent = true, +}; + +/* clang-format off */ +FIXTURE_VARIANT_ADD(unix_socket, dgrm_deny_child_connection_with_domain) { + /* clang-format on */ + .type = SOCK_DGRAM, .domain_both = false, .domain_parent = false, + .domain_child = true, .connect_to_parent = true, +}; + +/* clang-format off */ +FIXTURE_VARIANT_ADD(unix_socket, dgrm_allow_child_with_sibling_domain) { + /* clang-format on */ + .type = SOCK_DGRAM, .domain_both = true, + .domain_parent = false, .domain_child = false, + .connect_to_parent = true, +}; + +/* clang-format off */ +FIXTURE_VARIANT_ADD(unix_socket, dgrm_deny_parent_connection_with_domain) { + /* clang-format on */ + .type = SOCK_DGRAM, .domain_both = false, + .domain_parent = true, .domain_child = false, + .connect_to_parent = false, +}; + +/* clang-format off */ +FIXTURE_VARIANT_ADD(unix_socket, dgrm_allow_parent_connection_with_child_domain) { + /* clang-format on */ + .type = SOCK_DGRAM, .domain_both = false, + .domain_parent = false, .domain_child = true, + .connect_to_parent = false, +}; + +FIXTURE_SETUP(unix_socket) +{ +} + +FIXTURE_TEARDOWN(unix_socket) +{ + close(self->server); + close(self->client); +} + +/* Test UNIX_STREAM_CONNECT for parent and child. */ +TEST_F(unix_socket, abstract_unix_socket) +{ + int status; + pid_t child; + socklen_t addrlen; + int sock_len = 5; + struct sockaddr_un addr = { + .sun_family = AF_UNIX, + }; + const char sun_path[8] = "\0test"; + bool can_connect_to_parent, can_connect_to_child; + int err; + int pipe_child[2], pipe_parent[2]; + char buf_parent; + /* + * can_connect_to_child is true if a parent process can connect to its + * child process. The parent process is not isolated from the child + * with a dedicated Landlock domain. + */ + can_connect_to_child = !variant->domain_parent; + /* + * can_connect_to_parent is true if a child process can connect to its parent + * process. This depends on the child process is not isolated from + * the parent with a dedicated Landlock domain. + */ + can_connect_to_parent = !variant->domain_child; + + ASSERT_EQ(0, pipe2(pipe_child, O_CLOEXEC)); + ASSERT_EQ(0, pipe2(pipe_parent, O_CLOEXEC)); + if (variant->domain_both) { + create_unix_domain(_metadata); + if (!__test_passed(_metadata)) + return; + } + + addrlen = offsetof(struct sockaddr_un, sun_path) + sock_len; + memcpy(&addr.sun_path, sun_path, sock_len); + + child = fork(); + ASSERT_LE(0, child); + if (child == 0) { + int child_ret; + char buf_child; + + ASSERT_EQ(0, close(pipe_parent[1])); + ASSERT_EQ(0, close(pipe_child[0])); + if (variant->domain_child) + create_unix_domain(_metadata); + + /* Waits for the parent to be in a domain, if any. */ + ASSERT_EQ(1, read(pipe_parent[0], &buf_child, 1)); + + /* create a socket for child process */ + if (variant->connect_to_parent) { + self->client = socket(AF_UNIX, variant->type, 0); + ASSERT_NE(-1, self->client); + + ASSERT_EQ(1, read(pipe_parent[0], &buf_child, 1)); + child_ret = connect(self->client, + (struct sockaddr *)&addr, addrlen); + if (can_connect_to_parent) { + EXPECT_EQ(0, child_ret); + } else { + EXPECT_EQ(-1, child_ret); + EXPECT_EQ(EPERM, errno); + } + } else { + /* child process should create a listening socket */ + self->server = socket(AF_UNIX, variant->type, 0); + ASSERT_NE(-1, self->server); + + ASSERT_EQ(0, bind(self->server, + (struct sockaddr *)&addr, addrlen)); + if (variant->type == SOCK_STREAM) { + err = listen(self->server, 32); + ASSERT_EQ(0, err); + } + /* signal to parent that child is listening */ + ASSERT_EQ(1, write(pipe_child[1], ".", 1)); + /* wait to connect */ + ASSERT_EQ(1, read(pipe_parent[0], &buf_child, 1)); + } + _exit(_metadata->exit_code); + return; + } + + ASSERT_EQ(0, close(pipe_child[1])); + ASSERT_EQ(0, close(pipe_parent[0])); + + if (variant->domain_parent) + create_unix_domain(_metadata); + + /* Signals that the parent is in a domain, if any. */ + ASSERT_EQ(1, write(pipe_parent[1], ".", 1)); + + if (!variant->connect_to_parent) { + self->client = socket(AF_UNIX, variant->type, 0); + ASSERT_NE(-1, self->client); + /* Waits for the child to listen */ + ASSERT_EQ(1, read(pipe_child[0], &buf_parent, 1)); + err = connect(self->client, (struct sockaddr *)&addr, addrlen); + if (can_connect_to_child) { + EXPECT_EQ(0, err); + } else { + EXPECT_EQ(-1, err); + EXPECT_EQ(EPERM, errno); + } + ASSERT_EQ(1, write(pipe_parent[1], ".", 1)); + } else { + self->server = socket(AF_UNIX, variant->type, 0); + ASSERT_NE(-1, self->server); + ASSERT_EQ(0, bind(self->server, (struct sockaddr *)&addr, + addrlen)); + if (variant->type == SOCK_STREAM) { + err = listen(self->server, 32); + ASSERT_EQ(0, err); + } + /* signal to child that parent is listening */ + ASSERT_EQ(1, write(pipe_parent[1], ".", 1)); + } + + ASSERT_EQ(child, waitpid(child, &status, 0)); + + if (WIFSIGNALED(status) || !WIFEXITED(status) || + WEXITSTATUS(status) != EXIT_SUCCESS) + _metadata->exit_code = KSFT_FAIL; +} + TEST_HARNESS_MAIN