Re: [PATCH bpf-next v2 2/3] selftests/bpf: convert test_dev_cgroup to test_progs

[Alan Maguire <alan.maguire@oracle.com>]

On 29/07/2024 09:20, Alexis Lothoré (eBPF Foundation) wrote:
> test_dev_cgroup is defined as a standalone test program, and so is not
> executed in CI.
> 
> Convert it to test_progs framework so it is tested automatically in CI, and
> remove the old test. In order to be able to run it in test_progs, /dev/null
> must remain usable, so change the new test to test operations on devices
> 1:3 as valid, and operations on devices 1:5 (/dev/zero) as invalid.
> 
> Signed-off-by: Alexis Lothoré (eBPF Foundation) <alexis.lothore@bootlin.com>

A few small suggestions but looks great!

Reviewed-by: Alan Maguire <alan.maguire@oracle.com>

> ---
> Changes in v2:
> - pass expected return code to subtest function instead of boolean pass/not
>   pass
> - also pass buffer and buffer size for read/write subtests
> - fix faulty fd check on read/write tests expected to fail
> ---
>  tools/testing/selftests/bpf/.gitignore             |   1 -
>  tools/testing/selftests/bpf/Makefile               |   2 -
>  .../testing/selftests/bpf/prog_tests/cgroup_dev.c  | 110 +++++++++++++++++++++
>  tools/testing/selftests/bpf/test_dev_cgroup.c      |  85 ----------------
>  4 files changed, 110 insertions(+), 88 deletions(-)
> 
> diff --git a/tools/testing/selftests/bpf/.gitignore b/tools/testing/selftests/bpf/.gitignore
> index 4e4aae8aa7ec..8f14d8faeb0b 100644
> --- a/tools/testing/selftests/bpf/.gitignore
> +++ b/tools/testing/selftests/bpf/.gitignore
> @@ -9,7 +9,6 @@ test_lpm_map
>  test_tag
>  FEATURE-DUMP.libbpf
>  fixdep
> -test_dev_cgroup
>  /test_progs
>  /test_progs-no_alu32
>  /test_progs-bpf_gcc
> diff --git a/tools/testing/selftests/bpf/Makefile b/tools/testing/selftests/bpf/Makefile
> index aeada478e37a..2a9ba2246f80 100644
> --- a/tools/testing/selftests/bpf/Makefile
> +++ b/tools/testing/selftests/bpf/Makefile
> @@ -69,7 +69,6 @@ endif
>  
>  # Order correspond to 'make run_tests' order
>  TEST_GEN_PROGS = test_verifier test_tag test_maps test_lru_map test_lpm_map test_progs \
> -	test_dev_cgroup \
>  	test_sock test_sockmap get_cgroup_id_user \
>  	test_cgroup_storage \
>  	test_tcpnotify_user test_sysctl \
> @@ -295,7 +294,6 @@ JSON_WRITER		:= $(OUTPUT)/json_writer.o
>  CAP_HELPERS	:= $(OUTPUT)/cap_helpers.o
>  NETWORK_HELPERS := $(OUTPUT)/network_helpers.o
>  
> -$(OUTPUT)/test_dev_cgroup: $(CGROUP_HELPERS) $(TESTING_HELPERS)
>  $(OUTPUT)/test_skb_cgroup_id_user: $(CGROUP_HELPERS) $(TESTING_HELPERS)
>  $(OUTPUT)/test_sock: $(CGROUP_HELPERS) $(TESTING_HELPERS)
>  $(OUTPUT)/test_sockmap: $(CGROUP_HELPERS) $(TESTING_HELPERS)
> diff --git a/tools/testing/selftests/bpf/prog_tests/cgroup_dev.c b/tools/testing/selftests/bpf/prog_tests/cgroup_dev.c
> new file mode 100644
> index 000000000000..af0b70086c21
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/cgroup_dev.c
