[PATCH net-next v5 0/3] virtio_net: add optional flow dissection in virtio_net_hdr_to_skb

[PATCH net-next v5 0/3] virtio_net: add optional flow dissection in virtio_net_hdr_to_skb

[Tanner Love]

From: Tanner Love <tannerlove@google.com>

First patch extends the flow dissector BPF program type to accept
pointer to virtio-net header. 

Second patch uses this feature to add optional flow dissection in
virtio_net_hdr_to_skb(). This allows admins to define permitted
packets more strictly, for example dropping deprecated UDP_UFO
packets.

Third patch extends kselftest to cover this feature.

Tanner Love (3):
  net: flow_dissector: extend bpf flow dissector support with vnet hdr
  virtio_net: add optional flow dissection in virtio_net_hdr_to_skb
  selftests/net: amend bpf flow dissector prog to do vnet hdr validation

 drivers/net/bonding/bond_main.c               |   2 +-
 include/linux/skbuff.h                        |  35 ++-
 include/linux/virtio_net.h                    |  25 ++-
 include/uapi/linux/bpf.h                      |   2 +
 kernel/bpf/verifier.c                         |  50 ++++-
 net/bpf/test_run.c                            |   2 +-
 net/core/filter.c                             |  26 +++
 net/core/flow_dissector.c                     |  21 +-
 net/core/sysctl_net_core.c                    |   9 +
 tools/include/uapi/linux/bpf.h                |   2 +
 tools/testing/selftests/bpf/progs/bpf_flow.c  | 208 ++++++++++++++----
 .../selftests/bpf/test_flow_dissector.c       | 181 +++++++++++++--
 .../selftests/bpf/test_flow_dissector.sh      |  19 ++
 13 files changed, 495 insertions(+), 87 deletions(-)

-- 
2.32.0.272.g935e593368-goog

[PATCH net-next v5 1/3] net: flow_dissector: extend bpf flow dissector support with vnet hdr

[Tanner Love]

From: Tanner Love <tannerlove@google.com>

Amend the bpf flow dissector program type to be able to process
virtio-net headers. Do this to enable bpf flow dissector programs to
perform virtio-net header validation. The next patch in this series
will add a flow dissection hook in virtio_net_hdr_to_skb and make use
of this extended functionality. That commit message has more
background on the use case.

Add two new members to struct bpf_flow_keys: a pointer to struct
virtio_net_hdr, and vhdr_is_little_endian. The latter is required to
inform the BPF program of the endianness of the virtio-net header
fields, to handle the case of a version 1+ header on a big endian
machine.

Changes
v5:
  - Use PTR_TO_BTF_ID_OR_NULL instead of defining new
    PTR_TO_VNET_HDR_OR_NULL
  - Make check_flow_keys_access() disallow writes to keys->vhdr
  - Make check_flow_keys_access() check loading keys->vhdr is in
    sizeof(__u64)
  - Use BPF_REG_AX instead of BPF_REG_TMP as scratch reg
  - Describe parameter vhdr_is_little_endian in __skb_flow_dissect
    documentation
v4:
  - Add virtio_net_hdr pointer to struct bpf_flow_keys
  - Add vhdr_is_little_endian to struct bpf_flow_keys
v2:
  - Describe parameter vhdr in __skb_flow_dissect documentation

Signed-off-by: Tanner Love <tannerlove@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Petar Penkov <ppenkov@google.com>
Reviewed-by: Stanislav Fomichev <sdf@google.com>
---
 drivers/net/bonding/bond_main.c |  2 +-
 include/linux/skbuff.h          | 35 ++++++++++++++++++-----
 include/uapi/linux/bpf.h        |  2 ++
 kernel/bpf/verifier.c           | 50 ++++++++++++++++++++++++++++++---
 net/bpf/test_run.c              |  2 +-
 net/core/filter.c               | 26 +++++++++++++++++
 net/core/flow_dissector.c       | 18 +++++++++---
 tools/include/uapi/linux/bpf.h  |  2 ++
 8 files changed, 120 insertions(+), 17 deletions(-)

diff --git a/drivers/net/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index eb79a9f05914..36993636d56d 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -3554,7 +3554,7 @@ static bool bond_flow_dissect(struct bonding *bond, struct sk_buff *skb,
 	case BOND_XMIT_POLICY_ENCAP34:
 		memset(fk, 0, sizeof(*fk));
 		return __skb_flow_dissect(NULL, skb, &flow_keys_bonding,
-					  fk, NULL, 0, 0, 0, 0);
+					  fk, NULL, 0, 0, 0, 0, NULL, false);
 	default:
 		break;
 	}
diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
index b2db9cd9a73f..4e390cd8f72a 100644
--- a/include/linux/skbuff.h
+++ b/include/linux/skbuff.h
@@ -1314,21 +1314,27 @@ void skb_flow_dissector_init(struct flow_dissector *flow_dissector,
 			     unsigned int key_count);
 
 struct bpf_flow_dissector;
+struct virtio_net_hdr;
 bool bpf_flow_dissect(struct bpf_prog *prog, struct bpf_flow_dissector *ctx,
-		      __be16 proto, int nhoff, int hlen, unsigned int flags);
+		      __be16 proto, int nhoff, int hlen, unsigned int flags,
+		      const struct virtio_net_hdr *vhdr,
+		      bool vhdr_is_little_endian);
 
 bool __skb_flow_dissect(const struct net *net,
 			const struct sk_buff *skb,
 			struct flow_dissector *flow_dissector,
 			void *target_container, const void *data,
-			__be16 proto, int nhoff, int hlen, unsigned int flags);
+			__be16 proto, int nhoff, int hlen, unsigned int flags,
+			const struct virtio_net_hdr *vhdr,
+			bool vhdr_is_little_endian);
 
 static inline bool skb_flow_dissect(const struct sk_buff *skb,
 				    struct flow_dissector *flow_dissector,
 				    void *target_container, unsigned int flags)
 {
 	return __skb_flow_dissect(NULL, skb, flow_dissector,
-				  target_container, NULL, 0, 0, 0, flags);
+				  target_container, NULL, 0, 0, 0, flags, NULL,
+				  false);
 }
 
 static inline bool skb_flow_dissect_flow_keys(const struct sk_buff *skb,
@@ -1337,7 +1343,22 @@ static inline bool skb_flow_dissect_flow_keys(const struct sk_buff *skb,
 {
 	memset(flow, 0, sizeof(*flow));
 	return __skb_flow_dissect(NULL, skb, &flow_keys_dissector,
-				  flow, NULL, 0, 0, 0, flags);
+				  flow, NULL, 0, 0, 0, flags, NULL, false);
+}
+
+static inline bool
+__skb_flow_dissect_flow_keys_basic(const struct net *net,
+				   const struct sk_buff *skb,
+				   struct flow_keys_basic *flow,
+				   const void *data, __be16 proto,
+				   int nhoff, int hlen, unsigned int flags,
+				   const struct virtio_net_hdr *vhdr,
+				   bool vhdr_is_little_endian)
+{
+	memset(flow, 0, sizeof(*flow));
+	return __skb_flow_dissect(net, skb, &flow_keys_basic_dissector, flow,
+				  data, proto, nhoff, hlen, flags, vhdr,
+				  vhdr_is_little_endian);
 }
 
 static inline bool
@@ -1347,9 +1368,9 @@ skb_flow_dissect_flow_keys_basic(const struct net *net,
 				 const void *data, __be16 proto,
 				 int nhoff, int hlen, unsigned int flags)
 {
-	memset(flow, 0, sizeof(*flow));
-	return __skb_flow_dissect(net, skb, &flow_keys_basic_dissector, flow,
-				  data, proto, nhoff, hlen, flags);
+	return __skb_flow_dissect_flow_keys_basic(net, skb, flow, data, proto,
+						  nhoff, hlen, flags, NULL,
+						  false);
 }
 
 void skb_flow_dissect_meta(const struct sk_buff *skb,
diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 418b9b813d65..e1ac34548f9a 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -6017,6 +6017,8 @@ struct bpf_flow_keys {
 	};
 	__u32	flags;
 	__be32	flow_label;
+	__bpf_md_ptr(const struct virtio_net_hdr *, vhdr);
+	__u8	vhdr_is_little_endian;
 };
 
 struct bpf_func_info {
diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c
index 331b170d9fcc..989a4e3dabef 100644
--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -22,6 +22,7 @@
 #include <linux/error-injection.h>
 #include <linux/bpf_lsm.h>
 #include <linux/btf_ids.h>
+#include <linux/virtio_net.h>
 
 #include "disasm.h"
 
