mitigator_bpf.h File Reference

#include <stdbool.h>
#include <stddef.h>
#include <stdint.h>

Go to the source code of this file.

Data Structures
struct	EtherAddr
	Ethernet address (MAC address). More...
struct	EtherHeader
	Ethernet header (802.1). More...
struct	VlanHeader
	VLAN header (802.1q). More...
struct	IpHeader
	IPv4 header. More...
struct	Ip6Addr
	IPv6 address representation. More...
struct	Ip6Header
	IPv6 header. More...
struct	UdpHeader
	UDP header. More...
struct	TcpHeader
	TCP header. More...
struct	IcmpHeader
	ICMP and ICMPv6 header. More...
union	NetAddr
	Network address, either IPv4 or IPv6. More...
struct	Flow
	Packet flow information. More...
struct	TableRecord
	Record in the program-wide table. More...
struct	TableExResult
	Result of a lookup in the extended table. More...

Macros
#define	PROGRAM_DISPLAY_ID(id)
	Mandatory program identifier for display to the user. More...
#define	ENTRYPOINT
	Entry point function marker. More...
#define	LOCAL
	Force the compiler to inline a local function. More...
#define	PACKED
	Specify structure or union to be packed. More...
#define	UNROLL
	Hint the compiler to unroll a loop. More...
#define	MAX_PAYLOAD_LENGTH   1536
	Maximum length of any packet data returned by API functions. More...
#define	MAX_PARAMETERS_LENGTH   1024
	Maximum length of program parameters. More...
#define	TABLE_EX_KEY_SIZE   16
	Maximum allowed size of an extended table key.
#define	TABLE_EX_VALUE_SIZE   8
	Maximum size of an extended table record value.

Typedefs
typedef void *	Context
	Opaque filter context.
typedef uint64_t	Bool
	ABI-safe, EBPF-friendly boolean type. More...
typedef uint32_t	Time
typedef uint32_t	IpAddr
	IPv4 address.
typedef uint64_t	TableKey
typedef uint64_t	TableValue
typedef uint32_t	Cookie

Enumerations
enum	Result {   RESULT_PASS , RESULT_DROP , RESULT_BACK , RESULT_LIMIT ,   RESULT_SORB }
	Filter verdict. More...
enum	EtherType
	Ethernet frame type codes. More...
enum	IpProto
	IPv4 and IPv6 transport protocol codes. More...
enum	TcpFlags
	TCP flags. More...
enum	TcpOption
	TCP option codes. More...
enum	IcmpType
	ICMPv4 types.
enum	Icmp6Type
	ICMPv6 types.

