Re: [PATCH bpf-next v5 7/7] bpf: lsm: Add selftests for BPF_PROG_TYPE_LSM

Yonghong Song
2020-03-23T20:05:17Z

On 3/23/20 9:44 AM, KP Singh wrote:
> From: KP Singh <kpsingh@google.com>
>
> * Load/attach a BPF program to the file_mprotect (int) and
> bprm_committed_creds (void) LSM hooks.
> * Perform an action that triggers the hook.
> * Verify if the audit event was received using a shared global
> result variable.
>
> Signed-off-by: KP Singh <kpsingh@google.com>
> Reviewed-by: Brendan Jackman <jackmanb@google.com>
> Reviewed-by: Florent Revest <revest@google.com>
> Reviewed-by: Thomas Garnier <thgarnie@google.com>
> ---
> tools/testing/selftests/bpf/lsm_helpers.h | 19 +++
> .../selftests/bpf/prog_tests/lsm_test.c | 112 ++++++++++++++++++
> .../selftests/bpf/progs/lsm_int_hook.c | 54 +++++++++
> .../selftests/bpf/progs/lsm_void_hook.c | 41 +++++++
> 4 files changed, 226 insertions(+)
> create mode 100644 tools/testing/selftests/bpf/lsm_helpers.h
> create mode 100644 tools/testing/selftests/bpf/prog_tests/lsm_test.c
> create mode 100644 tools/testing/selftests/bpf/progs/lsm_int_hook.c
> create mode 100644 tools/testing/selftests/bpf/progs/lsm_void_hook.c
>
> diff --git a/tools/testing/selftests/bpf/lsm_helpers.h b/tools/testing/selftests/bpf/lsm_helpers.h
> new file mode 100644
> index 000000000000..3de230df93db
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/lsm_helpers.h
> @@ -0,0 +1,19 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +/*
> + * Copyright (C) 2020 Google LLC.
> + */
> +#ifndef _LSM_HELPERS_H
> +#define _LSM_HELPERS_H
> +
> +struct lsm_prog_result {
> + /* This ensures that the LSM Hook only monitors the PID requested
> + * by the loader
> + */
> + __u32 monitored_pid;
> + /* The number of calls to the prog for the monitored PID.
> + */
> + __u32 count;
> +};
> +
> +#endif /* _LSM_HELPERS_H */
> diff --git a/tools/testing/selftests/bpf/prog_tests/lsm_test.c b/tools/testing/selftests/bpf/prog_tests/lsm_test.c
> new file mode 100644
> index 000000000000..5fd6b8f569f7
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/lsm_test.c
> @@ -0,0 +1,112 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +/*
> + * Copyright (C) 2020 Google LLC.
> + */
> +
> +#include <test_progs.h>
> +#include <sys/mman.h>
> +#include <sys/wait.h>
> +#include <unistd.h>
> +#include <malloc.h>
> +#include <stdlib.h>
> +
> +#include "lsm_helpers.h"
> +#include "lsm_void_hook.skel.h"
> +#include "lsm_int_hook.skel.h"
> +
> +char *LS_ARGS[] = {"true", NULL};
> +
> +int heap_mprotect(void)
> +{
> + void *buf;
> + long sz;
> +
> + sz = sysconf(_SC_PAGESIZE);
> + if (sz < 0)
> + return sz;
> +
> + buf = memalign(sz, 2 * sz);
> + if (buf == NULL)
> + return -ENOMEM;
> +
> + return mprotect(buf, sz, PROT_READ | PROT_EXEC);

"buf" is leaking memory here.

> +}
> +
> +int exec_ls(struct lsm_prog_result *result)
> +{
> + int child_pid;
> +
> + child_pid = fork();
> + if (child_pid == 0) {
> + result->monitored_pid = getpid();
> + execvp(LS_ARGS[0], LS_ARGS);
> + return -EINVAL;
> + } else if (child_pid > 0)
> + return wait(NULL);
> +
> + return -EINVAL;
> +}
> +
> +void test_lsm_void_hook(void)
> +{
> + struct lsm_prog_result *result;
> + struct lsm_void_hook *skel = NULL;
> + int err, duration = 0;
> +
> + skel = lsm_void_hook__open_and_load();
> + if (CHECK(!skel, "skel_load", "lsm_void_hook skeleton failed\n"))
> + goto close_prog;
> +
> + err = lsm_void_hook__attach(skel);
> + if (CHECK(err, "attach", "lsm_void_hook attach failed: %d\n", err))
> + goto close_prog;
> +
> + result = &skel->bss->result;
> +
> + err = exec_ls(result);
> + if (CHECK(err < 0, "exec_ls", "err %d errno %d\n", err, errno))
> + goto close_prog;
> +
> + if (CHECK(result->count != 1, "count", "count = %d", result->count))
> + goto close_prog;
> +
> + CHECK_FAIL(result->count != 1);

I think the above
if (CHECK(result->count != 1, "count", "count = %d", result->count))
goto close_prog;

