On Tue, Dec 2, 2025 at 6:20 AM Shuran Liu <[email protected]> wrote: > > Add a regression test for bpf_d_path() when invoked from an LSM program. > The test attaches to the bprm_check_security hook, calls bpf_d_path() on > the binary being executed, and verifies that a simple prefix comparison on > the returned pathname behaves correctly after the fix in patch 1.
I don't get why we add this selftest here. It doesn't appear to be related to patch 1/2. > > To avoid nondeterminism, the LSM program now filters based on the > expected PID, which is populated from userspace before the test binary is > executed. This prevents unrelated processes that also trigger the > bprm_check_security LSM hook from overwriting test results. Parent and > child processes are synchronized through a pipe to ensure the PID is set > before the child execs the test binary. The paragraph above is not really necessary. Just curious, did some AI write it? > > Per review feedback, the new LSM coverage is merged into the existing > d_path selftest rather than adding new prog_tests/ or progs/ files. The > loop that checks the pathname prefix now uses bpf_for(), which is a > verifier-friendly way to express a small, fixed-iteration loop, and the > temporary /tmp/bpf_d_path_test binary is removed in the test cleanup > path. > > Co-developed-by: Zesen Liu <[email protected]> > Signed-off-by: Zesen Liu <[email protected]> > Co-developed-by: Peili Gao <[email protected]> > Signed-off-by: Peili Gao <[email protected]> > Co-developed-by: Haoran Ni <[email protected]> > Signed-off-by: Haoran Ni <[email protected]> > Signed-off-by: Shuran Liu <[email protected]> > Reviewed-by: Matt Bobrowski <[email protected]> > --- > .../testing/selftests/bpf/prog_tests/d_path.c | 65 +++++++++++++++++++ > .../testing/selftests/bpf/progs/test_d_path.c | 33 ++++++++++ > 2 files changed, 98 insertions(+) > > diff --git a/tools/testing/selftests/bpf/prog_tests/d_path.c > b/tools/testing/selftests/bpf/prog_tests/d_path.c > index ccc768592e66..202b44e6f482 100644 > --- a/tools/testing/selftests/bpf/prog_tests/d_path.c > +++ b/tools/testing/selftests/bpf/prog_tests/d_path.c > @@ -195,6 +195,68 @@ static void test_d_path_check_types(void) > test_d_path_check_types__destroy(skel); > } > > +static void test_d_path_lsm(void) > +{ > + struct test_d_path *skel; > + int err; > + int pipefd[2]; > + pid_t pid; > + > + skel = test_d_path__open_and_load(); > + if (!ASSERT_OK_PTR(skel, "d_path skeleton failed")) > + return; > + > + err = test_d_path__attach(skel); > + if (!ASSERT_OK(err, "attach failed")) > + goto cleanup; > + > + /* Prepare the test binary */ > + system("cp /bin/true /tmp/bpf_d_path_test 2>/dev/null || :"); > + > + if (!ASSERT_OK(pipe(pipefd), "pipe failed")) > + goto cleanup; > + > + pid = fork(); > + if (!ASSERT_GE(pid, 0, "fork failed")) { > + close(pipefd[0]); > + close(pipefd[1]); > + goto cleanup; > + } > + > + if (pid == 0) { > + /* Child */ > + char buf; > + > + close(pipefd[1]); > + /* Wait for parent to set PID in BPF map */ > + if (read(pipefd[0], &buf, 1) != 1) > + exit(1); > + close(pipefd[0]); > + execl("/tmp/bpf_d_path_test", "/tmp/bpf_d_path_test", NULL); > + exit(1); > + } > + > + /* Parent */ > + close(pipefd[0]); > + > + /* Update BPF map with child PID */ > + skel->bss->my_pid = pid; > + > + /* Signal child to proceed */ > + write(pipefd[1], "G", 1); > + close(pipefd[1]); > + > + /* Wait for child */ > + waitpid(pid, NULL, 0); > + > + ASSERT_EQ(skel->bss->called_lsm, 1, "lsm hook called"); > + ASSERT_EQ(skel->bss->lsm_match, 1, "lsm match"); > + > +cleanup: > + unlink("/tmp/bpf_d_path_test"); > + test_d_path__destroy(skel); > +} > + > void test_d_path(void) > { > if (test__start_subtest("basic")) > @@ -205,4 +267,7 @@ void test_d_path(void) > > if (test__start_subtest("check_alloc_mem")) > test_d_path_check_types(); > + > + if (test__start_subtest("lsm")) > + test_d_path_lsm(); > } > diff --git a/tools/testing/selftests/bpf/progs/test_d_path.c > b/tools/testing/selftests/bpf/progs/test_d_path.c > index 84e1f883f97b..9ae36eabcd07 100644 > --- a/tools/testing/selftests/bpf/progs/test_d_path.c > +++ b/tools/testing/selftests/bpf/progs/test_d_path.c > @@ -17,6 +17,8 @@ int rets_close[MAX_FILES] = {}; > > int called_stat = 0; > int called_close = 0; > +int called_lsm = 0; > +int lsm_match = 0; > > SEC("fentry/security_inode_getattr") > int BPF_PROG(prog_stat, struct path *path, struct kstat *stat, > @@ -62,4 +64,35 @@ int BPF_PROG(prog_close, struct file *file, void *id) > return 0; > } > > +SEC("lsm/bprm_check_security") > +int BPF_PROG(prog_lsm, struct linux_binprm *bprm) > +{ > + pid_t pid = bpf_get_current_pid_tgid() >> 32; > + char path[MAX_PATH_LEN] = {}; > + int ret; > + > + if (pid != my_pid) > + return 0; > + > + called_lsm = 1; > + ret = bpf_d_path(&bprm->file->f_path, path, MAX_PATH_LEN); > + if (ret < 0) > + return 0; > + > + { This {} block is not necessary. > + static const char target_dir[] = "/tmp/"; > + int i; > + > + bpf_for(i, 0, sizeof(target_dir) - 1) { > + if (path[i] != target_dir[i]) { > + lsm_match = -1; /* mismatch */ > + return 0; > + } > + } > + } > + > + lsm_match = 1; /* prefix match */ > + return 0; > +} > + > char _license[] SEC("license") = "GPL"; > -- > 2.52.0 >
