| lists.openwall.net | lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC | |
|
Open Source and information security mailing list archives
| ||
|
Message-ID: <aS7Ep6980hOjICSF@google.com>
Date: Tue, 2 Dec 2025 10:51:19 +0000
From: Matt Bobrowski <mattbobrowski@...gle.com>
To: Shuran Liu <electronlsr@...il.com>, g@...gle.com
Cc: song@...nel.org, bpf@...r.kernel.org, ast@...nel.org,
daniel@...earbox.net, andrii@...nel.org, martin.lau@...ux.dev,
eddyz87@...il.com, yonghong.song@...ux.dev,
john.fastabend@...il.com, kpsingh@...nel.org, sdf@...ichev.me,
haoluo@...gle.com, jolsa@...nel.org, rostedt@...dmis.org,
mhiramat@...nel.org, mathieu.desnoyers@...icios.com,
linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
Zesen Liu <ftyg@...e.com>, Peili Gao <gplhust955@...il.com>,
Haoran Ni <haoran.ni.cs@...il.com>
Subject: Re: [PATCH bpf v2 2/2] selftests/bpf: fix and consolidate d_path LSM
regression test
On Tue, Dec 02, 2025 at 05:30:15PM +0800, Shuran Liu wrote:
> Hi Matt,
>
> Thanks a lot for the review and for re-sending your Reviewed-by tag.
>
> In the next version of the series I’ll add your
>
> Reviewed-by: Matt Bobrowski <mattbobrowski@...gle.com>
>
> to the patch that introduces the new selftest, and I’ll also make sure to
> remove /tmp/bpf_d_path_test in the test cleanup path as you suggested.
SGTM.
> I also noticed that the CI is currently failing due to the `#pragma unroll`
> around the loop in prog_lsm(). Would you prefer that I simply drop the pragma
> in the next version, given that the loop bound is small and constant anyway,
> or is there a better way you’d recommend to handle this?
Yeah, I don't think the use of this directive is required here given
the iteration count is tiny. Alternatively, perhaps you could switch
over to using a more BPF verifier preferred alternative
(i.e. bpf_for() or better yet and simpler bpf_repeat())?
> > On Tue, Dec 02, 2025 at 00:59:45AM -0800, Matt Bobrowski wrote：
> >
> > On Tue, Dec 02, 2025 at 03:54:41PM +0800, Shuran Liu 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.
> >>
> >> 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.
> >>
> >> Per review feedback, the new test is merged into the existing d_path
> >> selftest rather than adding new prog_tests/ or progs/ files.
> >>
> >> Co-developed-by: Zesen Liu <ftyg@...e.com>
> >> Signed-off-by: Zesen Liu <ftyg@...e.com>
> >> Co-developed-by: Peili Gao <gplhust955@...il.com>
> >> Signed-off-by: Peili Gao <gplhust955@...il.com>
> >> Co-developed-by: Haoran Ni <haoran.ni.cs@...il.com>
> >> Signed-off-by: Haoran Ni <haoran.ni.cs@...il.com>
> >> Signed-off-by: Shuran Liu <electronlsr@...il.com>
> >
> > Feel free to add:
> >
> > Reviewed-by: Matt Bobrowski <mattbobrowski@...gle.com <mailto:mattbobrowski@...gle.com>>
> >
> >> ---
> >> .../testing/selftests/bpf/prog_tests/d_path.c | 64 +++++++++++++++++++
> >> .../testing/selftests/bpf/progs/test_d_path.c | 33 ++++++++++
> >> 2 files changed, 97 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..2909ca3bae0f 100644
> >> --- a/tools/testing/selftests/bpf/prog_tests/d_path.c
> >> +++ b/tools/testing/selftests/bpf/prog_tests/d_path.c
> >> @@ -195,6 +195,67 @@ 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 || :");
> >
> > I'd much prefer if we also cleaned up after ourselves, but it's not
> > that much of an issue I guess.
> >
> >> + 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:
> >> + test_d_path__destroy(skel);
> >> +}
> >> +
> >> void test_d_path(void)
> >> {
> >> if (test__start_subtest("basic"))
> >> @@ -205,4 +266,7 @@ 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..7f65c282069a 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;
> >> +
> >> + {
> >> + static const char target_dir[] = "/tmp/";
> >> +
> >> +#pragma unroll
> >> + for (int i = 0; i < sizeof(target_dir) - 1; i++) {
> >> + 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
>
Powered by blists - more mailing lists