Functions
const void *	parameters_get (Context ctx)
	Get a pointer to read-only program parameters. More...
void	packet_flow (Context ctx, struct Flow *info)
	Get packet flow information, including source and destination. More...
void *	packet_ether_header (Context ctx)
	Get packet Ethernet header. More...
uint16_t	packet_network_proto (Context ctx)
	Get packet network protocol code, e.g. IPv4. More...
void *	packet_network_header (Context ctx)
	Get packet network header, e.g. IPv4 header. More...
uint8_t	packet_transport_proto (Context ctx)
	Get packet transport protocol code, e.g. TCP, UDP, or ICMP. More...
void *	packet_transport_header (Context ctx)
	Get packet transport header, e.g. TCP header. More...
void *	packet_transport_payload (Context ctx, uint16_t *length)
	Get packet transport payload for TCP or UDP. More...
void	set_packet_length (Context ctx, uint16_t length)
	Set new packet transport payload length (max 1400). More...
void	set_packet_offset (Context ctx, uint16_t offset)
	Set number of bytes to strip from the beginning of transport payload. More...
void	set_packet_syncookie (Context ctx)
	Convert response packet to an empty TCP SYN+ACK with syncookie. More...
void	set_packet_mangled (Context ctx)
	Mark the packet as mangled by the program. More...
void	set_src_blacklisted (Context ctx, Time duration)
	Add packet source address to temporary blacklist. More...
void	set_src_whitelisted (Context ctx, Time duration)
	Add packet source address to temporary whitelist. More...
Bool	table_find (Context ctx, TableKey key, struct TableRecord *record)
	Lookup value in the basic table by key. More...
Bool	table_get (Context ctx, TableKey key, struct TableRecord *record)
	Lookup value in the basic table by key and modify record update time. More...
Bool	table_put (Context ctx, TableKey key, TableValue value)
	Update value in the basic table, creating a new record if needed. More...
uint64_t	table_size (Context ctx)
	Get number of records in the table.
struct TableExResult	table_ex_find (Context ctx, const void *key, const void *key_end, void *value, void *value_end)
	Lookup value in the extended table by key. More...
struct TableExResult	table_ex_get (Context ctx, const void *key, const void *key_end, void *value, void *value_end)
	Lookup value in the extended table by key and modify record update time. More...
Bool	table_ex_put (Context ctx, const void *key, const void *key_end, const void *value, const void *value_end)
	Update value in the extended table, creating a new record if needed. More...
uint64_t	table_ex_size (Context ctx)
	Get number of records in the extended table.
Cookie	cookie_make (Context ctx, const struct Flow *id)
	Make a generic cookie value based on random seed, current time, and flow fields that identify the client. More...
Bool	cookie_check (Context ctx, const struct Flow *id, Cookie cookie)
	Check if a generic cookie matches the flow and has not expired. More...
Cookie	syncookie_make (Context ctx)
	Make a cookie value for use as a sequence number in a SYN+ACK packet. More...
Bool	syncookie_check (Context ctx, uint32_t seqnum_offset, uint32_t acknum_offset)
	Check if packet is a TCP ACK carrying a SYN cookie. More...
void	set_packet_isn_syncookie (Context ctx)
	Convert response packet to an empty TCP SYN+ACK with ISN syncookie. More...
Bool	isn_syncookie_check (Context ctx, uint32_t seqnum_offset, uint32_t acknum_offset)
	Check if packet is a TCP ACK carrying an ISN SYN cookie. More...
void	isn_send_ack_packet (Context ctx)
	Send ACK packet with ISN syncookie. More...
Bool	bloom_check (Context ctx, uint64_t hash)
	Check if hash value is stored in the bloom filter. More...
void	bloom_add (Context ctx, uint64_t hash)
	Add hash value to the bloom filter.
void	bloom_reset (Context ctx)
	Reset bloom filter to the initial state.
uint32_t	hash_crc32_u32 (uint32_t value, uint32_t init)
	Compute CRC32 (Castagnoli) of a 32-bit value. More...
uint32_t	hash_crc32_u64 (uint64_t value, uint32_t init)
	Compute CRC32 (Castagnoli) of a 64-bit value. More...
uint32_t	hash_crc32_data (const void *data, const void *end, uint32_t init)
	Compute CRC32 (Castagnoli) over [data; end). More...
uint64_t	rand64 (void)
	Generate a pseudo-random, non cryptographically-secure value.
Time	time_sec (Context ctx)
	Get system time in seconds.
LOCAL uint16_t	bswap16 (uint16_t value)
	Change byte order of a 16-bit value.
LOCAL uint32_t	bswap32 (uint32_t value)
	Change byte order of a 32-bit value.
LOCAL uint64_t	bswap64 (uint64_t value)
	Change byte order of a 64-bit value.
LOCAL uint16_t	vlan_get_id (const struct VlanHeader *vlan)
	Get VLAN ID from 802.1q header.
LOCAL void	vlan_set_id (struct VlanHeader *vlan, uint16_t id)
	Set VLAN ID in 802.1q header. More...

Macro Definition Documentation

ENTRYPOINT

#define ENTRYPOINT

Entry point function marker.

A filter that drops all packets looks as follows:

#include "mitigator_bpf.h"
 
ENTRYPOINT enum Result
filter(Context ctx) {
    return RESULT_DROP;
}
 
PROGRAM_DISPLAY_ID("Example v0.1")

LOCAL

#define LOCAL

Force the compiler to inline a local function.

This macro should be used on all function definitions, otherwise compiler might generate code that will fail verification (which forbids backward jumps).

Example:

LOCAL int
sum(int a, int b) {
    return a + b;
}

MAX_PARAMETERS_LENGTH

#define MAX_PARAMETERS_LENGTH   1024

Maximum length of program parameters.

Before using a variable offset into parameters, a program must check that it does not exceed this constant.

See also

MAX_PAYLOAD_LENGTH for comments on offset checking.

parameters_get() to get parameters.

MAX_PAYLOAD_LENGTH

#define MAX_PAYLOAD_LENGTH   1536

Maximum length of any packet data returned by API functions.

Before using a variable offset into packet, a program must check that it does not exceed this constant, otherwise EBPF verifier may reject the code. To avoid valid programs being mistakenly rejected, place the check immediately before using the offset.

See also

hash_crc32_data() for example usage.

PACKED

#define PACKED

Specify structure or union to be packed.

Example:

struct PACKED Packed {
    uint16_t a;
    uint32_t b;
    uint8_t c;
}

PROGRAM_DISPLAY_ID

#define PROGRAM_DISPLAY_ID

(

id

)

Mandatory program identifier for display to the user.

The system may reject programs without this identifier.

The string should help the user to identify program and its version. It can be truncated on display, guaranteed minimum is 40 characters.

