[PATCH bpf-next 1/2] bpf: Add flag BPF_F_NO_TUNNEL_KEY to bpf_skb_set_tunnel_key()

This patch allows to remove TUNNEL_KEY from the tunnel flags bitmap
when using bpf_skb_set_tunnel_key by providing a BPF_F_NO_TUNNEL_KEY
flag. On egress, the resulting tunnel header will not contain a tunnel
key if the protocol and implementation supports it.

At the moment bpf_tunnel_key wants a user to specify a numeric tunnel
key. This will wrap the inner packet into a tunnel header with the key
bit and value set accordingly. This is problematic when using a tunnel
protocol that supports optional tunnel keys and a receiving tunnel
device that is not expecting packets with the key bit set. The receiver
won't decapsulate and drop the packet.

RFC 2890 and RFC 2784 GRE tunnels are examples where this flag is
useful. It allows for generating packets, that can be decapsulated by
a GRE tunnel device not operating in collect metadata mode or not
expecting the key bit set.

Signed-off-by: Christian Ehrig <redacted>
---
 include/uapi/linux/bpf.h       | 4 ++++
 net/core/filter.c              | 5 ++++-
 tools/include/uapi/linux/bpf.h | 4 ++++
 3 files changed, 12 insertions(+), 1 deletion(-)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 464ca3f01fe7..bc1a3d232ae4 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h

@@ -2001,6 +2001,9 @@ union bpf_attr {
  * 			sending the packet. This flag was added for GRE
  * 			encapsulation, but might be used with other protocols
  * 			as well in the future.
+ * 		**BPF_F_NO_TUNNEL_KEY**
+ * 			Add a flag to tunnel metadata indicating that no tunnel
+ * 			key should be set in the resulting tunnel header.
  *
  * 		Here is a typical usage on the transmit path:
  *

@@ -5764,6 +5767,7 @@ enum {
 	BPF_F_ZERO_CSUM_TX		= (1ULL << 1),
 	BPF_F_DONT_FRAGMENT		= (1ULL << 2),
 	BPF_F_SEQ_NUMBER		= (1ULL << 3),
+	BPF_F_NO_TUNNEL_KEY		= (1ULL << 4),
 };
 
 /* BPF_FUNC_skb_get_tunnel_key flags. */

diff --git a/net/core/filter.c b/net/core/filter.c
index 929358677183..c746e4d77214 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c

@@ -4615,7 +4615,8 @@ BPF_CALL_4(bpf_skb_set_tunnel_key, struct sk_buff *, skb,
 	struct ip_tunnel_info *info;
 
 	if (unlikely(flags & ~(BPF_F_TUNINFO_IPV6 | BPF_F_ZERO_CSUM_TX |
-			       BPF_F_DONT_FRAGMENT | BPF_F_SEQ_NUMBER)))
+			       BPF_F_DONT_FRAGMENT | BPF_F_SEQ_NUMBER |
+			       BPF_F_NO_TUNNEL_KEY)))
 		return -EINVAL;
 	if (unlikely(size != sizeof(struct bpf_tunnel_key))) {
 		switch (size) {

@@ -4653,6 +4654,8 @@ BPF_CALL_4(bpf_skb_set_tunnel_key, struct sk_buff *, skb,
 		info->key.tun_flags &= ~TUNNEL_CSUM;
 	if (flags & BPF_F_SEQ_NUMBER)
 		info->key.tun_flags |= TUNNEL_SEQ;
+	if (flags & BPF_F_NO_TUNNEL_KEY)
+		info->key.tun_flags &= ~TUNNEL_KEY;
 
 	info->key.tun_id = cpu_to_be64(from->tunnel_id);
 	info->key.tos = from->tunnel_tos;

diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 464ca3f01fe7..bc1a3d232ae4 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h

