linux-kernel - Re: [PATCH v2 6/6] selftests/bpf: Add test for bpf_lsm_kernel_read

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Date:   Tue, 15 Feb 2022 09:11:05 -0700
From:   Shuah Khan <skhan@...uxfoundation.org>
To:     Roberto Sassu <roberto.sassu@...wei.com>, zohar@...ux.ibm.com,
        shuah@...nel.org, ast@...nel.org, daniel@...earbox.net,
        andrii@...nel.org, kpsingh@...nel.org, revest@...omium.org
Cc:     linux-integrity@...r.kernel.org,
        linux-security-module@...r.kernel.org,
        linux-kselftest@...r.kernel.org, netdev@...r.kernel.org,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
        Shuah Khan <skhan@...uxfoundation.org>
Subject: Re: [PATCH v2 6/6] selftests/bpf: Add test for
 bpf_lsm_kernel_read_file()

On 2/15/22 5:40 AM, Roberto Sassu wrote:
> Test the ability of bpf_lsm_kernel_read_file() to call the sleepable
> functions bpf_ima_inode_hash() or bpf_ima_file_hash() to obtain a
> measurement of a loaded IMA policy.
> 
> Signed-off-by: Roberto Sassu <roberto.sassu@...wei.com>
> ---
>   tools/testing/selftests/bpf/ima_setup.sh      |  2 ++
>   .../selftests/bpf/prog_tests/test_ima.c       |  3 +-
>   tools/testing/selftests/bpf/progs/ima.c       | 28 ++++++++++++++++---
>   3 files changed, 28 insertions(+), 5 deletions(-)
> 
> diff --git a/tools/testing/selftests/bpf/ima_setup.sh b/tools/testing/selftests/bpf/ima_setup.sh
> index 8e62581113a3..82530f19f85a 100755
> --- a/tools/testing/selftests/bpf/ima_setup.sh
> +++ b/tools/testing/selftests/bpf/ima_setup.sh
> @@ -51,6 +51,7 @@ setup()
>   
>   	ensure_mount_securityfs
>   	echo "measure func=BPRM_CHECK fsuuid=${mount_uuid}" > ${IMA_POLICY_FILE}
> +	echo "measure func=BPRM_CHECK fsuuid=${mount_uuid}" > ${mount_dir}/policy_test
>   }
>   
>   cleanup() {
> @@ -74,6 +75,7 @@ run()
>   	local mount_dir="${tmp_dir}/mnt"
>   	local copied_bin_path="${mount_dir}/$(basename ${TEST_BINARY})"
>   
> +	echo ${mount_dir}/policy_test > ${IMA_POLICY_FILE}
>   	exec "${copied_bin_path}"
>   }
>   
> diff --git a/tools/testing/selftests/bpf/prog_tests/test_ima.c b/tools/testing/selftests/bpf/prog_tests/test_ima.c
> index 62bf0e830453..c4a62d7b70df 100644
> --- a/tools/testing/selftests/bpf/prog_tests/test_ima.c
> +++ b/tools/testing/selftests/bpf/prog_tests/test_ima.c
> @@ -97,8 +97,9 @@ void test_test_ima(void)
>   	/*
>   	 * 1 sample with use_ima_file_hash = false
>   	 * 2 samples with use_ima_file_hash = true (./ima_setup.sh, /bin/true)
> +	 * 1 sample with use_ima_file_hash = true (IMA policy)
>   	 */
> -	ASSERT_EQ(err, 3, "num_samples_or_err");
> +	ASSERT_EQ(err, 4, "num_samples_or_err");
>   	ASSERT_NEQ(ima_hash_from_bpf, 0, "ima_hash");
>   
>   close_clean:
> diff --git a/tools/testing/selftests/bpf/progs/ima.c b/tools/testing/selftests/bpf/progs/ima.c
> index 9bb63f96cfc0..9b4c03f30a1c 100644
> --- a/tools/testing/selftests/bpf/progs/ima.c
> +++ b/tools/testing/selftests/bpf/progs/ima.c
> @@ -20,8 +20,7 @@ char _license[] SEC("license") = "GPL";
>   
>   bool use_ima_file_hash;
>   
> -SEC("lsm.s/bprm_committed_creds")
> -void BPF_PROG(ima, struct linux_binprm *bprm)
> +static void ima_test_common(struct file *file)
>   {
>   	u64 ima_hash = 0;
>   	u64 *sample;
> @@ -31,10 +30,10 @@ void BPF_PROG(ima, struct linux_binprm *bprm)
>   	pid = bpf_get_current_pid_tgid() >> 32;
>   	if (pid == monitored_pid) {
>   		if (!use_ima_file_hash)
> -			ret = bpf_ima_inode_hash(bprm->file->f_inode, &ima_hash,
> +			ret = bpf_ima_inode_hash(file->f_inode, &ima_hash,
>   						 sizeof(ima_hash));
>   		else
> -			ret = bpf_ima_file_hash(bprm->file, &ima_hash,
> +			ret = bpf_ima_file_hash(file, &ima_hash,
>   						sizeof(ima_hash));
>   		if (ret < 0 || ima_hash == 0)

Is this considered an error? Does it make sense for this test to be
void type and not return the error to its callers? One of the callers
below seems to care for return values.

>   			return;
> @@ -49,3 +48,24 @@ void BPF_PROG(ima, struct linux_binprm *bprm)
>   
>   	return;
>   }
> +
> +SEC("lsm.s/bprm_committed_creds")
> +void BPF_PROG(ima, struct linux_binprm *bprm)
> +{
> +	ima_test_common(bprm->file);
> +}
> +
> +SEC("lsm.s/kernel_read_file")
> +int BPF_PROG(kernel_read_file, struct file *file, enum kernel_read_file_id id,
> +	     bool contents)
> +{
> +	if (!contents)
> +		return 0;
> +
> +	if (id != READING_POLICY)
> +		return 0;
> +
> +	ima_test_common(file);

This one here.

> +
> +	return 0;
> +}
> 

thanks,
-- Shuah