CHECK_FAIL(result->count != 1);
can be replaced with
CHECK(result->count != 1, "count", "count = %d", result->count);

> +
> +close_prog:
> + lsm_void_hook__destroy(skel);
> +}
> +
> +void test_lsm_int_hook(void)
> +{
> + struct lsm_prog_result *result;
> + struct lsm_int_hook *skel = NULL;
> + int err, duration = 0;
> +
> + skel = lsm_int_hook__open_and_load();
> + if (CHECK(!skel, "skel_load", "lsm_int_hook skeleton failed\n"))
> + goto close_prog;
> +
> + err = lsm_int_hook__attach(skel);
> + if (CHECK(err, "attach", "lsm_int_hook attach failed: %d\n", err))
> + goto close_prog;
> +
> + result = &skel->bss->result;
> + result->monitored_pid = getpid();
> +
> + err = heap_mprotect();
> + if (CHECK(errno != EPERM, "heap_mprotect", "want errno=EPERM, got %d\n",
> + errno))
> + goto close_prog;
> +
> + CHECK_FAIL(result->count != 1);
> +
> +close_prog:
> + lsm_int_hook__destroy(skel);
> +}
> +
> +void test_lsm_test(void)
> +{
> + test_lsm_void_hook();
> + test_lsm_int_hook();
> +}
> diff --git a/tools/testing/selftests/bpf/progs/lsm_int_hook.c b/tools/testing/selftests/bpf/progs/lsm_int_hook.c
> new file mode 100644
> index 000000000000..1c5028ddca61
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/lsm_int_hook.c
> @@ -0,0 +1,54 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +/*
> + * Copyright 2020 Google LLC.
> + */
> +
> +#include <linux/bpf.h>
> +#include <stdbool.h>
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
> +#include <errno.h>
> +#include "lsm_helpers.h"
> +
> +char _license[] SEC("license") = "GPL";
> +
> +struct lsm_prog_result result = {
> + .monitored_pid = 0,
> + .count = 0,
> +};
> +
> +/*
> + * Define some of the structs used in the BPF program.
> + * Only the field names and their sizes need to be the
> + * same as the kernel type, the order is irrelevant.
> + */
> +struct mm_struct {
> + unsigned long start_brk, brk;
> +} __attribute__((preserve_access_index));
> +
> +struct vm_area_struct {
> + unsigned long vm_start, vm_end;
> + struct mm_struct *vm_mm;
> +} __attribute__((preserve_access_index));
> +
> +SEC("lsm/file_mprotect")
> +int BPF_PROG(test_int_hook, struct vm_area_struct *vma,
> + unsigned long reqprot, unsigned long prot, int ret)
> +{
> + if (ret != 0)
> + return ret;
> +
> + __u32 pid = bpf_get_current_pid_tgid();

In user space, we assign monitored_pid with getpid()
which is the process pid. Here
pid = bpf_get_current_pid_tgid()
actually got tid in the kernel.

Although it does not matter in this particular example,
maybe still use
bpf_get_current_pid_tgid() >> 32
to get process pid to be consistent.

The same for lsm_void_hook.c.

> + int is_heap = 0;
> +
> + is_heap = (vma->vm_start >= vma->vm_mm->start_brk &&
> + vma->vm_end <= vma->vm_mm->brk);
> +
> + if (is_heap && result.monitored_pid == pid) {
> + result.count++;
> + ret = -EPERM;
> + }
> +
> + return ret;
> +}
> diff --git a/tools/testing/selftests/bpf/progs/lsm_void_hook.c b/tools/testing/selftests/bpf/progs/lsm_void_hook.c
> new file mode 100644
> index 000000000000..4d01a8536413
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/lsm_void_hook.c
> @@ -0,0 +1,41 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +/*
> + * Copyright (C) 2020 Google LLC.
> + */
> +
> +#include <linux/bpf.h>
> +#include <stdbool.h>
> +#include <bpf/bpf_helpers.h>
> +#include <bpf/bpf_tracing.h>
> +#include <errno.h>
> +#include "lsm_helpers.h"
> +
> +char _license[] SEC("license") = "GPL";
> +
> +struct lsm_prog_result result = {
> + .monitored_pid = 0,
> + .count = 0,
> +};
> +
> +/*
> + * Define some of the structs used in the BPF program.
> + * Only the field names and their sizes need to be the
> + * same as the kernel type, the order is irrelevant.
> + */
> +struct linux_binprm {
> + const char *filename;
> +} __attribute__((preserve_access_index));
> +
> +SEC("lsm/bprm_committed_creds")
> +int BPF_PROG(test_void_hook, struct linux_binprm *bprm)
> +{
> + __u32 pid = bpf_get_current_pid_tgid();
> + char fmt[] = "lsm(bprm_committed_creds): process executed %s\n";
> +
> + bpf_trace_printk(fmt, sizeof(fmt), bprm->filename);
> + if (result.monitored_pid == pid)
> + result.count++;
> +
> + return 0;
> +}
>

Could you also upddate tools/testing/selftests/bpf/config file
so people will know what config options are needed to run the
self tests properly?