@@ -2001,6 +2001,9 @@ union bpf_attr {
  * 			sending the packet. This flag was added for GRE
  * 			encapsulation, but might be used with other protocols
  * 			as well in the future.
+ * 		**BPF_F_NO_TUNNEL_KEY**
+ * 			Add a flag to tunnel metadata indicating that no tunnel
+ * 			key should be set in the resulting tunnel header.
  *
  * 		Here is a typical usage on the transmit path:
  *

@@ -5764,6 +5767,7 @@ enum {
 	BPF_F_ZERO_CSUM_TX		= (1ULL << 1),
 	BPF_F_DONT_FRAGMENT		= (1ULL << 2),
 	BPF_F_SEQ_NUMBER		= (1ULL << 3),
+	BPF_F_NO_TUNNEL_KEY		= (1ULL << 4),
 };
 
 /* BPF_FUNC_skb_get_tunnel_key flags. */

-- 
2.37.4

This patch adds a selftest simulating a GRE sender and receiver using
tunnel headers without tunnel keys. It validates if packets encapsulated
using BPF_F_NO_TUNNEL_KEY are decapsulated by a GRE receiver not
configured with tunnel keys.

Signed-off-by: Christian Ehrig <redacted>
---
 .../selftests/bpf/progs/test_tunnel_kern.c    | 21 ++++++++++
 tools/testing/selftests/bpf/test_tunnel.sh    | 40 +++++++++++++++++--
 2 files changed, 58 insertions(+), 3 deletions(-)

diff --git a/tools/testing/selftests/bpf/progs/test_tunnel_kern.c b/tools/testing/selftests/bpf/progs/test_tunnel_kern.c
index 98af55f0bcd3..508da4a23c4f 100644
--- a/tools/testing/selftests/bpf/progs/test_tunnel_kern.c
+++ b/tools/testing/selftests/bpf/progs/test_tunnel_kern.c

@@ -81,6 +81,27 @@ int gre_set_tunnel(struct __sk_buff *skb)
 	return TC_ACT_OK;
 }
 
+SEC("tc")
+int gre_set_tunnel_no_key(struct __sk_buff *skb)
+{
+	int ret;
+	struct bpf_tunnel_key key;
+
+	__builtin_memset(&key, 0x0, sizeof(key));
+	key.remote_ipv4 = 0xac100164; /* 172.16.1.100 */
+	key.tunnel_ttl = 64;
+
+	ret = bpf_skb_set_tunnel_key(skb, &key, sizeof(key),
+				     BPF_F_ZERO_CSUM_TX | BPF_F_SEQ_NUMBER |
+				     BPF_F_NO_TUNNEL_KEY);
+	if (ret < 0) {
+		log_err(ret);
+		return TC_ACT_SHOT;
+	}
+
+	return TC_ACT_OK;
+}
+
 SEC("tc")
 int gre_get_tunnel(struct __sk_buff *skb)
 {

diff --git a/tools/testing/selftests/bpf/test_tunnel.sh b/tools/testing/selftests/bpf/test_tunnel.sh
index 2eaedc1d9ed3..06857b689c11 100755
--- a/tools/testing/selftests/bpf/test_tunnel.sh
+++ b/tools/testing/selftests/bpf/test_tunnel.sh

@@ -66,15 +66,20 @@ config_device()
 
 add_gre_tunnel()
 {
+	tun_key=
+	if [ -n "$1" ]; then
+		tun_key="key $1"
+	fi
+
 	# at_ns0 namespace
 	ip netns exec at_ns0 \
-        ip link add dev $DEV_NS type $TYPE seq key 2 \
+        ip link add dev $DEV_NS type $TYPE seq $tun_key \
 		local 172.16.1.100 remote 172.16.1.200
 	ip netns exec at_ns0 ip link set dev $DEV_NS up
 	ip netns exec at_ns0 ip addr add dev $DEV_NS 10.1.1.100/24
 
 	# root namespace
-	ip link add dev $DEV type $TYPE key 2 external
+	ip link add dev $DEV type $TYPE $tun_key external
 	ip link set dev $DEV up
 	ip addr add dev $DEV 10.1.1.200/24
 }

@@ -238,7 +243,7 @@ test_gre()
 
 	check $TYPE
 	config_device
-	add_gre_tunnel
+	add_gre_tunnel 2
 	attach_bpf $DEV gre_set_tunnel gre_get_tunnel
 	ping $PING_ARG 10.1.1.100
 	check_err $?

