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

[KP Singh]

On 23-Mär 13:04, Yonghong Song wrote:
> 
> 
> On 3/23/20 9:44 AM, KP Singh wrote:
> > From: KP Singh <kpsingh at 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 at google.com>
> > Reviewed-by: Brendan Jackman <jackmanb at google.com>
> > Reviewed-by: Florent Revest <revest at google.com>
> > Reviewed-by: Thomas Garnier <thgarnie at 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);

Thanks, and updated for test_lsm_int_hook as well.

> 
> > +
> > +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.

Done. Thanks!

> 
> > +	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?

Added CONFIG_BPF_LSM and CONFIG_SECURITY to the list.

- KP