@@ -3373,7 +3374,7 @@ static int check_ctx_access(struct bpf_verifier_env *env, int insn_idx, int off,
 }
 
 static int check_flow_keys_access(struct bpf_verifier_env *env, int off,
-				  int size)
+				  int size, enum bpf_access_type t)
 {
 	if (size < 0 || off < 0 ||
 	    (u64)off + size > sizeof(struct bpf_flow_keys)) {
@@ -3381,6 +3382,35 @@ static int check_flow_keys_access(struct bpf_verifier_env *env, int off,
 			off, size);
 		return -EACCES;
 	}
+
+	switch (off) {
+	case offsetof(struct bpf_flow_keys, vhdr):
+		if (t == BPF_WRITE) {
+			verbose(env,
+				"invalid write to flow keys off=%d size=%d\n",
+				off, size);
+			return -EACCES;
+		}
+
+		if (size != sizeof(__u64)) {
+			verbose(env,
+				"invalid access to flow keys off=%d size=%d\n",
+				off, size);
+			return -EACCES;
+		}
+
+		break;
+	case offsetof(struct bpf_flow_keys, vhdr_is_little_endian):
+		if (t == BPF_WRITE) {
+			verbose(env,
+				"invalid write to flow keys off=%d size=%d\n",
+				off, size);
+			return -EACCES;
+		}
+
+		break;
+	}
+
 	return 0;
 }
 
@@ -4053,6 +4083,8 @@ static int check_stack_access_within_bounds(
 	return err;
 }
 
+BTF_ID_LIST_SINGLE(bpf_flow_dissector_btf_ids, struct, virtio_net_hdr);
+
 /* check whether memory at (regno + off) is accessible for t = (read | write)
  * if t==write, value_regno is a register which value is stored into memory
  * if t==read, value_regno is a register which will receive the value from memory
@@ -4217,9 +4249,19 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn
 			return -EACCES;
 		}
 
-		err = check_flow_keys_access(env, off, size);
-		if (!err && t == BPF_READ && value_regno >= 0)
-			mark_reg_unknown(env, regs, value_regno);
+		err = check_flow_keys_access(env, off, size, t);
+		if (!err && t == BPF_READ && value_regno >= 0) {
+			if (off == offsetof(struct bpf_flow_keys, vhdr)) {
+				mark_reg_known_zero(env, regs, value_regno);
+				regs[value_regno].type = PTR_TO_BTF_ID_OR_NULL;
+				regs[value_regno].btf = btf_vmlinux;
+				regs[value_regno].btf_id = bpf_flow_dissector_btf_ids[0];
+				/* required for dropping or_null */
+				regs[value_regno].id = ++env->id_gen;
+			} else {
+				mark_reg_unknown(env, regs, value_regno);
+			}
+		}
 	} else if (type_is_sk_pointer(reg->type)) {
 		if (t == BPF_WRITE) {
 			verbose(env, "R%d cannot write into %s\n",
diff --git a/net/bpf/test_run.c b/net/bpf/test_run.c
index aa47af349ba8..a11c5ce99ccb 100644
--- a/net/bpf/test_run.c
+++ b/net/bpf/test_run.c
@@ -797,7 +797,7 @@ int bpf_prog_test_run_flow_dissector(struct bpf_prog *prog,
 	bpf_test_timer_enter(&t);
 	do {
 		retval = bpf_flow_dissect(prog, &ctx, eth->h_proto, ETH_HLEN,
-					  size, flags);
+					  size, flags, NULL, false);
 	} while (bpf_test_timer_continue(&t, repeat, &ret, &duration));
 	bpf_test_timer_leave(&t);
 
diff --git a/net/core/filter.c b/net/core/filter.c
index 239de1306de9..95ff6fb31590 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -8358,6 +8358,8 @@ static bool flow_dissector_is_valid_access(int off, int size,
 			return false;
 		info->reg_type = PTR_TO_FLOW_KEYS;
 		return true;
+	case bpf_ctx_range(struct __sk_buff, len):
+		return size == size_default;
 	default:
 		return false;
 	}
@@ -8390,6 +8392,30 @@ static u32 flow_dissector_convert_ctx_access(enum bpf_access_type type,
 				      si->dst_reg, si->src_reg,
 				      offsetof(struct bpf_flow_dissector, flow_keys));
 		break;
+
+	case offsetof(struct __sk_buff, len):
+		*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(struct bpf_flow_dissector, skb),
+				      si->dst_reg, si->src_reg,
+				      offsetof(struct bpf_flow_dissector, skb));
+		*insn++ = BPF_JMP_IMM(BPF_JNE, si->dst_reg, 0, 4);
+		/* bpf_flow_dissector->skb == NULL */
+		/* dst_reg = bpf_flow_dissector->data_end */
+		*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(struct bpf_flow_dissector, data_end),
+				      si->dst_reg, si->src_reg,
+				      offsetof(struct bpf_flow_dissector, data_end));
+		/* AX = bpf_flow_dissector->data */
+		*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(struct bpf_flow_dissector, data),
+				      BPF_REG_AX, si->src_reg,
+				      offsetof(struct bpf_flow_dissector, data));
+		/* dst_reg -= bpf_flow_dissector->data */
+		*insn++ = BPF_ALU64_REG(BPF_SUB, si->dst_reg, BPF_REG_AX);
+		*insn++ = BPF_JMP_A(1);
+		/* bpf_flow_dissector->skb != NULL */
+		/* bpf_flow_dissector->skb->len */
+		*insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(struct sk_buff, len),
+				      si->dst_reg, si->dst_reg,
+				      offsetof(struct sk_buff, len));
+		break;
 	}
 
 	return insn - insn_buf;
diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
index 3ed7c98a98e1..d3df4339e0ae 100644
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -28,6 +28,7 @@
 #include <scsi/fc/fc_fcoe.h>
 #include <uapi/linux/batadv_packet.h>
 #include <linux/bpf.h>
+#include <linux/virtio_net.h>
 #if IS_ENABLED(CONFIG_NF_CONNTRACK)
 #include <net/netfilter/nf_conntrack_core.h>
 #include <net/netfilter/nf_conntrack_labels.h>
@@ -864,7 +865,9 @@ static void __skb_flow_bpf_to_target(const struct bpf_flow_keys *flow_keys,
 }
 
 bool bpf_flow_dissect(struct bpf_prog *prog, struct bpf_flow_dissector *ctx,
-		      __be16 proto, int nhoff, int hlen, unsigned int flags)
+		      __be16 proto, int nhoff, int hlen, unsigned int flags,
+		      const struct virtio_net_hdr *vhdr,
+		      bool vhdr_is_little_endian)
 {
 	struct bpf_flow_keys *flow_keys = ctx->flow_keys;
 	u32 result;
@@ -874,6 +877,8 @@ bool bpf_flow_dissect(struct bpf_prog *prog, struct bpf_flow_dissector *ctx,
 	flow_keys->n_proto = proto;
 	flow_keys->nhoff = nhoff;
 	flow_keys->thoff = flow_keys->nhoff;
+	flow_keys->vhdr = vhdr;
+	flow_keys->vhdr_is_little_endian = vhdr_is_little_endian;
 
 	BUILD_BUG_ON((int)BPF_FLOW_DISSECTOR_F_PARSE_1ST_FRAG !=
 		     (int)FLOW_DISSECTOR_F_PARSE_1ST_FRAG);
@@ -904,6 +909,8 @@ bool bpf_flow_dissect(struct bpf_prog *prog, struct bpf_flow_dissector *ctx,
  * @hlen: packet header length, if @data is NULL use skb_headlen(skb)
  * @flags: flags that control the dissection process, e.g.
  *         FLOW_DISSECTOR_F_STOP_AT_ENCAP.
+ * @vhdr: virtio_net_header to include in kernel context for BPF flow dissector
+ * @vhdr_is_little_endian: whether virtio_net_hdr fields are little endian
  *
  * The function will try to retrieve individual keys into target specified
  * by flow_dissector from either the skbuff or a raw buffer specified by the
@@ -915,7 +922,9 @@ bool __skb_flow_dissect(const struct net *net,
 			const struct sk_buff *skb,
 			struct flow_dissector *flow_dissector,
 			void *target_container, const void *data,
-			__be16 proto, int nhoff, int hlen, unsigned int flags)
+			__be16 proto, int nhoff, int hlen, unsigned int flags,
+			const struct virtio_net_hdr *vhdr,
+			bool vhdr_is_little_endian)
 {
 	struct flow_dissector_key_control *key_control;
 	struct flow_dissector_key_basic *key_basic;
@@ -1012,7 +1021,8 @@ bool __skb_flow_dissect(const struct net *net,
 
