On Mon, 2023-06-05 at 18:55 +0200, Roberto Sassu wrote:
> From: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
>
> Add a simple test to ensure that the kernel and evmctl provide the same
> result for the HMAC calculation. Also add another test to evaluate the
> HMAC on a directory for which Smack added the SMACK64TRANSMUTE xattr.
>
> The second test fails without the kernel patch 'smack: Set the
> SMACK64TRANSMUTE xattr in smack_inode_init_security()', as Smack uses
> __vfs_setxattr() to set SMACK64TRANSMUTE, which does not go through EVM,
> and makes the HMAC invalid.
>
> Require (unless the UML kernel is used) that the TST_EVM_CHANGE_MODE
> environment variable is set to 1, so that users acknowledge that they are
> initializing EVM with a well-known HMAC key, which can introduce obvious
> security concerns.
>
> Signed-off-by: Roberto Sassu <roberto.sassu@xxxxxxxxxx>
Thanks, Roberto. A few suggestions inline below.
> ---
> kernel-configs/base | 4 +-
> kernel-configs/integrity | 1 +
> tests/Makefile.am | 2 +-
> tests/evm_hmac.test | 251 +++++++++++++++++++++++++++++++++++++++
> tests/functions.sh | 6 +
> 5 files changed, 262 insertions(+), 2 deletions(-)
> create mode 100755 tests/evm_hmac.test
>
> diff --git a/kernel-configs/base b/kernel-configs/base
> index 7acbd5b3b2a..6973e71f7bb 100644
> --- a/kernel-configs/base
> +++ b/kernel-configs/base
> @@ -46,11 +46,13 @@ CONFIG_TMPFS_XATTR=y
> CONFIG_CONFIGFS_FS=y
> CONFIG_KEYS=y
> CONFIG_ENCRYPTED_KEYS=y
> +CONFIG_USER_DECRYPTED_DATA=y
> CONFIG_SECURITY=y
> CONFIG_SECURITYFS=y
> CONFIG_SECURITY_NETWORK=y
> CONFIG_SECURITY_PATH=y
> -CONFIG_LSM="lockdown,yama,loadpin,safesetid,integrity,bpf"
> +CONFIG_SECURITY_SMACK=y
> +CONFIG_LSM="lockdown,yama,loadpin,safesetid,smack,bpf"
> CONFIG_CRYPTO_AEAD2=y
> CONFIG_CRYPTO_SKCIPHER=y
> CONFIG_CRYPTO_SKCIPHER2=y
> diff --git a/kernel-configs/integrity b/kernel-configs/integrity
> index a7e01e19466..2e104d205ba 100644
> --- a/kernel-configs/integrity
> +++ b/kernel-configs/integrity
> @@ -27,3 +27,4 @@ CONFIG_EVM_ATTR_FSUUID=y
> CONFIG_EVM_ADD_XATTRS=y
> CONFIG_EVM_LOAD_X509=y
> CONFIG_EVM_X509_PATH="/etc/keys/x509_evm.der"
> +CONFIG_EVM_EXTRA_SMACK_XATTRS=y
> diff --git a/tests/Makefile.am b/tests/Makefile.am
> index 03aa5b76088..a28f671398f 100644
> --- a/tests/Makefile.am
> +++ b/tests/Makefile.am
> @@ -3,7 +3,7 @@ TESTS = $(check_SCRIPTS)
>
> check_SCRIPTS += ima_hash.test sign_verify.test boot_aggregate.test \
> fsverity.test portable_signatures.test ima_policy_check.test \
> - mmap_check.test
> + mmap_check.test evm_hmac.test
>
> check_PROGRAMS := test_mmap
>
> diff --git a/tests/evm_hmac.test b/tests/evm_hmac.test
> new file mode 100755
> index 00000000000..e88ff4bf10c
> --- /dev/null
> +++ b/tests/evm_hmac.test
> @@ -0,0 +1,251 @@
> +#!/bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +#
> +# Copyright (C) 2023 Roberto Sassu <roberto.sassu@xxxxxxxxxx>
> +#
> +# Check if the kernel and evmctl provide the same result for HMAC calculation.
> +
> +trap '_report_exit_and_cleanup _cleanup_env cleanup' SIGINT SIGTERM SIGSEGV EXIT
> +
> +# Base VERBOSE on the environment variable, if set.
