diff mbox series

[bpf-next,6/6] selftests/bpf: add test for bpf_tcp_gen_syncookie

Message ID 20190723002042.105927-7-ppenkov.kernel@gmail.com
State Changes Requested
Delegated to: BPF Maintainers
Headers show
Series Introduce a BPF helper to generate SYN cookies | expand

Commit Message

Petar Penkov July 23, 2019, 12:20 a.m. UTC 
From: Petar Penkov <ppenkov@google.com>

Modify the existing bpf_tcp_check_syncookie test to also generate a
SYN cookie, pass the packet to the kernel, and verify that the two
cookies are the same (and both valid). Since cloned SKBs are skipped
during generic XDP, this test does not issue a SYN cookie when run in
XDP mode. We therefore only check that a valid SYN cookie was issued at
the TC hook.

Additionally, verify that the MSS for that SYN cookie is within
expected range.

Signed-off-by: Petar Penkov <ppenkov@google.com>
---
 .../bpf/progs/test_tcp_check_syncookie_kern.c | 48 +++++++++++++--
 .../selftests/bpf/test_tcp_check_syncookie.sh |  3 +
 .../bpf/test_tcp_check_syncookie_user.c       | 61 ++++++++++++++++---
 3 files changed, 99 insertions(+), 13 deletions(-)

Comments

Lorenz Bauer July 23, 2019, 9:37 a.m. UTC | #1 
On Tue, 23 Jul 2019 at 01:20, Petar Penkov <ppenkov.kernel@gmail.com> wrote:
> +static __always_inline __s64 gen_syncookie(void *data_end, struct bpf_sock *sk,
> +                                          void *iph, __u32 ip_size,
> +                                          struct tcphdr *tcph)
> +{
> +       __u32 thlen = tcph->doff * 4;
> +
> +       if (tcph->syn && !tcph->ack) {
> +               // packet should only have an MSS option
> +               if (thlen != 24)
> +                       return 0;

Just for my own understanding: without this the verifier complains since
thlen is not a known value, even though it is in bounds due to the check below?

> +
> +               if ((void *)tcph + thlen > data_end)
> +                       return 0;
> +
> +               return bpf_tcp_gen_syncookie(sk, iph, ip_size, tcph, thlen);
> +       }
> +       return 0;
> +}
> +
Alexei Starovoitov July 23, 2019, 8:46 p.m. UTC | #2 
On Tue, Jul 23, 2019 at 10:37:29AM +0100, Lorenz Bauer wrote:
> On Tue, 23 Jul 2019 at 01:20, Petar Penkov <ppenkov.kernel@gmail.com> wrote:
> > +static __always_inline __s64 gen_syncookie(void *data_end, struct bpf_sock *sk,
> > +                                          void *iph, __u32 ip_size,
> > +                                          struct tcphdr *tcph)
> > +{
> > +       __u32 thlen = tcph->doff * 4;
> > +
> > +       if (tcph->syn && !tcph->ack) {
> > +               // packet should only have an MSS option
> > +               if (thlen != 24)
> > +                       return 0;
> 
> Just for my own understanding: without this the verifier complains since
> thlen is not a known value, even though it is in bounds due to the check below?

the verifier understands only constant part of the packet pointer.
Without additional 'if' above the statement:
if ((void *)tcph + thlen > data_end)
will add variables length 'thlen' to pkt pointer which will become
another pkt pointer (with different id).
That pointer would need 'pkt + const_range > data_end' to have valid access.

We hit this issue in the past when folks wanted to use bpf_csum_diff() helper
with variable size.
It's possible to extend the verifier to support that but it's intrusive,
since variable part would need to passed around to a bunch of check* functions.
I think it's tricky, but doable. Looking forward to patches :)

> > +
> > +               if ((void *)tcph + thlen > data_end)
> > +                       return 0;
> > +
> > +               return bpf_tcp_gen_syncookie(sk, iph, ip_size, tcph, thlen);
> > +       }
> > +       return 0;
> > +}
> > +
> 
> -- 
> Lorenz Bauer  |  Systems Engineer
> 6th Floor, County Hall/The Riverside Building, SE1 7PB, UK
> 
> www.cloudflare.com
diff mbox series