 			prog = READ_ONCE(run_array->items[0].prog);
 			ret = bpf_flow_dissect(prog, &ctx, n_proto, nhoff,
-					       hlen, flags);
+					       hlen, flags, vhdr,
+					       vhdr_is_little_endian);
 			__skb_flow_bpf_to_target(&flow_keys, flow_dissector,
 						 target_container);
 			rcu_read_unlock();
@@ -1610,7 +1620,7 @@ u32 __skb_get_hash_symmetric(const struct sk_buff *skb)
 	memset(&keys, 0, sizeof(keys));
 	__skb_flow_dissect(NULL, skb, &flow_keys_dissector_symmetric,
 			   &keys, NULL, 0, 0, 0,
-			   FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL);
+			   FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL, NULL, false);
 
 	return __flow_hash_from_keys(&keys, &hashrnd);
 }
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 418b9b813d65..e1ac34548f9a 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -6017,6 +6017,8 @@ struct bpf_flow_keys {
 	};
 	__u32	flags;
 	__be32	flow_label;
+	__bpf_md_ptr(const struct virtio_net_hdr *, vhdr);
+	__u8	vhdr_is_little_endian;
 };
 
 struct bpf_func_info {
-- 
2.32.0.272.g935e593368-goog

[PATCH net-next v5 2/3] virtio_net: add optional flow dissection in virtio_net_hdr_to_skb

[Tanner Love]

From: Tanner Love <tannerlove@google.com>

Syzkaller bugs have resulted from loose specification of
virtio_net_hdr[1]. Enable execution of a BPF flow dissector program
in virtio_net_hdr_to_skb to validate the vnet header and drop bad
input.

Introduce a new sysctl net.core.flow_dissect_vnet_hdr controlling a
static key to decide whether to perform flow dissection. When the key
is false, virtio_net_hdr_to_skb computes as before.

A permissive specification of vnet headers is part of the ABI. Some
applications now depend on it. Still, many of these packets are bogus.
Give admins the option to interpret behavior more strictly. For
instance, verifying that a VIRTIO_NET_HDR_GSO_TCPV6 header matches a
packet with unencapsulated IPv6/TCP without extension headers, with
payload length exceeding gso_size and hdr_len exactly at TCP payload
offset.

BPF flow dissection implements protocol parsing in an safe way. And is
configurable, so can be as pedantic as the workload allows (e.g.,
dropping UFO altogether).

Vnet_header flow dissection is *not* a substitute for fixing bugs when
reported. But even if not enabled continuously, offers a quick path to
mitigating vulnerabilities.

[1] https://syzkaller.appspot.com/bug?id=b419a5ca95062664fe1a60b764621eb4526e2cd0

Changes
v4:
  - Expand commit message with rationale for bpf flow dissector based
    implementation
v3:
  - Move sysctl_flow_dissect_vnet_hdr_key definition to
    flow_dissector.c to fix CONFIG_SYSCTL warning when building UML

Suggested-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Tanner Love <tannerlove@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
---
 include/linux/virtio_net.h | 25 +++++++++++++++++++++----
 net/core/flow_dissector.c  |  3 +++
 net/core/sysctl_net_core.c |  9 +++++++++
 3 files changed, 33 insertions(+), 4 deletions(-)

diff --git a/include/linux/virtio_net.h b/include/linux/virtio_net.h
index b465f8f3e554..b67b5413f2ce 100644
--- a/include/linux/virtio_net.h
+++ b/include/linux/virtio_net.h
@@ -25,10 +25,13 @@ static inline int virtio_net_hdr_set_proto(struct sk_buff *skb,
 	return 0;
 }
 
+DECLARE_STATIC_KEY_FALSE(sysctl_flow_dissect_vnet_hdr_key);
+
 static inline int virtio_net_hdr_to_skb(struct sk_buff *skb,
 					const struct virtio_net_hdr *hdr,
 					bool little_endian)
 {
+	struct flow_keys_basic keys;
 	unsigned int gso_type = 0;
 	unsigned int thlen = 0;
 	unsigned int p_off = 0;
@@ -78,13 +81,24 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *skb,
 		p_off = skb_transport_offset(skb) + thlen;
 		if (!pskb_may_pull(skb, p_off))
 			return -EINVAL;
-	} else {
+	}
+
+	/* BPF flow dissection for optional strict validation.
+	 *
+	 * Admins can define permitted packets more strictly, such as dropping
+	 * deprecated UDP_UFO packets and requiring skb->protocol to be non-zero
+	 * and matching packet headers.
+	 */
+	if (static_branch_unlikely(&sysctl_flow_dissect_vnet_hdr_key) &&
+	    !__skb_flow_dissect_flow_keys_basic(NULL, skb, &keys, NULL, 0, 0, 0,
+						0, hdr, little_endian))
+		return -EINVAL;
+
+	if (!(hdr->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM)) {
 		/* gso packets without NEEDS_CSUM do not set transport_offset.
 		 * probe and drop if does not match one of the above types.
 		 */
 		if (gso_type && skb->network_header) {
-			struct flow_keys_basic keys;
-
 			if (!skb->protocol) {
 				__be16 protocol = dev_parse_header_protocol(skb);
 
@@ -92,8 +106,11 @@ static inline int virtio_net_hdr_to_skb(struct sk_buff *skb,
 				if (protocol && protocol != skb->protocol)
 					return -EINVAL;
 			}
+
 retry:
-			if (!skb_flow_dissect_flow_keys_basic(NULL, skb, &keys,
+			/* only if flow dissection not already done */
+			if (!static_branch_unlikely(&sysctl_flow_dissect_vnet_hdr_key) &&
+			    !skb_flow_dissect_flow_keys_basic(NULL, skb, &keys,
 							      NULL, 0, 0, 0,
 							      0)) {
 				/* UFO does not specify ipv4 or 6: try both */
diff --git a/net/core/flow_dissector.c b/net/core/flow_dissector.c
index d3df4339e0ae..ce02b76d2308 100644
--- a/net/core/flow_dissector.c
+++ b/net/core/flow_dissector.c
@@ -35,6 +35,9 @@
 #endif
 #include <linux/bpf-netns.h>
 
+DEFINE_STATIC_KEY_FALSE(sysctl_flow_dissect_vnet_hdr_key);
+EXPORT_SYMBOL(sysctl_flow_dissect_vnet_hdr_key);
+
 static void dissector_set_key(struct flow_dissector *flow_dissector,
 			      enum flow_dissector_key_id key_id)
 {
diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
index c8496c1142c9..c01b9366bb75 100644
--- a/net/core/sysctl_net_core.c
+++ b/net/core/sysctl_net_core.c
@@ -36,6 +36,8 @@ static int net_msg_warn;	/* Unused, but still a sysctl */
 int sysctl_fb_tunnels_only_for_init_net __read_mostly = 0;
 EXPORT_SYMBOL(sysctl_fb_tunnels_only_for_init_net);
 
+DECLARE_STATIC_KEY_FALSE(sysctl_flow_dissect_vnet_hdr_key);
+
 /* 0 - Keep current behavior:
  *     IPv4: inherit all current settings from init_net
  *     IPv6: reset all settings to default
@@ -580,6 +582,13 @@ static struct ctl_table net_core_table[] = {
 		.extra1		= SYSCTL_ONE,
 		.extra2		= &int_3600,
 	},
+	{
+		.procname       = "flow_dissect_vnet_hdr",
+		.data           = &sysctl_flow_dissect_vnet_hdr_key.key,
+		.maxlen         = sizeof(sysctl_flow_dissect_vnet_hdr_key),
+		.mode           = 0644,
+		.proc_handler   = proc_do_static_key,
+	},
 	{ }
 };
 
-- 
2.32.0.272.g935e593368-goog

[PATCH net-next v5 3/3] selftests/net: amend bpf flow dissector prog to do vnet hdr validation

[Tanner Love]

From: Tanner Love <tannerlove@google.com>

Change the BPF flow dissector program to perform various checks on the
virtio_net_hdr fields after doing flow dissection.

Amend test_flow_dissector.(c|sh) to add test cases that inject packets
with reasonable or unreasonable virtio-net headers and assert that bad
packets are dropped and good packets are not. Do this via packet
socket; the kernel executes tpacket_snd, which enters
virtio_net_hdr_to_skb, where flow dissection / vnet header validation
occurs.

