Re: [PATCH bpf-next 3/3] selftests/bpf: Test linux_binprm user memory kfuncs

> diff --git a/tools/testing/selftests/bpf/prog_tests/copy_from_user_bprm.c b/tools/testing/selftests/bpf/prog_tests/copy_from_user_bprm.c
> new file mode 100644
> index 000000000000..3d5080a3975e
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/prog_tests/copy_from_user_bprm.c

[ ... ]

> +	if (!child) {
> +		char *const argv[] = { "first", "second-argument", NULL };
> +
> +		skel->bss->monitored_pid = getpid();
> +		execv("/bin/true", argv);
> +		_exit(errno);
> +	}

[ ... ]

> +	ASSERT_EQ(skel->bss->str_arg0_ret, 6, "str_arg0_ret");
> +	ASSERT_EQ(skel->bss->str_arg1_ret, 16, "str_arg1_ret");

This isn't a bug, but could these be written as sizeof("first") and
sizeof("second-argument") so the expected lengths track the argv[] strings
defined above? The literals 6 and 16 mean anyone changing an argument
string has to update three places.

> diff --git a/tools/testing/selftests/bpf/progs/copy_from_user_bprm.c b/tools/testing/selftests/bpf/progs/copy_from_user_bprm.c
> new file mode 100644
> index 000000000000..679363811edc
> --- /dev/null
> +++ b/tools/testing/selftests/bpf/progs/copy_from_user_bprm.c

[ ... ]

> +	invalid_flags_ret = bpf_copy_from_user_bprm(args, sizeof(args),
> +						    (void *)bprm->p, bprm, 1);
> +
> +	copy_ret = bpf_copy_from_user_bprm(args, sizeof(args),
> +					   (void *)bprm->p, bprm, 0);
> +	if (copy_ret)
> +		return 0;
> +
> +	args_match = !__builtin_memcmp(args, expected_args, sizeof(expected_args));
> +
> +	str_arg0_ret = bpf_copy_from_user_bprm_str(arg0, sizeof(arg0),
> +						   (void *)bprm->p, bprm,
> +						BPF_F_PAD_ZEROS);

This isn't a bug, but would an obviously out-of-range value like ~0ULL
read better than the literal 1 for the invalid-flags probe, given that
BPF_F_PAD_ZEROS is also 1? A reader has to look up the flag's value to
see the two uses are unrelated.


---
AI reviewed your patch. Please fix the bug or email reply why it's not a bug.
See: https://github.com/kernel-patches/vmtest/blob/master/ci/claude/README.md

CI run summary: https://github.com/kernel-patches/bpf/actions/runs/31592551940