@@ -253,6 +258,30 @@ test_gre()
         echo -e ${GREEN}"PASS: $TYPE"${NC}
 }
 
+test_gre_no_tunnel_key()
+{
+	TYPE=gre
+	DEV_NS=gre00
+	DEV=gre11
+	ret=0
+
+	check $TYPE
+	config_device
+	add_gre_tunnel
+	attach_bpf $DEV gre_set_tunnel_no_key gre_get_tunnel
+	ping $PING_ARG 10.1.1.100
+	check_err $?
+	ip netns exec at_ns0 ping $PING_ARG 10.1.1.200
+	check_err $?
+	cleanup
+
+        if [ $ret -ne 0 ]; then
+                echo -e ${RED}"FAIL: $TYPE"${NC}
+                return 1
+        fi
+        echo -e ${GREEN}"PASS: $TYPE"${NC}
+}
+
 test_ip6gre()
 {
 	TYPE=ip6gre

@@ -589,6 +618,7 @@ cleanup()
 	ip link del ipip6tnl11 2> /dev/null
 	ip link del ip6ip6tnl11 2> /dev/null
 	ip link del gretap11 2> /dev/null
+	ip link del gre11 2> /dev/null
 	ip link del ip6gre11 2> /dev/null
 	ip link del ip6gretap11 2> /dev/null
 	ip link del geneve11 2> /dev/null

@@ -641,6 +671,10 @@ bpf_tunnel_test()
 	test_gre
 	errors=$(( $errors + $? ))
 
+	echo "Testing GRE tunnel (without tunnel keys)..."
+	test_gre_no_tunnel_key
+	errors=$(( $errors + $? ))
+
 	echo "Testing IP6GRE tunnel..."
 	test_ip6gre
 	errors=$(( $errors + $? ))

-- 
2.37.4

On 12/18, Christian Ehrig wrote:

This patch allows to remove TUNNEL_KEY from the tunnel flags bitmap
when using bpf_skb_set_tunnel_key by providing a BPF_F_NO_TUNNEL_KEY
flag. On egress, the resulting tunnel header will not contain a tunnel
key if the protocol and implementation supports it.

At the moment bpf_tunnel_key wants a user to specify a numeric tunnel
key. This will wrap the inner packet into a tunnel header with the key
bit and value set accordingly. This is problematic when using a tunnel
protocol that supports optional tunnel keys and a receiving tunnel
device that is not expecting packets with the key bit set. The receiver
won't decapsulate and drop the packet.

RFC 2890 and RFC 2784 GRE tunnels are examples where this flag is
useful. It allows for generating packets, that can be decapsulated by
a GRE tunnel device not operating in collect metadata mode or not
expecting the key bit set.

Signed-off-by: Christian Ehrig <redacted>

Acked-by: Stanislav Fomichev <redacted>

---
  include/uapi/linux/bpf.h       | 4 ++++
  net/core/filter.c              | 5 ++++-
  tools/include/uapi/linux/bpf.h | 4 ++++
  3 files changed, 12 insertions(+), 1 deletion(-)

  /* BPF_FUNC_skb_get_tunnel_key flags. */
--
2.37.4

On 12/18, Christian Ehrig wrote:

This patch adds a selftest simulating a GRE sender and receiver using
tunnel headers without tunnel keys. It validates if packets encapsulated
using BPF_F_NO_TUNNEL_KEY are decapsulated by a GRE receiver not
configured with tunnel keys.

