linux-kernel - [PATCH bpf-next 3/3] bpf: Update LSM selftests for bpf_ima_inode

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Message-Id: <20201120131708.3237864-3-kpsingh@chromium.org>
Date:   Fri, 20 Nov 2020 13:17:08 +0000
From:   KP Singh <kpsingh@...omium.org>
To:     James Morris <jmorris@...ei.org>, linux-kernel@...r.kernel.org,
        bpf@...r.kernel.org, linux-security-module@...r.kernel.org
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Florent Revest <revest@...omium.org>,
        Brendan Jackman <jackmanb@...omium.org>,
        Mimi Zohar <zohar@...ux.ibm.com>
Subject: [PATCH bpf-next 3/3] bpf: Update LSM selftests for bpf_ima_inode_hash

From: KP Singh <kpsingh@...gle.com>

- Update the IMA policy before executing the test binary (this is not an
  override of the policy, just an append that ensures that hashes are
  calculated on executions).

- Call the bpf_ima_inode_hash in the bprm_committed_creds hook and check
  if the call succeeded and a hash was calculated.

Signed-off-by: KP Singh <kpsingh@...gle.com>
---
 tools/testing/selftests/bpf/config            |  3 ++
 .../selftests/bpf/prog_tests/test_lsm.c       | 32 +++++++++++++++++++
 tools/testing/selftests/bpf/progs/lsm.c       |  7 +++-
 3 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/config b/tools/testing/selftests/bpf/config
index 2118e23ac07a..4b5764031368 100644
--- a/tools/testing/selftests/bpf/config
+++ b/tools/testing/selftests/bpf/config
@@ -39,3 +39,6 @@ CONFIG_BPF_JIT=y
 CONFIG_BPF_LSM=y
 CONFIG_SECURITY=y
 CONFIG_LIRC=y
+CONFIG_IMA=y
+CONFIG_IMA_WRITE_POLICY=y
+CONFIG_IMA_READ_POLICY=y
diff --git a/tools/testing/selftests/bpf/prog_tests/test_lsm.c b/tools/testing/selftests/bpf/prog_tests/test_lsm.c
index 6ab29226c99b..3f5d64adb233 100644
--- a/tools/testing/selftests/bpf/prog_tests/test_lsm.c
+++ b/tools/testing/selftests/bpf/prog_tests/test_lsm.c
@@ -52,6 +52,28 @@ int exec_cmd(int *monitored_pid)
 	return -EINVAL;
 }
 
+#define IMA_POLICY "measure func=BPRM_CHECK"
+
+/* This does not override the policy, IMA policy updates are
+ * append only, so this just ensures that "measure func=BPRM_CHECK"
+ * is in the policy. IMA does not allow us to remove this line once
+ * it is added.
+ */
+static int update_ima_policy(void)
+{
+	int fd, ret = 0;
+
+	fd = open("/sys/kernel/security/ima/policy", O_WRONLY);
+	if (fd < 0)
+		return -errno;
+
+	if (write(fd, IMA_POLICY, sizeof(IMA_POLICY)) == -1)
+		ret = -errno;
+
+	close(fd);
+	return ret;
+}
+
 void test_test_lsm(void)
 {
 	struct lsm *skel = NULL;
@@ -66,6 +88,10 @@ void test_test_lsm(void)
 	if (CHECK(err, "attach", "lsm attach failed: %d\n", err))
 		goto close_prog;
 
+	err = update_ima_policy();
+	if (CHECK(err != 0, "update_ima_policy", "error = %d\n", err))
+		goto close_prog;
+
 	err = exec_cmd(&skel->bss->monitored_pid);
 	if (CHECK(err < 0, "exec_cmd", "err %d errno %d\n", err, errno))
 		goto close_prog;
@@ -83,6 +109,12 @@ void test_test_lsm(void)
 	CHECK(skel->bss->mprotect_count != 1, "mprotect_count",
 	      "mprotect_count = %d\n", skel->bss->mprotect_count);
 
+	CHECK(skel->data->ima_hash_ret < 0, "ima_hash_ret",
+	      "ima_hash_ret = %d\n", skel->data->ima_hash_ret);
+
+	CHECK(skel->bss->ima_hash == 0, "ima_hash",
+	      "ima_hash = %lu\n", skel->bss->ima_hash);
+
 	syscall(__NR_setdomainname, &buf, -2L);
 	syscall(__NR_setdomainname, 0, -3L);
 	syscall(__NR_setdomainname, ~0L, -4L);
diff --git a/tools/testing/selftests/bpf/progs/lsm.c b/tools/testing/selftests/bpf/progs/lsm.c
index ff4d343b94b5..b0f9639e4b0a 100644
--- a/tools/testing/selftests/bpf/progs/lsm.c
+++ b/tools/testing/selftests/bpf/progs/lsm.c
@@ -35,6 +35,8 @@ char _license[] SEC("license") = "GPL";
 int monitored_pid = 0;
 int mprotect_count = 0;
 int bprm_count = 0;
+int ima_hash_ret = -1;
+u64 ima_hash = 0;
 
 SEC("lsm/file_mprotect")
 int BPF_PROG(test_int_hook, struct vm_area_struct *vma,
@@ -65,8 +67,11 @@ int BPF_PROG(test_void_hook, struct linux_binprm *bprm)
 	__u32 key = 0;
 	__u64 *value;
 
-	if (monitored_pid == pid)
+	if (monitored_pid == pid) {
 		bprm_count++;
+		ima_hash_ret = bpf_ima_inode_hash(bprm->file->f_inode,
+						  &ima_hash, sizeof(ima_hash));
+	}
 
 	bpf_copy_from_user(args, sizeof(args), (void *)bprm->vma->vm_mm->arg_start);
 	bpf_copy_from_user(args, sizeof(args), (void *)bprm->mm->arg_start);
-- 
2.29.2.454.gaff20da3a2-goog