[PATCH bpf v4 2/2] selftests/bpf: Add regression test for queue/stack map size limit

[chenyuan_fl@163.com]

From: Yuan Chen <chenyuan@kylinos.cn>

Verify that queue/stack maps whose element storage would overflow the
u32 head/tail index multiplication are rejected at creation time, and
that max_entries == U32_MAX (which would wrap the u32 capacity counter
to 0) is rejected as well.

Signed-off-by: Yuan Chen <chenyuan@kylinos.cn>
---
v4: check the bpf_map_create() return value directly instead of errno
    as suggested by Andrii Nakryiko

 .../selftests/bpf/prog_tests/queue_stack_map.c     | 37 ++++++++++++++++++++++
 1 file changed, 37 insertions(+)

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..efe808eedd9a 100644
--- a/tools/testing/selftests/bpf/prog_tests/queue_stack_map.c
+++ b/tools/testing/selftests/bpf/prog_tests/queue_stack_map.c
@@ -2,6 +2,8 @@
 #include <test_progs.h>
 #include <network_helpers.h>
 
+#define U32_MAX ((u32)UINT_MAX)
+
 enum {
 	QUEUE,
 	STACK,
@@ -101,8 +103,43 @@ 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;
+
+	/*
+	 * 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);
+	ASSERT_EQ(fd, -E2BIG, "queue_oversize");
+
+	/*
+	 * 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);
+	ASSERT_EQ(fd, -E2BIG, "queue_u32max");
+
+	fd = bpf_map_create(BPF_MAP_TYPE_STACK, NULL, 0, big_value, 8192, &opts);
+	ASSERT_EQ(fd, -E2BIG, "stack_oversize");
+
+	/* 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");
+	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();
 }
-- 
2.43.0