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From:   Udip Pant <udippant@fb.com>
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To:     Udip Pant <udippant@fb.com>, Alexei Starovoitov <ast@kernel.org>,
        Martin KaFai Lau <kafai@fb.com>,
        Song Liu <songliubraving@fb.com>, Yonghong Song <yhs@fb.com>,
        Andrii Nakryiko <andriin@fb.com>,
        "David S . Miller" <davem@davemloft.net>
CC:     <netdev@vger.kernel.org>, <bpf@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>
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Subject: [PATCH v2 bpf 2/2] selftests/bpf: add test for freplace program with write access
Date:   Thu, 20 Aug 2020 17:28:04 -0700
Message-ID: <20200821002804.546826-2-udippant@fb.com>
In-Reply-To: <20200821002804.546826-1-udippant@fb.com>
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This adds a selftest that tests the behavior when a freplace target progr=
am
attempts to make a write access on a packet. The expectation is that the =
read or write
access is granted based on the program type of the linked program and
not itself (which is of type, for e.g., BPF_PROG_TYPE_EXT).

This test fails without the associated patch on the verifier.

Signed-off-by: Udip Pant <udippant@fb.com>
---
 .../selftests/bpf/prog_tests/fexit_bpf2bpf.c  |  1 +
 .../selftests/bpf/progs/fexit_bpf2bpf.c       | 27 +++++++++++++++++++
 .../selftests/bpf/progs/test_pkt_access.c     | 20 ++++++++++++++
 3 files changed, 48 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/fexit_bpf2bpf.c b/too=
ls/testing/selftests/bpf/prog_tests/fexit_bpf2bpf.c
index 197d0d217b56..7c7168963d52 100644
--- a/tools/testing/selftests/bpf/prog_tests/fexit_bpf2bpf.c
+++ b/tools/testing/selftests/bpf/prog_tests/fexit_bpf2bpf.c
@@ -123,6 +123,7 @@ static void test_func_replace(void)
 		"freplace/get_skb_len",
 		"freplace/get_skb_ifindex",
 		"freplace/get_constant",
+		"freplace/test_pkt_write_access_subprog",
 	};
 	test_fexit_bpf2bpf_common("./fexit_bpf2bpf.o",
 				  "./test_pkt_access.o",
diff --git a/tools/testing/selftests/bpf/progs/fexit_bpf2bpf.c b/tools/te=
sting/selftests/bpf/progs/fexit_bpf2bpf.c
index 98e1efe14549..973e8e1a6667 100644
--- a/tools/testing/selftests/bpf/progs/fexit_bpf2bpf.c
+++ b/tools/testing/selftests/bpf/progs/fexit_bpf2bpf.c
@@ -2,7 +2,9 @@
 /* Copyright (c) 2019 Facebook */
 #include <linux/stddef.h>
 #include <linux/ipv6.h>
+#include <linux/if_ether.h>
 #include <linux/bpf.h>
+#include <linux/tcp.h>
 #include <bpf/bpf_helpers.h>
 #include <bpf/bpf_endian.h>
 #include <bpf/bpf_tracing.h>
@@ -151,4 +153,29 @@ int new_get_constant(long val)
 	test_get_constant =3D 1;
 	return test_get_constant; /* original get_constant() returns val - 122 =
*/
 }
+
+__u64 test_pkt_write_access_subprog =3D 0;
+SEC("freplace/test_pkt_write_access_subprog")
+int new_test_pkt_write_access_subprog(struct __sk_buff *skb, __u32 off)
+{
+
+	void *data =3D (void *)(long)skb->data;
+	void *data_end =3D (void *)(long)skb->data_end;
+	struct tcphdr *tcp;
+
+	if (off > sizeof(struct ethhdr) + sizeof(struct ipv6hdr))
+		return -1;
+
+	tcp =3D data + off;
+	if (tcp + 1 > data_end)
+		return -1;
+
+	/* make modifications to the packet data */
+	tcp->check++;
+	tcp->syn =3D 0;
+
+	test_pkt_write_access_subprog =3D 1;
+	return 0;
+}
+
 char _license[] SEC("license") =3D "GPL";
diff --git a/tools/testing/selftests/bpf/progs/test_pkt_access.c b/tools/=
testing/selftests/bpf/progs/test_pkt_access.c
index e72eba4a93d2..c36a4731c8e0 100644
--- a/tools/testing/selftests/bpf/progs/test_pkt_access.c
+++ b/tools/testing/selftests/bpf/progs/test_pkt_access.c
@@ -79,6 +79,24 @@ int get_skb_ifindex(int val, struct __sk_buff *skb, in=
t var)
 	return skb->ifindex * val * var;
 }
=20
+__attribute__ ((noinline))
+int test_pkt_write_access_subprog(struct __sk_buff *skb, __u32 off)
+{
+	void *data =3D (void *)(long)skb->data;
+	void *data_end =3D (void *)(long)skb->data_end;
+	struct tcphdr *tcp =3D NULL;
+
+	if (off > sizeof(struct ethhdr) + sizeof(struct ipv6hdr))
+		return -1;
+
+	tcp =3D data + off;
+	if (tcp + 1 > data_end)
+		return -1;
+	/* make modification to the packet data */
+	tcp->check =3D tcp->check + 1;
+	return 0;
+}
+
 SEC("classifier/test_pkt_access")
 int test_pkt_access(struct __sk_buff *skb)
 {
@@ -117,6 +135,8 @@ int test_pkt_access(struct __sk_buff *skb)
 	if (test_pkt_access_subprog3(3, skb) !=3D skb->len * 3 * skb->ifindex)
 		return TC_ACT_SHOT;
 	if (tcp) {
+		if (test_pkt_write_access_subprog(skb, (void *)tcp - data))
+			return TC_ACT_SHOT;
 		if (((void *)(tcp) + 20) > data_end || proto !=3D 6)
 			return TC_ACT_SHOT;
 		barrier(); /* to force ordering of checks */
--=20
2.24.1