> @@ -0,0 +1,110 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <sys/stat.h>
> +#include <sys/sysmacros.h>
> +#include "test_progs.h"
> +#include "cgroup_helpers.h"
> +#include "dev_cgroup.skel.h"
> +
> +#define TEST_CGROUP "/test-bpf-based-device-cgroup/"
> +#define TEST_BUFFER_SIZE 64
> +
> +static void test_mknod(const char *path, mode_t mode, int dev_major,
> +		       int dev_minor, int expected_ret)
> +{
> +	int ret;
> +
> +	unlink(path);
> +	ret = mknod(path, mode, makedev(dev_major, dev_minor));
> +	ASSERT_EQ(ret, expected_ret, "mknod");
no need to unlink unless "if (!ret)"
> +	unlink(path);
> +}
> +
> +static void test_read(const char *path, char *buf, int buf_size, int expected_ret)
> +{
> +	int ret, fd;
> +
> +	fd = open(path, O_RDONLY);
> +
> +	/* A bare open on unauthorized device should fail */
> +	if (expected_ret < 0) {
> +		ASSERT_EQ(fd, expected_ret, "open file for read");
> +		if (fd >= 0)
> +			close(fd);
> +		return;
> +	}
> +
> +	if (!ASSERT_OK_FD(fd, "open file for read"))
> +		return;
> +
> +	ret = read(fd, buf, buf_size);
> +	ASSERT_EQ(ret, expected_ret, "read");
> +
> +	close(fd);
> +}
> +
> +static void test_write(const char *path, char *buf, int buf_size, int expected_ret)
> +{
> +	int ret, fd;
> +
> +	fd = open(path, O_WRONLY);
> +
> +	/* A bare open on unauthorized device should fail */
> +	if (expected_ret < 0) {
> +		ASSERT_EQ(fd, expected_ret, "open file for write");
> +		if (fd >= 0)
> +			close(fd);
> +		return;
> +	}
> +
> +	if (!ASSERT_OK_FD(fd, "open file for write"))
> +		return;
> +
> +	ret = write(fd, buf, buf_size);
> +	ASSERT_EQ(ret, expected_ret, "write");
> +
> +	close(fd);
> +}
> +
> +void test_cgroup_dev(void)
> +{
> +	char buf[TEST_BUFFER_SIZE] = "some random test data";
> +	struct dev_cgroup *skel;
> +	int cgroup_fd;
> +
> +	cgroup_fd = cgroup_setup_and_join(TEST_CGROUP);
> +	if (!ASSERT_OK_FD(cgroup_fd, "cgroup switch"))
> +		return;
> +
> +	skel = dev_cgroup__open_and_load();
> +	if (!ASSERT_OK_PTR(skel, "load program"))
> +		goto cleanup_cgroup;
> +
> +	if (!ASSERT_OK(bpf_prog_attach(bpf_program__fd(skel->progs.bpf_prog1),
> +				       cgroup_fd, BPF_CGROUP_DEVICE, 0),
> +		       "attach_program"))

I'd suggest using bpf_program__attach_cgroup() here as you can assign
the link in the skeleton; see prog_tests/cgroup_v1v2.c.

> +		goto cleanup_progs;
> +
> +	if (test__start_subtest("deny-mknod"))
> +		test_mknod("/dev/test_dev_cgroup_zero", S_IFCHR, 1, 5, -EPERM);
> +

nit: group with other deny subtests.

> +	if (test__start_subtest("allow-mknod"))
> +		test_mknod("/dev/test_dev_cgroup_null", S_IFCHR, 1, 3, 0);
> +
> +	if (test__start_subtest("allow-read"))
> +		test_read("/dev/urandom", buf, TEST_BUFFER_SIZE, TEST_BUFFER_SIZE);
> +

Nit: should we have a separate garbage buffer for the successful
/dev/urandom read? We're not validating buffer contents anywhere but we
will overwrite our test string I think and it'll end up non-null terminated.

Alan