Changes
v4:
  - Read virtio_net_hdr pointer from struct bpf_flow_keys
  - Add vnet header endianness logic to BPF program

Signed-off-by: Tanner Love <tannerlove@google.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
---
 tools/testing/selftests/bpf/progs/bpf_flow.c  | 208 ++++++++++++++----
 .../selftests/bpf/test_flow_dissector.c       | 181 +++++++++++++--
 .../selftests/bpf/test_flow_dissector.sh      |  19 ++
 3 files changed, 342 insertions(+), 66 deletions(-)

diff --git a/tools/testing/selftests/bpf/progs/bpf_flow.c b/tools/testing/selftests/bpf/progs/bpf_flow.c
index 95a5a0778ed7..556e1cb1f781 100644
--- a/tools/testing/selftests/bpf/progs/bpf_flow.c
+++ b/tools/testing/selftests/bpf/progs/bpf_flow.c
@@ -13,6 +13,7 @@
 #include <linux/tcp.h>
 #include <linux/udp.h>
 #include <linux/if_packet.h>
+#include <linux/virtio_net.h>
 #include <sys/socket.h>
 #include <linux/if_tunnel.h>
 #include <linux/mpls.h>
@@ -71,15 +72,141 @@ struct {
 	__type(value, struct bpf_flow_keys);
 } last_dissection SEC(".maps");
 
-static __always_inline int export_flow_keys(struct bpf_flow_keys *keys,
+static __always_inline __u16 __virtio16_to_cpu(bool little_endian,
+					       __virtio16 val)
+{
+	if (little_endian)
+		return __le16_to_cpu((__le16)val);
+	else
+		return __be16_to_cpu((__be16)val);
+}
+
+/* Drops invalid virtio-net headers */
+static __always_inline int validate_vnet_hdr(const struct bpf_flow_keys *keys,
+					     __u32 skb_len)
+{
+	__u16 gso_type, hdr_len, gso_size, csum_start, csum_offset;
+	const struct virtio_net_hdr *vhdr = keys->vhdr;
+
+	if (!vhdr)
+		return BPF_OK;
+
+	gso_type = __virtio16_to_cpu(keys->vhdr_is_little_endian,
+				     vhdr->gso_type);
+	hdr_len = __virtio16_to_cpu(keys->vhdr_is_little_endian,
+				    vhdr->hdr_len);
+	gso_size = __virtio16_to_cpu(keys->vhdr_is_little_endian,
+				     vhdr->gso_size);
+	csum_start = __virtio16_to_cpu(keys->vhdr_is_little_endian,
+				       vhdr->csum_start);
+	csum_offset = __virtio16_to_cpu(keys->vhdr_is_little_endian,
+					vhdr->csum_offset);
+
+	/* Check gso */
+	if (gso_type != VIRTIO_NET_HDR_GSO_NONE) {
+		if (!(vhdr->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM))
+			return BPF_DROP;
+
+		if (keys->is_encap)
+			return BPF_DROP;
+
+		switch (gso_type & ~VIRTIO_NET_HDR_GSO_ECN) {
+		case VIRTIO_NET_HDR_GSO_TCPV4:
+			if (keys->addr_proto != ETH_P_IP ||
+			    keys->ip_proto != IPPROTO_TCP)
+				return BPF_DROP;
+
+			if (gso_size >= skb_len - keys->thoff -
+					sizeof(struct tcphdr))
+				return BPF_DROP;
+
+			break;
+		case VIRTIO_NET_HDR_GSO_TCPV6:
+			if (keys->addr_proto != ETH_P_IPV6 ||
+			    keys->ip_proto != IPPROTO_TCP)
+				return BPF_DROP;
+
+			if (gso_size >= skb_len - keys->thoff -
+					sizeof(struct tcphdr))
+				return BPF_DROP;
+
+			break;
+		case VIRTIO_NET_HDR_GSO_UDP:
+			if (keys->ip_proto != IPPROTO_UDP)
+				return BPF_DROP;
+
+			if (gso_size >= skb_len - keys->thoff -
+					sizeof(struct udphdr))
+				return BPF_DROP;
+
+			break;
+		default:
+			return BPF_DROP;
+		}
+	}
+
+	/* Check hdr_len */
+	if (hdr_len) {
+		switch (keys->ip_proto) {
+		case IPPROTO_TCP:
+			if (hdr_len != keys->thoff + sizeof(struct tcphdr))
+				return BPF_DROP;
+
+			break;
+		case IPPROTO_UDP:
+			if (hdr_len != keys->thoff + sizeof(struct udphdr))
+				return BPF_DROP;
+
+			break;
+		}
+	}
+
+	/* Check csum */
+	if (vhdr->flags & VIRTIO_NET_HDR_F_NEEDS_CSUM) {
+		if (keys->addr_proto != ETH_P_IP &&
+		    keys->addr_proto != ETH_P_IPV6)
+			return BPF_DROP;
+
+		if (csum_start != keys->thoff)
+			return BPF_DROP;
+
+		switch (keys->ip_proto) {
+		case IPPROTO_TCP:
+			if (csum_offset != offsetof(struct tcphdr, check))
+				return BPF_DROP;
+
+			break;
+		case IPPROTO_UDP:
+			if (csum_offset != offsetof(struct udphdr, check))
+				return BPF_DROP;
+
+			break;
+		default:
+			return BPF_DROP;
+		}
+	}
+
+	return BPF_OK;
+}
+
+/* Common steps to perform regardless of where protocol parsing finishes:
+ * 1. store flow keys in map
+ * 2. if parse result is BPF_OK, parse the vnet hdr if present
+ * 3. return the parse result
+ */
+static __always_inline int parse_epilogue(struct __sk_buff *skb,
 					    int ret)
 {
+	const struct bpf_flow_keys *keys = skb->flow_keys;
 	__u32 key = (__u32)(keys->sport) << 16 | keys->dport;
 	struct bpf_flow_keys val;
 
 	memcpy(&val, keys, sizeof(val));
 	bpf_map_update_elem(&last_dissection, &key, &val, BPF_ANY);
-	return ret;
+
+	if (ret != BPF_OK)
+		return ret;
+	return validate_vnet_hdr(keys, skb->len);
 }
 
 #define IPV6_FLOWLABEL_MASK		__bpf_constant_htonl(0x000FFFFF)
@@ -114,8 +241,6 @@ static __always_inline void *bpf_flow_dissect_get_header(struct __sk_buff *skb,
 /* Dispatches on ETHERTYPE */
 static __always_inline int parse_eth_proto(struct __sk_buff *skb, __be16 proto)
 {
-	struct bpf_flow_keys *keys = skb->flow_keys;
-
 	switch (proto) {
 	case bpf_htons(ETH_P_IP):
 		bpf_tail_call_static(skb, &jmp_table, IP);
@@ -131,12 +256,10 @@ static __always_inline int parse_eth_proto(struct __sk_buff *skb, __be16 proto)
 	case bpf_htons(ETH_P_8021AD):
 		bpf_tail_call_static(skb, &jmp_table, VLAN);
 		break;
-	default:
-		/* Protocol not supported */
-		return export_flow_keys(keys, BPF_DROP);
 	}
 
-	return export_flow_keys(keys, BPF_DROP);
+	/* Protocol not supported */
+	return parse_epilogue(skb, BPF_DROP);
 }
 
 SEC("flow_dissector")
@@ -162,28 +285,28 @@ static __always_inline int parse_ip_proto(struct __sk_buff *skb, __u8 proto)
 	case IPPROTO_ICMP:
 		icmp = bpf_flow_dissect_get_header(skb, sizeof(*icmp), &_icmp);
 		if (!icmp)
-			return export_flow_keys(keys, BPF_DROP);
-		return export_flow_keys(keys, BPF_OK);
+			return parse_epilogue(skb, BPF_DROP);
+		return parse_epilogue(skb, BPF_OK);
 	case IPPROTO_IPIP:
 		keys->is_encap = true;
 		if (keys->flags & BPF_FLOW_DISSECTOR_F_STOP_AT_ENCAP)
-			return export_flow_keys(keys, BPF_OK);
+			return parse_epilogue(skb, BPF_OK);
 
 		return parse_eth_proto(skb, bpf_htons(ETH_P_IP));
 	case IPPROTO_IPV6:
 		keys->is_encap = true;
 		if (keys->flags & BPF_FLOW_DISSECTOR_F_STOP_AT_ENCAP)
-			return export_flow_keys(keys, BPF_OK);
+			return parse_epilogue(skb, BPF_OK);
 
 		return parse_eth_proto(skb, bpf_htons(ETH_P_IPV6));
 	case IPPROTO_GRE:
 		gre = bpf_flow_dissect_get_header(skb, sizeof(*gre), &_gre);
 		if (!gre)
-			return export_flow_keys(keys, BPF_DROP);
+			return parse_epilogue(skb, BPF_DROP);
 
 		if (bpf_htons(gre->flags & GRE_VERSION))
 			/* Only inspect standard GRE packets with version 0 */
-			return export_flow_keys(keys, BPF_OK);
+			return parse_epilogue(skb, BPF_OK);
 
 		keys->thoff += sizeof(*gre); /* Step over GRE Flags and Proto */
 		if (GRE_IS_CSUM(gre->flags))
@@ -195,13 +318,13 @@ static __always_inline int parse_ip_proto(struct __sk_buff *skb, __u8 proto)
 
 		keys->is_encap = true;
 		if (keys->flags & BPF_FLOW_DISSECTOR_F_STOP_AT_ENCAP)
-			return export_flow_keys(keys, BPF_OK);
+			return parse_epilogue(skb, BPF_OK);
 
 		if (gre->proto == bpf_htons(ETH_P_TEB)) {
 			eth = bpf_flow_dissect_get_header(skb, sizeof(*eth),
 							  &_eth);
 			if (!eth)
-				return export_flow_keys(keys, BPF_DROP);
+				return parse_epilogue(skb, BPF_DROP);
 
 			keys->thoff += sizeof(*eth);
 
