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, 80 insertions, 0 deletions

diff --git a/tools/testing/selftests/bpf/ima_setup.sh b/tools/testing/selftests/bpf/ima_setup.sh
new file mode 100755
index 000000000000..15490ccc5e55
--- /dev/null
+++ b/tools/testing/selftests/bpf/ima_setup.sh
@@ -0,0 +1,80 @@
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+set -e
+set -u
+
+IMA_POLICY_FILE="/sys/kernel/security/ima/policy"
+TEST_BINARY="/bin/true"
+
+usage()
+{
+        echo "Usage: $0 <setup|cleanup|run> <existing_tmp_dir>"
+        exit 1
+}
+
+setup()
+{
+        local tmp_dir="$1"
+        local mount_img="${tmp_dir}/test.img"
+        local mount_dir="${tmp_dir}/mnt"
+        local copied_bin_path="${mount_dir}/$(basename ${TEST_BINARY})"
+        mkdir -p ${mount_dir}
+
+        dd if=/dev/zero of="${mount_img}" bs=1M count=10
+
+        local loop_device="$(losetup --find --show ${mount_img})"
+
+        mkfs.ext4 "${loop_device}"
+        mount "${loop_device}" "${mount_dir}"
+
+        cp "${TEST_BINARY}" "${mount_dir}"
+        local mount_uuid="$(blkid -s UUID -o value ${loop_device})"
+        echo "measure func=BPRM_CHECK fsuuid=${mount_uuid}" > ${IMA_POLICY_FILE}
+}
+
+cleanup() {
+        local tmp_dir="$1"
+        local mount_img="${tmp_dir}/test.img"
+        local mount_dir="${tmp_dir}/mnt"
+
+        local loop_devices=$(losetup -j ${mount_img} -O NAME --noheadings)
+        for loop_dev in "${loop_devices}"; do
+                losetup -d $loop_dev
+        done
+
+        umount ${mount_dir}
+        rm -rf ${tmp_dir}
+}
+
+run()
+{
+        local tmp_dir="$1"
+        local mount_dir="${tmp_dir}/mnt"
+        local copied_bin_path="${mount_dir}/$(basename ${TEST_BINARY})"
+
+        exec "${copied_bin_path}"
+}
+
+main()
+{
+        [[ $# -ne 2 ]] && usage
+
+        local action="$1"
+        local tmp_dir="$2"
+
+        [[ ! -d "${tmp_dir}" ]] && echo "Directory ${tmp_dir} doesn't exist" && exit 1
+
+        if [[ "${action}" == "setup" ]]; then
+                setup "${tmp_dir}"
+        elif [[ "${action}" == "cleanup" ]]; then
+                cleanup "${tmp_dir}"
+        elif [[ "${action}" == "run" ]]; then
+                run "${tmp_dir}"
+        else
+                echo "Unknown action: ${action}"
+                exit 1
+        fi
+}
+
+main "$@"