Signed-off-by: Christian Ehrig <redacted>

Acked-by: Stanislav Fomichev <redacted>

---
  .../selftests/bpf/progs/test_tunnel_kern.c    | 21 ++++++++++
  tools/testing/selftests/bpf/test_tunnel.sh    | 40 +++++++++++++++++--
  2 files changed, 58 insertions(+), 3 deletions(-)

  add_gre_tunnel()
  {
+	tun_key=
+	if [ -n "$1" ]; then
+		tun_key="key $1"
+	fi
+
  	# at_ns0 namespace
  	ip netns exec at_ns0 \
-        ip link add dev $DEV_NS type $TYPE seq key 2 \
+        ip link add dev $DEV_NS type $TYPE seq $tun_key \
  		local 172.16.1.100 remote 172.16.1.200
  	ip netns exec at_ns0 ip link set dev $DEV_NS up
  	ip netns exec at_ns0 ip addr add dev $DEV_NS 10.1.1.100/24

+	echo "Testing GRE tunnel (without tunnel keys)..."
+	test_gre_no_tunnel_key
+	errors=$(( $errors + $? ))
+
  	echo "Testing IP6GRE tunnel..."
  	test_ip6gre
  	errors=$(( $errors + $? ))
--
2.37.4

On Sun, Dec 18, 2022 at 06:17 AM +01, Christian Ehrig wrote:

This patch allows to remove TUNNEL_KEY from the tunnel flags bitmap
when using bpf_skb_set_tunnel_key by providing a BPF_F_NO_TUNNEL_KEY
flag. On egress, the resulting tunnel header will not contain a tunnel
key if the protocol and implementation supports it.

At the moment bpf_tunnel_key wants a user to specify a numeric tunnel
key. This will wrap the inner packet into a tunnel header with the key
bit and value set accordingly. This is problematic when using a tunnel
protocol that supports optional tunnel keys and a receiving tunnel
device that is not expecting packets with the key bit set. The receiver
won't decapsulate and drop the packet.

RFC 2890 and RFC 2784 GRE tunnels are examples where this flag is
useful. It allows for generating packets, that can be decapsulated by
a GRE tunnel device not operating in collect metadata mode or not
expecting the key bit set.

Signed-off-by: Christian Ehrig <redacted>
---

Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com>

On Sun, Dec 18, 2022 at 06:17 AM +01, Christian Ehrig wrote:

This patch adds a selftest simulating a GRE sender and receiver using
tunnel headers without tunnel keys. It validates if packets encapsulated
using BPF_F_NO_TUNNEL_KEY are decapsulated by a GRE receiver not
configured with tunnel keys.

Signed-off-by: Christian Ehrig <redacted>
---

Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com>

Hello:

This series was applied to bpf/bpf-next.git (master)
by Daniel Borkmann [off-list ref]:

On Sun, 18 Dec 2022 06:17:31 +0100 you wrote:

This patch allows to remove TUNNEL_KEY from the tunnel flags bitmap
when using bpf_skb_set_tunnel_key by providing a BPF_F_NO_TUNNEL_KEY
flag. On egress, the resulting tunnel header will not contain a tunnel
key if the protocol and implementation supports it.

At the moment bpf_tunnel_key wants a user to specify a numeric tunnel
key. This will wrap the inner packet into a tunnel header with the key
bit and value set accordingly. This is problematic when using a tunnel
protocol that supports optional tunnel keys and a receiving tunnel
device that is not expecting packets with the key bit set. The receiver
won't decapsulate and drop the packet.

[...]

Here is the summary with links:
  - [bpf-next,1/2] bpf: Add flag BPF_F_NO_TUNNEL_KEY to bpf_skb_set_tunnel_key()
    https://git.kernel.org/bpf/bpf-next/c/e26aa600ba6a
  - [bpf-next,2/2] selftests/bpf: Add BPF_F_NO_TUNNEL_KEY test
    https://git.kernel.org/bpf/bpf-next/c/ac6e45e05857

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html