@@ -212,37 +335,35 @@ static __always_inline int parse_ip_proto(struct __sk_buff *skb, __u8 proto)
 	case IPPROTO_TCP:
 		tcp = bpf_flow_dissect_get_header(skb, sizeof(*tcp), &_tcp);
 		if (!tcp)
-			return export_flow_keys(keys, BPF_DROP);
+			return parse_epilogue(skb, BPF_DROP);
 
 		if (tcp->doff < 5)
-			return export_flow_keys(keys, BPF_DROP);
+			return parse_epilogue(skb, BPF_DROP);
 
 		if ((__u8 *)tcp + (tcp->doff << 2) > data_end)
-			return export_flow_keys(keys, BPF_DROP);
+			return parse_epilogue(skb, BPF_DROP);
 
 		keys->sport = tcp->source;
 		keys->dport = tcp->dest;
-		return export_flow_keys(keys, BPF_OK);
+		return parse_epilogue(skb, BPF_OK);
 	case IPPROTO_UDP:
 	case IPPROTO_UDPLITE:
 		udp = bpf_flow_dissect_get_header(skb, sizeof(*udp), &_udp);
 		if (!udp)
-			return export_flow_keys(keys, BPF_DROP);
+			return parse_epilogue(skb, BPF_DROP);
 
 		keys->sport = udp->source;
 		keys->dport = udp->dest;
-		return export_flow_keys(keys, BPF_OK);
+		return parse_epilogue(skb, BPF_OK);
 	default:
-		return export_flow_keys(keys, BPF_DROP);
+		return parse_epilogue(skb, BPF_DROP);
 	}
 
-	return export_flow_keys(keys, BPF_DROP);
+	return parse_epilogue(skb, BPF_DROP);
 }
 
 static __always_inline int parse_ipv6_proto(struct __sk_buff *skb, __u8 nexthdr)
 {
-	struct bpf_flow_keys *keys = skb->flow_keys;
-
 	switch (nexthdr) {
 	case IPPROTO_HOPOPTS:
 	case IPPROTO_DSTOPTS:
@@ -255,7 +376,7 @@ static __always_inline int parse_ipv6_proto(struct __sk_buff *skb, __u8 nexthdr)
 		return parse_ip_proto(skb, nexthdr);
 	}
 
-	return export_flow_keys(keys, BPF_DROP);
+	return parse_epilogue(skb, BPF_DROP);
 }
 
 PROG(IP)(struct __sk_buff *skb)
@@ -268,11 +389,11 @@ PROG(IP)(struct __sk_buff *skb)
 
 	iph = bpf_flow_dissect_get_header(skb, sizeof(*iph), &_iph);
 	if (!iph)
-		return export_flow_keys(keys, BPF_DROP);
+		return parse_epilogue(skb, BPF_DROP);
 
 	/* IP header cannot be smaller than 20 bytes */
 	if (iph->ihl < 5)
-		return export_flow_keys(keys, BPF_DROP);
+		return parse_epilogue(skb, BPF_DROP);
 
 	keys->addr_proto = ETH_P_IP;
 	keys->ipv4_src = iph->saddr;
@@ -281,7 +402,7 @@ PROG(IP)(struct __sk_buff *skb)
 
 	keys->thoff += iph->ihl << 2;
 	if (data + keys->thoff > data_end)
-		return export_flow_keys(keys, BPF_DROP);
+		return parse_epilogue(skb, BPF_DROP);
 
 	if (iph->frag_off & bpf_htons(IP_MF | IP_OFFSET)) {
 		keys->is_frag = true;
@@ -302,7 +423,7 @@ PROG(IP)(struct __sk_buff *skb)
 	}
 
 	if (done)
-		return export_flow_keys(keys, BPF_OK);
+		return parse_epilogue(skb, BPF_OK);
 
 	return parse_ip_proto(skb, iph->protocol);
 }
@@ -314,7 +435,7 @@ PROG(IPV6)(struct __sk_buff *skb)
 
 	ip6h = bpf_flow_dissect_get_header(skb, sizeof(*ip6h), &_ip6h);
 	if (!ip6h)
-		return export_flow_keys(keys, BPF_DROP);
+		return parse_epilogue(skb, BPF_DROP);
 
 	keys->addr_proto = ETH_P_IPV6;
 	memcpy(&keys->ipv6_src, &ip6h->saddr, 2*sizeof(ip6h->saddr));
@@ -324,7 +445,7 @@ PROG(IPV6)(struct __sk_buff *skb)
 	keys->flow_label = ip6_flowlabel(ip6h);
 
 	if (keys->flags & BPF_FLOW_DISSECTOR_F_STOP_AT_FLOW_LABEL)
-		return export_flow_keys(keys, BPF_OK);
+		return parse_epilogue(skb, BPF_OK);
 
 	return parse_ipv6_proto(skb, ip6h->nexthdr);
 }
@@ -336,7 +457,7 @@ PROG(IPV6OP)(struct __sk_buff *skb)
 
 	ip6h = bpf_flow_dissect_get_header(skb, sizeof(*ip6h), &_ip6h);
 	if (!ip6h)
-		return export_flow_keys(keys, BPF_DROP);
+		return parse_epilogue(skb, BPF_DROP);
 
 	/* hlen is in 8-octets and does not include the first 8 bytes
 	 * of the header
@@ -354,7 +475,7 @@ PROG(IPV6FR)(struct __sk_buff *skb)
 
 	fragh = bpf_flow_dissect_get_header(skb, sizeof(*fragh), &_fragh);
 	if (!fragh)
-		return export_flow_keys(keys, BPF_DROP);
+		return parse_epilogue(skb, BPF_DROP);
 
 	keys->thoff += sizeof(*fragh);
 	keys->is_frag = true;
@@ -367,9 +488,9 @@ PROG(IPV6FR)(struct __sk_buff *skb)
 		 * explicitly asked for.
 		 */
 		if (!(keys->flags & BPF_FLOW_DISSECTOR_F_PARSE_1ST_FRAG))
-			return export_flow_keys(keys, BPF_OK);
+			return parse_epilogue(skb, BPF_OK);
 	} else {
-		return export_flow_keys(keys, BPF_OK);
+		return parse_epilogue(skb, BPF_OK);
 	}
 
 	return parse_ipv6_proto(skb, fragh->nexthdr);
@@ -377,14 +498,13 @@ PROG(IPV6FR)(struct __sk_buff *skb)
 
 PROG(MPLS)(struct __sk_buff *skb)
 {
-	struct bpf_flow_keys *keys = skb->flow_keys;
 	struct mpls_label *mpls, _mpls;
 
 	mpls = bpf_flow_dissect_get_header(skb, sizeof(*mpls), &_mpls);
 	if (!mpls)
-		return export_flow_keys(keys, BPF_DROP);
+		return parse_epilogue(skb, BPF_DROP);
 
-	return export_flow_keys(keys, BPF_OK);
+	return parse_epilogue(skb, BPF_OK);
 }
 
