[PATCH v2 3/3] selftests/bpf: Check overflow in optional buffer

[Daniel Rosenberg <drosen@google.com>]

This ensures we still reject invalid memory accesses in buffers that are
marked optional.

Signed-off-by: Daniel Rosenberg <drosen@google.com>
---
 .../testing/selftests/bpf/progs/dynptr_fail.c | 20 +++++++++++++++++++
 1 file changed, 20 insertions(+)

diff --git a/tools/testing/selftests/bpf/progs/dynptr_fail.c b/tools/testing/selftests/bpf/progs/dynptr_fail.c
index 759eb5c245cd..ee98f7ce0b0d 100644
--- a/tools/testing/selftests/bpf/progs/dynptr_fail.c
+++ b/tools/testing/selftests/bpf/progs/dynptr_fail.c
@@ -1378,3 +1378,23 @@ int invalid_slice_rdwr_rdonly(struct __sk_buff *skb)
 
 	return 0;
 }
+
+/* Buffers that are provided must be sufficiently long */
+SEC("?cgroup_skb/egress")
+__failure __msg("memory, len pair leads to invalid memory access")
+int test_dynptr_skb_small_buff(struct __sk_buff *skb)
+{
+	struct bpf_dynptr ptr;
+	char buffer[8] = {};
+	__u64 *data;
+
+	if (bpf_dynptr_from_skb(skb, 0, &ptr)) {
+		err = 1;
+		return 1;
+	}
+
+	/* This may return NULL. SKB may require a buffer */
+	data = bpf_dynptr_slice(&ptr, 0, buffer, 9);
+
+	return !!data;
+}
-- 
2.40.1.495.gc816e09b53d-goog