> +VERBOSE="${VERBOSE:-0}"
> +TST_EVM_CHANGE_MODE="${TST_EVM_CHANGE_MODE:-0}"
> +IMA_UUID="28b23254-9467-44c0-b6ba-34b12e85a26f"
> +
> +PATCHES=(
> +'KEYS: encrypted: fix key instantiation with user-provided data'
> +'KEYS: encrypted: Instantiate key with user-provided decrypted data'
> +'smack: Set the SMACK64TRANSMUTE xattr in smack_inode_init_security()'
> +)
> +
> +# From security/integrity/evm/evm.h in kernel source directory
> +(( EVM_INIT_HMAC=0x0001 ))
> +
> +cd "$(dirname "$0")" || exit 1
> +export PATH=$PWD/../src:$PATH
> +export LD_LIBRARY_PATH=$LD_LIBRARY_PATH
> +. ./functions.sh
> +_require evmctl
> +
> +cleanup() {
> + if [ "$g_loop_mounted" = "1" ]; then
> + popd > /dev/null || exit "$FAIL"
> + umount "$g_mountpoint"
> + fi
> +
> + if [ -n "$g_dev" ]; then
> + losetup -d "$g_dev"
> + fi
> +
> + if [ -n "$g_image" ]; then
> + rm -f "$g_image"
> + fi
> +
> + if [ -n "$g_mountpoint" ]; then
> + rm -Rf "$g_mountpoint"
> + fi
> +}
> +
> +get_xattr() {
> + local format="hex"
> +
> + if [ "$1" = "security.selinux" ]; then
> + format="text"
> + fi
> +
> + getfattr -n "$1" -e "$format" -d "$2" 2> /dev/null | awk -F "=" '$1 == "'"$1"'" {if ("'"$format"'" == "hex") v=substr($2, 3); else { split($2, temp, "\""); v=temp[2] }; print v}'
> +}
> +
> +# Compare HMAC calculated by the kernel with that calculated by evmctl.
> +compare_xattr() {
> + local algo=$1
> + local path=$2
> + local evm_xattr evm_xattr_evmctl true_digest
> +
> + evm_xattr="$(get_xattr security.evm "$path")"
> + true_digest=$("$algo"sum /bin/true | awk '{print $1}')
> + # evm_xattr has an extra byte at the beginning for the xattr type.
> + if [ "${#evm_xattr}" != $(( ${#true_digest} + 2 )) ]; then
> + echo "${RED}Unexpected size of security.evm for $path${NORM}"
> + return "$FAIL"
> + fi
> +
> + evm_xattr_evmctl="$(evmctl hmac --smack -v -n "$path" --uuid="$IMA_UUID" -a "$algo" --hmackey "$g_hmackey" 2>&1 | awk -F " " '$1 == "hmac:" {print $2}')"
> + if [ "$evm_xattr" != "02$evm_xattr_evmctl" ]; then
> + echo "${RED}$path security.evm mismatch between the kernel and evmctl${NORM}"
> + return "$FAIL"
> + fi
> +
> + return "$OK"
> +}
> +
> +# The purpose of this test is to verify if the kernel and evmctl produce the
> +# same HMAC.
> +check_evm_hmac() {
> + echo "Test: ${FUNCNAME[0]} (evm_hash: $1, evm_value: $g_evm_value, algo: $1, fs: $2)"
> +
> + if ! touch test-file; then
> + echo "${RED}Cannot create test-file${NORM}"
> + return "$FAIL"
> + fi
> +
> + compare_xattr "$1" test-file
> + return $?
> +}
> +
> +cleanup_evm_hmac() {
> + rm -f test-file
> +}
> +
> +# The purpose of this test is to verify that SMACK64TRANSMUTE is successfully
> +# set on a newly created directory, and that the HMAC on that directory is valid.
> +check_evm_hmac_transmute() {
> + echo "Test: ${FUNCNAME[0]} (evm_hash: $1, evm_value: $g_evm_value, algo: $1, fs: $2)"
> +
> + if ! grep -q smack < /sys/kernel/security/lsm; then
> + echo "Smack LSM not active"
> + return "${SKIP}"
> + fi
> +
> + # Add a Smack rule for transmuting of test-dir/test-dir2
> + if ! echo "_ system rwxatl" > /sys/fs/smackfs/load2; then
> + echo "${RED}Cannot set Smack policy${NORM}"
> + return "$FAIL"
> + fi
> +
> + # Smack adds security.SMACK64=_.
> + if ! mkdir test-dir; then
> + echo "${RED}Cannot create test-dir${NORM}"
> + return "$FAIL"
> + fi
> +
> + # Change the directory label so that transmuting happens.
> + if ! setfattr -n security.SMACK64 -v system test-dir; then
> + echo "${RED}Cannot set security.SMACK64 on test-dir${NORM}"
> + return "$FAIL"
> + fi
> +
> + # Add the transmute xattr so that transmuting happens.
> + if ! setfattr -n security.SMACK64TRANSMUTE -v TRUE test-dir; then
> + echo "${RED}Cannot set security.SMACK64TRANSMUTE on test-dir${NORM}"
> + return "$FAIL"
> + fi
> +
> + compare_xattr "$1" test-dir
> + result=$?
> +
> + if [ "$result" -ne "$OK" ]; then
> + return "$result"
> + fi
> +
> + # Smack adds security.SMACK64=system and security.SMACK64TRANSMUTE=TRUE.
> + if ! mkdir test-dir/test-dir2; then
> + echo "${RED}Cannot create test-dir/test-dir2${NORM}"
> + return "$FAIL"
> + fi
> +
> + compare_xattr "$1" test-dir/test-dir2
> + return $?