Patch

diff --git a/tools/testing/selftests/bpf/progs/test_tcp_check_syncookie_kern.c b/tools/testing/selftests/bpf/progs/test_tcp_check_syncookie_kern.c
index 1ab095bcacd8..d8803dfa8d32 100644
--- a/tools/testing/selftests/bpf/progs/test_tcp_check_syncookie_kern.c
+++ b/tools/testing/selftests/bpf/progs/test_tcp_check_syncookie_kern.c
@@ -19,10 +19,29 @@ 
 struct bpf_map_def SEC("maps") results = {
 	.type = BPF_MAP_TYPE_ARRAY,
 	.key_size = sizeof(__u32),
-	.value_size = sizeof(__u64),
-	.max_entries = 1,
+	.value_size = sizeof(__u32),
+	.max_entries = 3,
 };
 
+static __always_inline __s64 gen_syncookie(void *data_end, struct bpf_sock *sk,
+					   void *iph, __u32 ip_size,
+					   struct tcphdr *tcph)
+{
+	__u32 thlen = tcph->doff * 4;
+
+	if (tcph->syn && !tcph->ack) {
+		// packet should only have an MSS option
+		if (thlen != 24)
+			return 0;
+
+		if ((void *)tcph + thlen > data_end)
+			return 0;
+
+		return bpf_tcp_gen_syncookie(sk, iph, ip_size, tcph, thlen);
+	}
+	return 0;
+}
+
 static __always_inline void check_syncookie(void *ctx, void *data,
 					    void *data_end)
 {
@@ -33,8 +52,10 @@  static __always_inline void check_syncookie(void *ctx, void *data,
 	struct ipv6hdr *ipv6h;
 	struct tcphdr *tcph;
 	int ret;
+	__u32 key_mss = 2;
+	__u32 key_gen = 1;
 	__u32 key = 0;
-	__u64 value = 1;
+	__s64 seq_mss;
 
 	ethh = data;
 	if (ethh + 1 > data_end)
@@ -66,6 +87,9 @@  static __always_inline void check_syncookie(void *ctx, void *data,
 		if (sk->state != BPF_TCP_LISTEN)
 			goto release;
 
+		seq_mss = gen_syncookie(data_end, sk, ipv4h, sizeof(*ipv4h),
+					tcph);
+
 		ret = bpf_tcp_check_syncookie(sk, ipv4h, sizeof(*ipv4h),
 					      tcph, sizeof(*tcph));
 		break;
@@ -95,6 +119,9 @@  static __always_inline void check_syncookie(void *ctx, void *data,
 		if (sk->state != BPF_TCP_LISTEN)
 			goto release;
 
+		seq_mss = gen_syncookie(data_end, sk, ipv6h, sizeof(*ipv6h),
+					tcph);
+
 		ret = bpf_tcp_check_syncookie(sk, ipv6h, sizeof(*ipv6h),
 					      tcph, sizeof(*tcph));
 		break;
@@ -103,8 +130,19 @@  static __always_inline void check_syncookie(void *ctx, void *data,
 		return;
 	}
 
-	if (ret == 0)
-		bpf_map_update_elem(&results, &key, &value, 0);
+	if (seq_mss > 0) {
+		__u32 cookie = (__u32)seq_mss;
+		__u32 mss = seq_mss >> 32;
+
+		bpf_map_update_elem(&results, &key_gen, &cookie, 0);
+		bpf_map_update_elem(&results, &key_mss, &mss, 0);
+	}
+
+	if (ret == 0) {
+		__u32 cookie = bpf_ntohl(tcph->ack_seq) - 1;
+
+		bpf_map_update_elem(&results, &key, &cookie, 0);
+	}
 
 release:
 	bpf_sk_release(sk);
diff --git a/tools/testing/selftests/bpf/test_tcp_check_syncookie.sh b/tools/testing/selftests/bpf/test_tcp_check_syncookie.sh
index d48e51716d19..9b3617d770a5 100755
--- a/tools/testing/selftests/bpf/test_tcp_check_syncookie.sh
+++ b/tools/testing/selftests/bpf/test_tcp_check_syncookie.sh
@@ -37,6 +37,9 @@  setup()
 	ns1_exec ip link set lo up
 
 	ns1_exec sysctl -w net.ipv4.tcp_syncookies=2
+	ns1_exec sysctl -w net.ipv4.tcp_window_scaling=0
+	ns1_exec sysctl -w net.ipv4.tcp_timestamps=0
+	ns1_exec sysctl -w net.ipv4.tcp_sack=0
 
 	wait_for_ip 127.0.0.1
 	wait_for_ip ::1
diff --git a/tools/testing/selftests/bpf/test_tcp_check_syncookie_user.c b/tools/testing/selftests/bpf/test_tcp_check_syncookie_user.c
index 87829c86c746..b9e991d43155 100644
--- a/tools/testing/selftests/bpf/test_tcp_check_syncookie_user.c
+++ b/tools/testing/selftests/bpf/test_tcp_check_syncookie_user.c
@@ -2,6 +2,7 @@ 
 // Copyright (c) 2018 Facebook
 // Copyright (c) 2019 Cloudflare
 
