bpf: Add a selftest for bpf_ima_inode_hash

The test does the following:

- Mounts a loopback filesystem and appends the IMA policy to measure
  executions only on this file-system. Restricting the IMA policy to
  a particular filesystem prevents a system-wide IMA policy change.
- Executes an executable copied to this loopback filesystem.
- Calls the bpf_ima_inode_hash in the bprm_committed_creds hook and
  checks if the call succeeded and checks if a hash was calculated.

The test shells out to the added ima_setup.sh script as the setup is
better handled in a shell script and is more complicated to do in the
test program or even shelling out individual commands from C.

The list of required configs (i.e. IMA, SECURITYFS,
IMA_{WRITE,READ}_POLICY) for running this test are also updated.

Suggested-by: Mimi Zohar <zohar@linux.ibm.com> (limit policy rule to loopback mount)
Signed-off-by: KP Singh <kpsingh@google.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20201124151210.1081188-4-kpsingh@chromium.org

1 files changed, 28 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/progs/ima.c b/tools/testing/selftests/bpf/progs/ima.c
new file mode 100644
index 000000000000..86b21aff4bc5
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/ima.c
@@ -0,0 +1,28 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Copyright 2020 Google LLC.
+ */
+
+#include "vmlinux.h"
+#include <errno.h>
+#include <bpf/bpf_helpers.h>
+#include <bpf/bpf_tracing.h>
+
+long ima_hash_ret = -1;
+u64 ima_hash = 0;
+u32 monitored_pid = 0;
+
+char _license[] SEC("license") = "GPL";
+
+SEC("lsm.s/bprm_committed_creds")
+int BPF_PROG(ima, struct linux_binprm *bprm)
+{
+	u32 pid = bpf_get_current_pid_tgid() >> 32;
+
+	if (pid == monitored_pid)
+		ima_hash_ret = bpf_ima_inode_hash(bprm->file->f_inode,
+						  &ima_hash, sizeof(ima_hash));
+
+	return 0;
+}