Filesystem denial traces identify the policy change needed to allow a request, so require exact blocker values rather than merely nonempty output. Pin a READ_DIR denial to exactly one event with blockers=read_dir. Pin a REFER-only mount denial to EPERM and exactly one event with blockers=change_topology.
The mount child retains CAP_SYS_ADMIN so Landlock is the only expected source of EPERM. This prevents a later capability failure from masking a Landlock regression; the trace-collecting parent remains unsandboxed. Cc: Günther Noack <[email protected]> Cc: Steven Rostedt <[email protected]> Signed-off-by: Mickaël Salaün <[email protected]> --- .../selftests/landlock/trace_fs_test.c | 76 ++++++++++++++++++- 1 file changed, 73 insertions(+), 3 deletions(-) diff --git a/tools/testing/selftests/landlock/trace_fs_test.c b/tools/testing/selftests/landlock/trace_fs_test.c index 6666d4746cb1..64014ade3a0e 100644 --- a/tools/testing/selftests/landlock/trace_fs_test.c +++ b/tools/testing/selftests/landlock/trace_fs_test.c @@ -548,7 +548,8 @@ TEST_F(trace_fs, check_rule_nested) */ TEST_F(trace_fs, deny_access_fs_denied) { - char *buf; + const char *const event_regex = REGEX_DENY_ACCESS_FS(TRACE_TASK); + char *buf, blockers[64]; int count; ASSERT_EQ(0, tracefs_clear_buf()); @@ -564,8 +565,77 @@ TEST_F(trace_fs, deny_access_fs_denied) buf = tracefs_read_buf(); ASSERT_NE(NULL, buf); - count = tracefs_count_matches(buf, REGEX_DENY_ACCESS_FS(TRACE_TASK)); - EXPECT_LE(1, count); + count = tracefs_count_matches(buf, event_regex); + EXPECT_EQ(1, count) + { + TH_LOG("Expected 1 access denial, got %d\n%s", count, buf); + } + ASSERT_EQ(0, tracefs_extract_field(buf, event_regex, "blockers", + blockers, sizeof(blockers))); + EXPECT_STREQ("read_dir", blockers); + + free(buf); +} + +/* + * Verifies that a denied mount reports the singleton topology blocker rather + * than an empty access mask. + */ +TEST_F(trace_fs, deny_change_topology) +{ + const char *const event_regex = REGEX_DENY_ACCESS_FS(TRACE_TASK); + const struct landlock_ruleset_attr ruleset_attr = { + .handled_access_fs = LANDLOCK_ACCESS_FS_REFER, + }; + char *buf, blockers[64]; + int count, ruleset_fd, status; + pid_t pid; + + ruleset_fd = + landlock_create_ruleset(&ruleset_attr, sizeof(ruleset_attr), 0); + ASSERT_LE(0, ruleset_fd); + ASSERT_EQ(0, tracefs_clear_buf()); + + /* Ensure that Landlock is the only expected mount denial. */ + set_cap(_metadata, CAP_SYS_ADMIN); + pid = fork(); + ASSERT_LE(0, pid); + if (pid == 0) { + if (prctl(PR_SET_NO_NEW_PRIVS, 1, 0, 0, 0)) { + close(ruleset_fd); + _exit(1); + } + if (landlock_restrict_self(ruleset_fd, 0)) { + close(ruleset_fd); + _exit(2); + } + close(ruleset_fd); + + if (mount(NULL, "/", NULL, MS_PRIVATE | MS_REC, NULL) != -1) + _exit(3); + + if (errno != EPERM) + _exit(4); + + _exit(0); + } + close(ruleset_fd); + clear_cap(_metadata, CAP_SYS_ADMIN); + + ASSERT_EQ(pid, waitpid(pid, &status, 0)); + ASSERT_TRUE(WIFEXITED(status)); + EXPECT_EQ(0, WEXITSTATUS(status)); + + buf = tracefs_read_buf(); + ASSERT_NE(NULL, buf); + count = tracefs_count_matches(buf, event_regex); + EXPECT_EQ(1, count) + { + TH_LOG("Expected 1 topology denial, got %d\n%s", count, buf); + } + ASSERT_EQ(0, tracefs_extract_field(buf, event_regex, "blockers", + blockers, sizeof(blockers))); + EXPECT_STREQ("change_topology", blockers); free(buf); } -- 2.55.0