 PROG(VLAN)(struct __sk_buff *skb)
@@ -396,10 +516,10 @@ PROG(VLAN)(struct __sk_buff *skb)
 	if (keys->n_proto == bpf_htons(ETH_P_8021AD)) {
 		vlan = bpf_flow_dissect_get_header(skb, sizeof(*vlan), &_vlan);
 		if (!vlan)
-			return export_flow_keys(keys, BPF_DROP);
+			return parse_epilogue(skb, BPF_DROP);
 
 		if (vlan->h_vlan_encapsulated_proto != bpf_htons(ETH_P_8021Q))
-			return export_flow_keys(keys, BPF_DROP);
+			return parse_epilogue(skb, BPF_DROP);
 
 		keys->nhoff += sizeof(*vlan);
 		keys->thoff += sizeof(*vlan);
@@ -407,14 +527,14 @@ PROG(VLAN)(struct __sk_buff *skb)
 
 	vlan = bpf_flow_dissect_get_header(skb, sizeof(*vlan), &_vlan);
 	if (!vlan)
-		return export_flow_keys(keys, BPF_DROP);
+		return parse_epilogue(skb, BPF_DROP);
 
 	keys->nhoff += sizeof(*vlan);
 	keys->thoff += sizeof(*vlan);
 	/* Only allow 8021AD + 8021Q double tagging and no triple tagging.*/
 	if (vlan->h_vlan_encapsulated_proto == bpf_htons(ETH_P_8021AD) ||
 	    vlan->h_vlan_encapsulated_proto == bpf_htons(ETH_P_8021Q))
-		return export_flow_keys(keys, BPF_DROP);
+		return parse_epilogue(skb, BPF_DROP);
 
 	keys->n_proto = vlan->h_vlan_encapsulated_proto;
 	return parse_eth_proto(skb, vlan->h_vlan_encapsulated_proto);
diff --git a/tools/testing/selftests/bpf/test_flow_dissector.c b/tools/testing/selftests/bpf/test_flow_dissector.c
index 571cc076dd7d..aa80055a5518 100644
--- a/tools/testing/selftests/bpf/test_flow_dissector.c
+++ b/tools/testing/selftests/bpf/test_flow_dissector.c
@@ -17,6 +17,8 @@
 #include <linux/if_packet.h>
 #include <linux/if_ether.h>
 #include <linux/ipv6.h>
+#include <linux/virtio_net.h>
+#include <net/if.h>
 #include <netinet/ip.h>
 #include <netinet/in.h>
 #include <netinet/udp.h>
@@ -65,7 +67,8 @@ struct guehdr {
 static uint8_t	cfg_dsfield_inner;
 static uint8_t	cfg_dsfield_outer;
 static uint8_t	cfg_encap_proto;
-static bool	cfg_expect_failure = false;
+static bool	cfg_expect_norx;
+static bool	cfg_expect_snd_failure;
 static int	cfg_l3_extra = AF_UNSPEC;	/* optional SIT prefix */
 static int	cfg_l3_inner = AF_UNSPEC;
 static int	cfg_l3_outer = AF_UNSPEC;
@@ -77,8 +80,14 @@ static int	cfg_port_gue = 6080;
 static bool	cfg_only_rx;
 static bool	cfg_only_tx;
 static int	cfg_src_port = 9;
+static bool	cfg_tx_pf_packet;
+static bool	cfg_use_vnet;
+static bool	cfg_vnet_use_hdr_len_bad;
+static bool	cfg_vnet_use_gso;
+static bool	cfg_vnet_use_csum_off;
+static bool	cfg_partial_udp_hdr;
 
-static char	buf[ETH_DATA_LEN];
+static char	buf[ETH_MAX_MTU];
 
 #define INIT_ADDR4(name, addr4, port)				\
 	static struct sockaddr_in name = {			\
@@ -273,8 +282,48 @@ static int l3_length(int family)
 		return sizeof(struct ipv6hdr);
 }
 
+static int build_vnet_header(void *header, int il3_len)
+{
+	struct virtio_net_hdr *vh = header;
+
+	vh->hdr_len = ETH_HLEN + il3_len + sizeof(struct udphdr);
+
+	if (cfg_partial_udp_hdr) {
+		vh->hdr_len -= (sizeof(struct udphdr) >> 1);
+		return sizeof(*vh);
+	}
+
+	/* Alteration must increase hdr_len; if not, kernel overwrites it */
+	if (cfg_vnet_use_hdr_len_bad)
+		vh->hdr_len++;
+
+	if (cfg_vnet_use_csum_off) {
+		vh->flags |= VIRTIO_NET_HDR_F_NEEDS_CSUM;
+		vh->csum_start = ETH_HLEN + il3_len;
+		vh->csum_offset = __builtin_offsetof(struct udphdr, check);
+	}
+
+	if (cfg_vnet_use_gso) {
+		vh->gso_type = VIRTIO_NET_HDR_GSO_UDP;
+		vh->gso_size = ETH_DATA_LEN - il3_len;
+	}
+
+	return sizeof(*vh);
+}
+
+static int build_eth_header(void *header)
+{
+	struct ethhdr *eth = header;
+	uint16_t proto = cfg_l3_inner == PF_INET ? ETH_P_IP : ETH_P_IPV6;
+
+	eth->h_proto = htons(proto);
+
+	return ETH_HLEN;
+}
+
 static int build_packet(void)
 {
+	int l2_len = 0;
 	int ol3_len = 0, ol4_len = 0, il3_len = 0, il4_len = 0;
 	int el3_len = 0;
 
@@ -294,23 +343,29 @@ static int build_packet(void)
 	il3_len = l3_length(cfg_l3_inner);
 	il4_len = sizeof(struct udphdr);
 
-	if (el3_len + ol3_len + ol4_len + il3_len + il4_len + cfg_payload_len >=
-	    sizeof(buf))
+	if (cfg_use_vnet)
+		l2_len += build_vnet_header(buf, il3_len);
+	if (cfg_tx_pf_packet)
+		l2_len += build_eth_header(buf + l2_len);
+
+	if (l2_len + el3_len + ol3_len + ol4_len + il3_len + il4_len +
+	    cfg_payload_len >= sizeof(buf))
 		error(1, 0, "packet too large\n");
 
 	/*
 	 * Fill packet from inside out, to calculate correct checksums.
 	 * But create ip before udp headers, as udp uses ip for pseudo-sum.
 	 */
-	memset(buf + el3_len + ol3_len + ol4_len + il3_len + il4_len,
+	memset(buf + l2_len + el3_len + ol3_len + ol4_len + il3_len + il4_len,
 	       cfg_payload_char, cfg_payload_len);
 
 	/* add zero byte for udp csum padding */
-	buf[el3_len + ol3_len + ol4_len + il3_len + il4_len + cfg_payload_len] = 0;
+	buf[l2_len + el3_len + ol3_len + ol4_len + il3_len + il4_len +
+	    cfg_payload_len] = 0;
 
 	switch (cfg_l3_inner) {
 	case PF_INET:
-		build_ipv4_header(buf + el3_len + ol3_len + ol4_len,
+		build_ipv4_header(buf + l2_len + el3_len + ol3_len + ol4_len,
 				  IPPROTO_UDP,
 				  in_saddr4.sin_addr.s_addr,
 				  in_daddr4.sin_addr.s_addr,
@@ -318,7 +373,7 @@ static int build_packet(void)
 				  cfg_dsfield_inner);
 		break;
 	case PF_INET6:
-		build_ipv6_header(buf + el3_len + ol3_len + ol4_len,
+		build_ipv6_header(buf + l2_len + el3_len + ol3_len + ol4_len,
 				  IPPROTO_UDP,
 				  &in_saddr6, &in_daddr6,
 				  il4_len + cfg_payload_len,
@@ -326,22 +381,25 @@ static int build_packet(void)
 		break;
 	}
 
-	build_udp_header(buf + el3_len + ol3_len + ol4_len + il3_len,
+	build_udp_header(buf + l2_len + el3_len + ol3_len + ol4_len + il3_len,
 			 cfg_payload_len, CFG_PORT_INNER, cfg_l3_inner);
 
