Re: [PATCH bpf v2 2/2] selftests/bpf: Add regression test for queue/stack map size limit

> diff --git a/tools/testing/selftests/bpf/prog_tests/queue_stack_map.c b/tools/testing/selftests/bpf/prog_tests/queue_stack_map.c
> index 41441325e179..8ab07ea77775 100644
> --- a/tools/testing/selftests/bpf/prog_tests/queue_stack_map.c
> +++ b/tools/testing/selftests/bpf/prog_tests/queue_stack_map.c
> @@ -101,8 +101,53 @@ static void test_queue_stack_map_by_type(int type)
>  	bpf_object__close(obj);
>  }
>
> +static void test_queue_stack_map_alloc_check(void)
> +{
> +	LIBBPF_OPTS(bpf_map_create_opts, opts);
> +	const __u32 big_value = 1 << 20; /* 1MB */
> +	int fd, saved_errno;
> +
> +	/*
> +	 * Regression test for the u32 index overflow in queue/stack maps:
> +	 * a map whose element storage (max_entries * value_size) exceeds
> +	 * U32_MAX bytes must be rejected at creation time, otherwise the
> +	 * u32 head/tail index multiplication wraps and push/peek/pop
> +	 * address the wrong element. 8192 * 1MB = 8GB > U32_MAX.
> +	 */
> +	fd = bpf_map_create(BPF_MAP_TYPE_QUEUE, NULL, 0, big_value, 8192, &opts);
> +	saved_errno = errno;
> +	ASSERT_LT(fd, 0, "queue_oversize_fd");
> +	ASSERT_EQ(saved_errno, E2BIG, "queue_oversize_errno");
> +
> +	/*
> +	 * max_entries == U32_MAX would make the u32 capacity counter
> +	 * qs->size (max_entries + 1) wrap to 0, permanently breaking the
> +	 * map, so it must be rejected as well.
> +	 */
> +	fd = bpf_map_create(BPF_MAP_TYPE_QUEUE, NULL, 0, 1, U32_MAX, &opts);
                                                                    ^^^^^^^

Does this build? U32_MAX is not defined in any header reachable from this
file.

U32_MAX exists only in include/linux/limits.h in the kernel tree, which is
not part of include/uapi/ and has no copy under tools/include/. The BPF
selftests include closure (test_progs.h and its dependencies) does not
provide this macro. libc provides UINT_MAX and UINT32_MAX, but not U32_MAX.

Existing selftests that need U32_MAX define it locally. In the same
directory, prog_tests/reg_bounds.c does:

  #define U32_MAX ((u32)UINT_MAX)

Since the BPF selftests Makefile builds with -Wall -Werror and every
prog_tests/*.c is linked into the single test_progs binary, this breaks the
entire selftest build rather than just this subtest.

Should this either define the macro locally (as reg_bounds.c does) or use
UINT_MAX from <limits.h>?

> +	saved_errno = errno;
> +	ASSERT_LT(fd, 0, "queue_u32max_fd");
> +	ASSERT_EQ(saved_errno, E2BIG, "queue_u32max_errno");
> +	if (fd >= 0)
> +		close(fd);
> +
> +	fd = bpf_map_create(BPF_MAP_TYPE_STACK, NULL, 0, big_value, 8192, &opts);
> +	saved_errno = errno;
> +	ASSERT_LT(fd, 0, "stack_oversize_fd");
> +	ASSERT_EQ(saved_errno, E2BIG, "stack_oversize_errno");
> +	if (fd >= 0)
> +		close(fd);
> +
> +	/* A normal-sized map must still be created successfully. */
> +	fd = bpf_map_create(BPF_MAP_TYPE_QUEUE, NULL, 0, 64, 100, &opts);
> +	ASSERT_GE(fd, 0, "queue_normal_fd");
> +	if (fd >= 0)
> +		close(fd);
> +}
> +
>  void test_queue_stack_map(void)
>  {
>  	test_queue_stack_map_by_type(QUEUE);
>  	test_queue_stack_map_by_type(STACK);
> +	test_queue_stack_map_alloc_check();
>  }


---
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/31375986836