[PATCH bpf-next v2 2/2] selftests/hid: Cover hid_bpf_get_data() size overflow

[Yiyang Chen <chenyy23@mails.tsinghua.edu.cn>]

Add a HID-BPF regression check for hid_bpf_get_data() requests whose
size would overflow when added to the offset.

The new rdesc fixup callback asks for offset 2 and size ~0ULL, then
records whether the helper returns NULL. A vulnerable kernel returns a
non-NULL pointer because the runtime check wraps the addition. A fixed
kernel rejects the request. The test only checks the helper result and
does not dereference the returned pointer.

Also add KHDR_INCLUDES to the HID selftest build so hid_bpf.c sees the
current kernel UAPI HID definitions on systems whose installed headers do
not provide enum hid_report_type.

Signed-off-by: Yiyang Chen <chenyy23@mails.tsinghua.edu.cn>
---
 tools/testing/selftests/hid/Makefile    |  2 +-
 tools/testing/selftests/hid/hid_bpf.c   | 11 +++++++++++
 tools/testing/selftests/hid/progs/hid.c | 15 +++++++++++++++
 3 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/hid/Makefile b/tools/testing/selftests/hid/Makefile
index 50ec9e0406aba..357c6eb5ff5ee 100644
--- a/tools/testing/selftests/hid/Makefile
+++ b/tools/testing/selftests/hid/Makefile
@@ -24,7 +24,7 @@ CXX ?= $(CROSS_COMPILE)g++
 
 HOSTPKG_CONFIG := pkg-config
 
-CFLAGS += -g -O0 -rdynamic -Wall -Werror -I$(OUTPUT)
+CFLAGS += -g -O0 -rdynamic -Wall -Werror -I$(OUTPUT) $(KHDR_INCLUDES)
 CFLAGS += -I$(OUTPUT)/tools/include
 
 LDLIBS += -lelf -lz -lrt -lpthread
diff --git a/tools/testing/selftests/hid/hid_bpf.c b/tools/testing/selftests/hid/hid_bpf.c
index 1e979fb3542ba..f0a210900e63d 100644
--- a/tools/testing/selftests/hid/hid_bpf.c
+++ b/tools/testing/selftests/hid/hid_bpf.c
@@ -887,6 +887,17 @@ TEST_F(hid_bpf, test_rdesc_fixup)
 	ASSERT_EQ(rpt_desc.value[4], 0x42);
 }
 
+TEST_F(hid_bpf, test_rdesc_fixup_get_data_overflow)
+{
+	const struct test_program progs[] = {
+		{ .name = "hid_rdesc_fixup_get_data_overflow" },
+	};
+
+	LOAD_PROGRAMS(progs);
+
+	ASSERT_EQ(self->skel->bss->get_data_overflow_check, 1);
+}
+
 static int libbpf_print_fn(enum libbpf_print_level level,
 			   const char *format, va_list args)
 {
diff --git a/tools/testing/selftests/hid/progs/hid.c b/tools/testing/selftests/hid/progs/hid.c
index 5ecc845ef7921..b21fbb13c926f 100644
--- a/tools/testing/selftests/hid/progs/hid.c
+++ b/tools/testing/selftests/hid/progs/hid.c
@@ -13,6 +13,7 @@ struct attach_prog_args {
 
 __u64 callback_check = 52;
 __u64 callback2_check = 52;
+__u64 get_data_overflow_check;
 
 SEC("?struct_ops/hid_device_event")
 int BPF_PROG(hid_first_event, struct hid_bpf_ctx *hid_ctx, enum hid_report_type type)
@@ -240,6 +241,20 @@ struct hid_bpf_ops rdesc_fixup = {
 	.hid_rdesc_fixup = (void *)hid_rdesc_fixup,
 };
 
+SEC("?struct_ops.s/hid_rdesc_fixup")
+int BPF_PROG(hid_rdesc_fixup_get_data_overflow, struct hid_bpf_ctx *hid_ctx)
+{
+	if (!hid_bpf_get_data(hid_ctx, 2 /* offset */, ~0ULL /* size */))
+		get_data_overflow_check = 1;
+
+	return 0;
+}
+
+SEC(".struct_ops.link")
+struct hid_bpf_ops rdesc_fixup_get_data_overflow = {
+	.hid_rdesc_fixup = (void *)hid_rdesc_fixup_get_data_overflow,
+};
+
 SEC("?struct_ops/hid_device_event")
 int BPF_PROG(hid_test_insert1, struct hid_bpf_ctx *hid_ctx, enum hid_report_type type)
 {
-- 
2.34.1