+	if (cfg_partial_udp_hdr)
+		return l2_len + il3_len + (il4_len >> 1);
+
 	if (!cfg_encap_proto)
-		return il3_len + il4_len + cfg_payload_len;
+		return l2_len + il3_len + il4_len + cfg_payload_len;
 
 	switch (cfg_l3_outer) {
 	case PF_INET:
-		build_ipv4_header(buf + el3_len, cfg_encap_proto,
+		build_ipv4_header(buf + l2_len + el3_len, cfg_encap_proto,
 				  out_saddr4.sin_addr.s_addr,
 				  out_daddr4.sin_addr.s_addr,
 				  ol4_len + il3_len + il4_len + cfg_payload_len,
 				  cfg_dsfield_outer);
 		break;
 	case PF_INET6:
-		build_ipv6_header(buf + el3_len, cfg_encap_proto,
+		build_ipv6_header(buf + l2_len + el3_len, cfg_encap_proto,
 				  &out_saddr6, &out_daddr6,
 				  ol4_len + il3_len + il4_len + cfg_payload_len,
 				  cfg_dsfield_outer);
@@ -350,17 +408,17 @@ static int build_packet(void)
 
 	switch (cfg_encap_proto) {
 	case IPPROTO_UDP:
-		build_gue_header(buf + el3_len + ol3_len + ol4_len -
+		build_gue_header(buf + l2_len + el3_len + ol3_len + ol4_len -
 				 sizeof(struct guehdr),
 				 cfg_l3_inner == PF_INET ? IPPROTO_IPIP
 							 : IPPROTO_IPV6);
-		build_udp_header(buf + el3_len + ol3_len,
+		build_udp_header(buf + l2_len + el3_len + ol3_len,
 				 sizeof(struct guehdr) + il3_len + il4_len +
 				 cfg_payload_len,
 				 cfg_port_gue, cfg_l3_outer);
 		break;
 	case IPPROTO_GRE:
-		build_gre_header(buf + el3_len + ol3_len,
+		build_gre_header(buf + l2_len + el3_len + ol3_len,
 				 cfg_l3_inner == PF_INET ? ETH_P_IP
 							 : ETH_P_IPV6);
 		break;
@@ -368,7 +426,7 @@ static int build_packet(void)
 
 	switch (cfg_l3_extra) {
 	case PF_INET:
-		build_ipv4_header(buf,
+		build_ipv4_header(buf + l2_len,
 				  cfg_l3_outer == PF_INET ? IPPROTO_IPIP
 							  : IPPROTO_IPV6,
 				  extra_saddr4.sin_addr.s_addr,
@@ -377,7 +435,7 @@ static int build_packet(void)
 				  cfg_payload_len, 0);
 		break;
 	case PF_INET6:
-		build_ipv6_header(buf,
+		build_ipv6_header(buf + l2_len,
 				  cfg_l3_outer == PF_INET ? IPPROTO_IPIP
 							  : IPPROTO_IPV6,
 				  &extra_saddr6, &extra_daddr6,
@@ -386,15 +444,46 @@ static int build_packet(void)
 		break;
 	}
 
-	return el3_len + ol3_len + ol4_len + il3_len + il4_len +
+	return l2_len + el3_len + ol3_len + ol4_len + il3_len + il4_len +
 	       cfg_payload_len;
 }
 
+static int setup_tx_pfpacket(void)
+{
+	struct sockaddr_ll laddr = {0};
+	const int one = 1;
+	uint16_t proto;
+	int fd;
+
+	fd = socket(PF_PACKET, SOCK_RAW, 0);
+	if (fd == -1)
+		error(1, errno, "socket tx");
+
+	if (cfg_use_vnet &&
+	    setsockopt(fd, SOL_PACKET, PACKET_VNET_HDR, &one, sizeof(one)))
+		error(1, errno, "setsockopt vnet");
+
+	proto = cfg_l3_inner == PF_INET ? ETH_P_IP : ETH_P_IPV6;
+	laddr.sll_family = AF_PACKET;
+	laddr.sll_protocol = htons(proto);
+	laddr.sll_ifindex = if_nametoindex("lo");
+	if (!laddr.sll_ifindex)
+		error(1, errno, "if_nametoindex");
+
+	if (bind(fd, (void *)&laddr, sizeof(laddr)))
+		error(1, errno, "bind");
+
+	return fd;
+}
+
 /* sender transmits encapsulated over RAW or unencap'd over UDP */
 static int setup_tx(void)
 {
 	int family, fd, ret;
 
+	if (cfg_tx_pf_packet)
+		return setup_tx_pfpacket();
+
 	if (cfg_l3_extra)
 		family = cfg_l3_extra;
 	else if (cfg_l3_outer)
@@ -464,6 +553,13 @@ static int do_tx(int fd, const char *pkt, int len)
 	int ret;
 
 	ret = write(fd, pkt, len);
+
+	if (cfg_expect_snd_failure) {
+		if (ret == -1)
+			return 0;
+		error(1, 0, "expected tx to fail but it did not");
+	}
+
 	if (ret == -1)
 		error(1, errno, "send");
 	if (ret != len)
@@ -571,7 +667,7 @@ static int do_main(void)
 	 * success (== 0) only if received all packets
 	 * unless failure is expected, in which case none must arrive.
 	 */
-	if (cfg_expect_failure)
+	if (cfg_expect_norx || cfg_expect_snd_failure)
 		return rx != 0;
 	else
 		return rx != tx;
@@ -623,8 +719,12 @@ static void parse_opts(int argc, char **argv)
 {
 	int c;
 
-	while ((c = getopt(argc, argv, "d:D:e:f:Fhi:l:n:o:O:Rs:S:t:Tx:X:")) != -1) {
+	while ((c = getopt(argc, argv,
+			   "cd:D:e:Ef:FGghi:l:Ln:o:O:pRs:S:t:TUvx:X:")) != -1) {
 		switch (c) {
+		case 'c':
+			cfg_vnet_use_csum_off = true;
+			break;
 		case 'd':
 			if (cfg_l3_outer == AF_UNSPEC)
 				error(1, 0, "-d must be preceded by -o");
@@ -653,11 +753,17 @@ static void parse_opts(int argc, char **argv)
 			else
 				usage(argv[0]);
 			break;
+		case 'E':
+			cfg_expect_snd_failure = true;
+			break;
 		case 'f':
 			cfg_src_port = strtol(optarg, NULL, 0);
 			break;
 		case 'F':
-			cfg_expect_failure = true;
+			cfg_expect_norx = true;
+			break;
+		case 'g':
+			cfg_vnet_use_gso = true;
 			break;
 		case 'h':
 			usage(argv[0]);
@@ -673,6 +779,9 @@ static void parse_opts(int argc, char **argv)
 		case 'l':
 			cfg_payload_len = strtol(optarg, NULL, 0);
 			break;
+		case 'L':
+			cfg_vnet_use_hdr_len_bad = true;
+			break;
 		case 'n':
 			cfg_num_pkt = strtol(optarg, NULL, 0);
 			break;
@@ -682,6 +791,9 @@ static void parse_opts(int argc, char **argv)
 		case 'O':
 			cfg_l3_extra = parse_protocol_family(argv[0], optarg);
 			break;
+		case 'p':
+			cfg_tx_pf_packet = true;
+			break;
 		case 'R':
 			cfg_only_rx = true;
 			break;
@@ -703,6 +815,12 @@ static void parse_opts(int argc, char **argv)
 		case 'T':
 			cfg_only_tx = true;
 			break;
+		case 'U':
+			cfg_partial_udp_hdr = true;
+			break;
+		case 'v':
+			cfg_use_vnet = true;
+			break;
 		case 'x':
 			cfg_dsfield_outer = strtol(optarg, NULL, 0);
 			break;
@@ -733,7 +851,26 @@ static void parse_opts(int argc, char **argv)
 	 */
 	if (((cfg_dsfield_outer & 0x3) == 0x3) &&
 	    ((cfg_dsfield_inner & 0x3) == 0x0))
-		cfg_expect_failure = true;
+		cfg_expect_norx = true;
+
+	/* Don't wait around for packets that we expect to fail to send */
+	if (cfg_expect_snd_failure && !cfg_num_secs)
+		cfg_num_secs = 3;
+
+	if (cfg_partial_udp_hdr && cfg_encap_proto)
+		error(1, 0,
+		      "ops: can't specify partial UDP hdr (-U) and encap (-e)");
+
+	if (cfg_use_vnet && cfg_encap_proto)
+		error(1, 0, "options: cannot specify encap (-e) with vnet (-v)");
+	if (cfg_use_vnet && !cfg_tx_pf_packet)
+		error(1, 0, "options: vnet (-v) requires psock for tx (-p)");
+	if (cfg_vnet_use_gso && !cfg_use_vnet)
+		error(1, 0, "options: gso (-g) requires vnet (-v)");
+	if (cfg_vnet_use_csum_off && !cfg_use_vnet)
+		error(1, 0, "options: vnet csum (-c) requires vnet (-v)");
+	if (cfg_vnet_use_hdr_len_bad && !cfg_use_vnet)
+		error(1, 0, "options: bad vnet hdrlen (-L) requires vnet (-v)");
 }
 
 static void print_opts(void)
diff --git a/tools/testing/selftests/bpf/test_flow_dissector.sh b/tools/testing/selftests/bpf/test_flow_dissector.sh
index 174b72a64a4c..5852cf815eeb 100755
--- a/tools/testing/selftests/bpf/test_flow_dissector.sh
+++ b/tools/testing/selftests/bpf/test_flow_dissector.sh
@@ -51,6 +51,9 @@ if [[ -z $(ip netns identify $$) ]]; then
 		echo "Skipping root flow dissector test, bpftool not found" >&2
 	fi
 
