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

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Message-ID: <20230502005218.3627530-3-drosen@google.com>
Date:   Mon,  1 May 2023 17:52:18 -0700
From:   Daniel Rosenberg <drosen@...gle.com>
To:     bpf@...r.kernel.org
Cc:     Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        John Fastabend <john.fastabend@...il.com>,
        Andrii Nakryiko <andrii@...nel.org>,
        Martin KaFai Lau <martin.lau@...ux.dev>,
        Song Liu <song@...nel.org>, Yonghong Song <yhs@...com>,
        KP Singh <kpsingh@...nel.org>,
        Stanislav Fomichev <sdf@...gle.com>,
        Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
        Shuah Khan <shuah@...nel.org>,
        Jonathan Corbet <corbet@....net>,
        Joanne Koong <joannelkoong@...il.com>,
        Mykola Lysenko <mykolal@...com>, linux-kernel@...r.kernel.org,
        linux-kselftest@...r.kernel.org, kernel-team@...roid.com,
        Daniel Rosenberg <drosen@...gle.com>
Subject: [PATCH v2 3/3] selftests/bpf: Check overflow in optional buffer

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

Signed-off-by: Daniel Rosenberg <drosen@...gle.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