> +}
> +
> +cleanup_evm_hmac_transmute() {
> + rm -Rf test-dir
> +}
> +
> +_run_env "$TST_KERNEL" "$PWD/$(basename "$0")" "TST_ENV=$TST_ENV TST_KERNEL=$TST_KERNEL PATH=$PATH LD_LIBRARY_PATH=$LD_LIBRARY_PATH VERBOSE=$VERBOSE"
> +
> +# Exit from the creator of the new environment.
> +_exit_env "$TST_KERNEL"
> +
> +# Mount filesystems in the new environment.
> +_init_env
> +
> +# Assume that the EVM mode can be changed in a new environment.
> +if [ -z "$TST_ENV" ] && [ "$TST_EVM_CHANGE_MODE" -eq 0 ]; then
> + echo "${CYAN}TST_EVM_CHANGE_MODE env variable must be set to 1${NORM}"
> + exit "$SKIP"
> +fi
Perhaps also allow in a CI environment or set the TST_EVM_CHANGE_MODE
in the CI environment.
> +
> +g_lsm_init_xattr=$(awk '$1 ~ /(smack|selinux)/' < /sys/kernel/security/lsm)
> +if [ -z "$g_lsm_init_xattr" ]; then
> + echo "${CYAN}Either SMACK or SELinux must be active in the system${NORM}"
> + exit "$SKIP"
> +fi
> +
> +g_mountpoint="$(mktemp -d)"
> +g_image="$(mktemp)"
> +
> +if [ -z "$g_mountpoint" ]; then
> + echo "${RED}Mountpoint directory not created${NORM}"
> + exit "$FAIL"
> +fi
> +
> +if [ "$(whoami)" != "root" ]; then
> + echo "${CYAN}This script must be executed as root${NORM}"
> + exit "$SKIP"
> +fi
> +
> +if ! evmctl -h | grep -q hmackey; then
> + echo "${CYAN}Missing HMAC support, run: ./configure --enable-debug${NORM}"
> + exit "$SKIP"
> +fi
> +
> +if [ ! -f /sys/kernel/security/integrity/evm/evm_xattrs ] ||
> + ! grep -q SMACK64TRANSMUTE < /sys/kernel/security/integrity/evm/evm_xattrs; then
> + echo "${CYAN}Set CONFIG_EVM_ADD_XATTRS=y and CONFIG_EVM_EXTRA_SMACK_XATTRS=y in the kernel configuration${NORM}"
> + exit "$SKIP"
> +fi
Only check this when smack is enabled.
> +
> +if ! dd if=/dev/zero of="$g_image" bs=1M count=10 &> /dev/null; then
> + echo "${RED}Cannot create test image${NORM}"
> + exit "$FAIL"
> +fi
> +
> +g_dev="$(losetup -f "$g_image" --show)"
> +if [ -z "$g_dev" ]; then
> + echo "${RED}Cannot create loop device${NORM}"
> + exit "$FAIL"
> +fi
> +
> +if ! mkfs.ext4 -U $IMA_UUID -b 4096 "$g_dev" &> /dev/null; then
> + echo "${RED}Cannot format $g_dev${NORM}"
> + exit "$FAIL"
> +fi
> +
> +if ! mount "$g_dev" "$g_mountpoint"; then
> + echo "${RED}Cannot mount loop device${NORM}"
> + exit "$FAIL"
> +fi
> +
> +g_loop_mounted=1
> +chmod 777 "$g_mountpoint"
> +pushd "$g_mountpoint" > /dev/null || exit "$FAIL"
> +
> +if [ -f /sys/kernel/security/evm ]; then
> + g_evm_value=$(cat /sys/kernel/security/evm)
> +fi
> +
> +g_hmackey_data="abcdefABCDEF1234567890aaaaaaaaaaabcdefABCDEF1234567890aaaaaaaaaa"
> +
> +g_hmackey="$(mktemp)"
> +echo $g_hmackey_data | xxd -r -p > "$g_hmackey"
> +
> +if [ -n "$g_evm_value" ] && [ $((g_evm_value & EVM_INIT_HMAC)) -ne $EVM_INIT_HMAC ]; then
> + g_evm_id="$(keyctl add encrypted evm-key "new enc32 user:kmk 32 $g_hmackey_data" @u)"
> + if ! echo "$EVM_INIT_HMAC" | tee /sys/kernel/security/evm &> /dev/null; then
> + # Retry with sudo -i, to force search in the root user keyring.
> + if ! echo "$EVM_INIT_HMAC" | sudo -i tee /sys/kernel/security/evm &> /dev/null; then
> + keyctl unlink "$g_evm_id"
> + echo "${RED}Failed to initialize EVM${NORM}"
> + exit "$FAIL"
> + fi
> + fi
> +
> + g_evm_value=$(cat /sys/kernel/security/evm)
> +fi
> +
> +expect_pass_if '0 1' check_evm_hmac sha1 ext4
> +cleanup_evm_hmac
> +
> +expect_pass_if '2' check_evm_hmac_transmute sha1 ext4
> +cleanup_evm_hmac_transmute
Skip test if smack is not enabled.
--
thanks,
Mimi