+	orig_flow_dissect_sysctl=$(</proc/sys/net/core/flow_dissect_vnet_hdr)
+	sysctl net.core.flow_dissect_vnet_hdr=1
+
 	# Run the rest of the tests in a net namespace.
 	../net/in_netns.sh "$0" "$@"
 	err=$(( $err + $? ))
@@ -61,6 +64,7 @@ if [[ -z $(ip netns identify $$) ]]; then
 		echo "selftests: $TESTNAME [FAILED]";
 	fi
 
+	sysctl net.core.flow_dissect_vnet_hdr=$orig_flow_dissect_sysctl
 	exit $err
 fi
 
@@ -165,4 +169,19 @@ tc filter add dev lo parent ffff: protocol ipv6 pref 1337 flower ip_proto \
 # Send 10 IPv6/UDP packets from port 10. Filter should not drop any.
 ./test_flow_dissector -i 6 -f 10
 
+
+echo "Testing virtio-net header validation..."
+echo "Testing valid vnet headers. Should *not* be dropped."
+./with_addr.sh ./test_flow_dissector -i 4 -D 192.168.0.1 -S 1.1.1.1 -p -v
+echo "Testing partial transport header. Should be dropped."
+./with_addr.sh ./test_flow_dissector -i 4 -D 192.168.0.1 -S 1.1.1.1 -p -v -U -E
+echo "Testing valid vnet gso spec. Should *not* be dropped."
+./with_addr.sh ./test_flow_dissector -i 4 -D 192.168.0.1 -S 1.1.1.1 -p -v -g -c -l 8000
+echo "Testing invalid vnet gso size. Should be dropped."
+./with_addr.sh ./test_flow_dissector -i 4 -D 192.168.0.1 -S 1.1.1.1 -p -v -g -c -l 100 -E
+echo "Testing invalid vnet header len. Should be dropped."
+./with_addr.sh ./test_flow_dissector -i 4 -D 192.168.0.1 -S 1.1.1.1 -p -v -L -E
+echo "Testing vnet gso without csum. Should be dropped."
+./with_addr.sh ./test_flow_dissector -i 4 -D 192.168.0.1 -S 1.1.1.1 -p -v -g -l 8000 -E
+
 exit 0
-- 
2.32.0.272.g935e593368-goog

Re: [PATCH net-next v5 1/3] net: flow_dissector: extend bpf flow dissector support with vnet hdr

[Martin KaFai Lau]

On Thu, Jun 10, 2021 at 02:38:51PM -0400, Tanner Love wrote:
[ ... ]

>  static int check_flow_keys_access(struct bpf_verifier_env *env, int off,
> -				  int size)
> +				  int size, enum bpf_access_type t)
>  {
>  	if (size < 0 || off < 0 ||
>  	    (u64)off + size > sizeof(struct bpf_flow_keys)) {
> @@ -3381,6 +3382,35 @@ static int check_flow_keys_access(struct bpf_verifier_env *env, int off,
>  			off, size);
>  		return -EACCES;
>  	}
> +
> +	switch (off) {
> +	case offsetof(struct bpf_flow_keys, vhdr):
It is not enough to stop writing to keys->vhdr.
e.g. what if off is offsetof(struct bpf_flow_keys, vhdr) + 1?

Will it break your existing use case if align access (off % size != 0) is
enforced now?  Take a look at bpf_skb_is_valid_access() in filter.c.
Otherwise, another way is needed here.

A nit. It is a good chance to move the new BTF_ID_LIST_SINGLE
and most of the check_flow_keys_access() to filter.c.
Take a look at check_sock_access().

> +		if (t == BPF_WRITE) {
> +			verbose(env,
> +				"invalid write to flow keys off=%d size=%d\n",
> +				off, size);
> +			return -EACCES;
> +		}
> +
> +		if (size != sizeof(__u64)) {
> +			verbose(env,
> +				"invalid access to flow keys off=%d size=%d\n",
> +				off, size);
> +			return -EACCES;
> +		}
> +
> +		break;
> +	case offsetof(struct bpf_flow_keys, vhdr_is_little_endian):
> +		if (t == BPF_WRITE) {
> +			verbose(env,
> +				"invalid write to flow keys off=%d size=%d\n",
> +				off, size);
> +			return -EACCES;
> +		}
> +
> +		break;
> +	}
> +
>  	return 0;
>  }
>  
> @@ -4053,6 +4083,8 @@ static int check_stack_access_within_bounds(
>  	return err;
>  }
>  
> +BTF_ID_LIST_SINGLE(bpf_flow_dissector_btf_ids, struct, virtio_net_hdr);
> +
>  /* check whether memory at (regno + off) is accessible for t = (read | write)
>   * if t==write, value_regno is a register which value is stored into memory
>   * if t==read, value_regno is a register which will receive the value from memory
> @@ -4217,9 +4249,19 @@ static int check_mem_access(struct bpf_verifier_env *env, int insn_idx, u32 regn
>  			return -EACCES;
>  		}
>  
> -		err = check_flow_keys_access(env, off, size);
> -		if (!err && t == BPF_READ && value_regno >= 0)
> -			mark_reg_unknown(env, regs, value_regno);
> +		err = check_flow_keys_access(env, off, size, t);
> +		if (!err && t == BPF_READ && value_regno >= 0) {
> +			if (off == offsetof(struct bpf_flow_keys, vhdr)) {
> +				mark_reg_known_zero(env, regs, value_regno);
> +				regs[value_regno].type = PTR_TO_BTF_ID_OR_NULL;
> +				regs[value_regno].btf = btf_vmlinux;
> +				regs[value_regno].btf_id = bpf_flow_dissector_btf_ids[0];
It needs to check "!bpf_flow_dissector_btf_ids[0]" in case
CONFIG_DEBUG_INFO_BTF is not enabled.  Take a look
at the RET_PTR_TO_BTF_ID case in verifier.c.

Re: [PATCH net-next v5 1/3] net: flow_dissector: extend bpf flow dissector support with vnet hdr

[Martin KaFai Lau]

On Fri, Jun 11, 2021 at 02:07:10PM -0700, Tanner Love wrote:
> > A nit. It is a good chance to move the new BTF_ID_LIST_SINGLE
> > and most of the check_flow_keys_access() to filter.c.
> > Take a look at check_sock_access().
> >
> 
> It's not clear to me why it's preferable to move most of the
> check_flow_keys_access() to filter.c. In particular, the part of
> your comment that I don't understand is the "most of" part. Why
> would we want to separate the flow-keys-access-checking logic
> into two separate functions? Thanks
Right, actually, the whole function can be moved.
I found it easier to follow from flow_dissector_is_valid_access()
to flow_keys's access check without jumping around between two
different files.

> 
> Additionally, it seems that we don't actually need the
> BTF_ID_LIST_SINGLE. Can we not, instead, set
> regs[value_regno].btf_id to
> btf_find_by_name_kind(btf_vmlinux, "virtio_net_hdr", BTF_KIND_STRUCT)
> ? (And we'll check that that value is not <= 0.)
BTF_ID_LIST_SINGLE is resolved during compilation.
btf_find_by_name_kind() will be repeatedly finding the btf_id during runtime.
It is not like a killer but still unnecessary.

Re: [PATCH net-next v5 1/3] net: flow_dissector: extend bpf flow dissector support with vnet hdr

[Martin KaFai Lau]

On Fri, Jun 11, 2021 at 06:13:42PM -0700, Martin KaFai Lau wrote:
> On Fri, Jun 11, 2021 at 02:07:10PM -0700, Tanner Love wrote:
> > > A nit. It is a good chance to move the new BTF_ID_LIST_SINGLE
> > > and most of the check_flow_keys_access() to filter.c.
> > > Take a look at check_sock_access().
> > >
> > 
> > It's not clear to me why it's preferable to move most of the
> > check_flow_keys_access() to filter.c. In particular, the part of
> > your comment that I don't understand is the "most of" part. Why
> > would we want to separate the flow-keys-access-checking logic
> > into two separate functions? Thanks
> Right, actually, the whole function can be moved.
> I found it easier to follow from flow_dissector_is_valid_access()
> to flow_keys's access check without jumping around between two
> different files.
The verifier verbose() logs can be kept in verifier.c though.  I
think all the -EACCES cases can be consolidated to one verbose()
call in check_mem_access() under PTR_TO_FLOW_KEYS.