+#include <limits.h>
 #include <string.h>
 #include <stdlib.h>
 #include <unistd.h>
@@ -77,7 +78,7 @@  static int connect_to_server(int server_fd)
 	return fd;
 }
 
-static int get_map_fd_by_prog_id(int prog_id)
+static int get_map_fd_by_prog_id(int prog_id, bool *xdp)
 {
 	struct bpf_prog_info info = {};
 	__u32 info_len = sizeof(info);
@@ -104,6 +105,8 @@  static int get_map_fd_by_prog_id(int prog_id)
 		goto err;
 	}
 
+	*xdp = info.type == BPF_PROG_TYPE_XDP;
+
 	map_fd = bpf_map_get_fd_by_id(map_ids[0]);
 	if (map_fd < 0)
 		log_err("Failed to get fd by map id %d", map_ids[0]);
@@ -113,18 +116,32 @@  static int get_map_fd_by_prog_id(int prog_id)
 	return map_fd;
 }
 
-static int run_test(int server_fd, int results_fd)
+static int run_test(int server_fd, int results_fd, bool xdp)
 {
 	int client = -1, srv_client = -1;
 	int ret = 0;
 	__u32 key = 0;
-	__u64 value = 0;
+	__u32 key_gen = 1;
+	__u32 key_mss = 2;
+	__u32 value = 0;
+	__u32 value_gen = 0;
+	__u32 value_mss = 0;
 
 	if (bpf_map_update_elem(results_fd, &key, &value, 0) < 0) {
 		log_err("Can't clear results");
 		goto err;
 	}
 
+	if (bpf_map_update_elem(results_fd, &key_gen, &value_gen, 0) < 0) {
+		log_err("Can't clear results");
+		goto err;
+	}
+
+	if (bpf_map_update_elem(results_fd, &key_mss, &value_mss, 0) < 0) {
+		log_err("Can't clear results");
+		goto err;
+	}
+
 	client = connect_to_server(server_fd);
 	if (client == -1)
 		goto err;
@@ -140,8 +157,35 @@  static int run_test(int server_fd, int results_fd)
 		goto err;
 	}
 
-	if (value != 1) {
-		log_err("Didn't match syncookie: %llu", value);
+	if (value == 0) {
+		log_err("Didn't match syncookie: %u", value);
+		goto err;
+	}
+
+	if (bpf_map_lookup_elem(results_fd, &key_gen, &value_gen) < 0) {
+		log_err("Can't lookup result");
+		goto err;
+	}
+
+	if (xdp && value_gen == 0) {
+		// SYN packets do not get passed through generic XDP, skip the
+		// rest of the test.
+		printf("Skipping XDP cookie check\n");
+		goto out;
+	}
+
+	if (bpf_map_lookup_elem(results_fd, &key_mss, &value_mss) < 0) {
+		log_err("Can't lookup result");
+		goto err;
+	}
+
+	if (value != value_gen) {
+		log_err("BPF generated cookie does not match kernel one");
+		goto err;
+	}
+
+	if (value_mss < 536 || value_mss > USHRT_MAX) {
+		log_err("Unexpected MSS retrieved");
 		goto err;
 	}
 
@@ -163,13 +207,14 @@  int main(int argc, char **argv)
 	int server_v6 = -1;
 	int results = -1;
 	int err = 0;
+	bool xdp;
 
 	if (argc < 2) {
 		fprintf(stderr, "Usage: %s prog_id\n", argv[0]);
 		exit(1);
 	}
 
-	results = get_map_fd_by_prog_id(atoi(argv[1]));
+	results = get_map_fd_by_prog_id(atoi(argv[1]), &xdp);
 	if (results < 0) {
 		log_err("Can't get map");
 		goto err;
@@ -194,10 +239,10 @@  int main(int argc, char **argv)
 	if (server_v6 == -1)
 		goto err;
 
-	if (run_test(server, results))
+	if (run_test(server, results, xdp))
 		goto err;
 
-	if (run_test(server_v6, results))
+	if (run_test(server_v6, results, xdp))
 		goto err;
 
 	printf("ok\n");