See also

FILTER_V1 for usage example.

UNROLL

#define UNROLL

Hint the compiler to unroll a loop.

Loops are usually translated to the following instruction sequence: condition check, loop body, backwards jump to condition check. EBPF verifier forbids backwards jumps to prevent infinite loops. Loop unrolling means loop body will be pasted a fixed number of times in generated code.

Obviously, unrolling requires knowledge of maximum iteration count in advance, thus the code to loop "n" times is as follows:

UNROLL for (i = 0; i < MAX; i++) {
    if (i >= n) {
        break;
    }
    ...
}

Note

This macro currently only affects Clang.

The hint might be ignored, especially with optimizations disabled.

Typedef Documentation

Bool

typedef uint64_t Bool

ABI-safe, EBPF-friendly boolean type.

Definitions of true and false from <stdbool.h> can be used with Bool.

Cookie

typedef uint32_t Cookie

Cookie value.

TableKey

typedef uint64_t TableKey

Key to a record in the program-wide basic table.

Key 0 is reserved. It is forbidden to save values by key 0 and records are never found by this key.

See also

TableRecord for table description.

TableValue

typedef uint64_t TableValue

Value of a record in the program-wide basic table.

See also

TableRecord for table description.

Time

typedef uint32_t Time

Time in seconds: Unix timestamp or duration.

See also

time_sec() to get current time.

Enumeration Type Documentation

EtherType

enum EtherType

Ethernet frame type codes.

See also

packet_network_proto() for an example use of these values.

IpProto

enum IpProto

IPv4 and IPv6 transport protocol codes.

See also

packet_transport_proto() for an example use of these values.

https://www.iana.org/assignments/protocol-numbers/protocol-numbers.xhtml

Result

enum Result

Filter verdict.

Program return values.

Enumerator
RESULT_PASS	Pass packet (forward).
RESULT_DROP	Drop packet (discard).
RESULT_BACK	Send packet back. L2, L3, and L4 headers are adjusted automatically.
RESULT_LIMIT	Pass packet if overall rate is within limit, otherwise drop packet.
RESULT_SORB	Pass packet if overall rate from its source address is within limit. Otherwise, drop packet and optionally block future packets from its source address.

TcpFlags

enum TcpFlags

TCP flags.

Combinations of these flags are used for TcpHeader::th_flags.

URG, ECE, and CWR may be combined with any other flags, and PUSH is often combined with ACK, but is never mandatory. So this is the wrong way to check for ACK segments:

if (tcp->th_flags == TCP_FLAG_ACK) {
    // WRONG: will not run for ACK+PUSH, which is very common
}

To check if ACK flag is present in a combination:

if (tcp->th_flags & TCP_FLAG_ACK) { ... }

To switch on the flags:

switch (tcp->th_flags & (TCP_FLAG_SYN | TCP_FLAG_ACK)) {
case TCP_FLAG_SYN: ...; break;
case TCP_FLAG_ACK: ...; break;
case TCP_FLAG_SYN | TCP_FLAG_ACK: ...; break;
}

TcpOption

enum TcpOption

TCP option codes.

Options start immediately after TCP header and are limited to 44 bytes, so a loop over them may be UNROLL'ed. Options must be padded to 4 bytes.

See also

https://www.iana.org/assignments/tcp-parameters/tcp-parameters.xhtml#tcp-parameters-1

Function Documentation

bloom_check()

Bool bloom_check	(	Context	ctx,
		uint64_t	hash
	)

Check if hash value is stored in the bloom filter.

False positive matches are possible, but false negatives are not.

cookie_check()

Bool cookie_check	(	Context	ctx,
		const struct Flow *	id,
		Cookie	cookie
	)

Check if a generic cookie matches the flow and has not expired.

This function checks is the cookie was generated by cookie_make() recently with the same exact flow.

See also

cookie_make for comments on filling the Flow structure.

The following code checks for a cookie in the beginning of payload:

uint16_t length = 0;
uint32_t* cookie = packet_transport_payload(ctx, &length);
 
struct Flow flow;
packet_flow(ctx, &flow);
 
flow.src_port = 0;
if (cookie_check(ctx, &flow, *cookie) {
    ...
}

cookie_make()

Cookie cookie_make	(	Context	ctx,
		const struct Flow *	id
	)

Make a generic cookie value based on random seed, current time, and flow fields that identify the client.

Use cookie_check() to check the cookie returned in response.

Zero unneeded flow fields of to ignore them, e.g. zero source port if clients are likely to change it when sending response. Always make sure struct Flow padding is zero (packet_flow() does this automatically).

The following code puts a cookie in the beginning of the response:

uint16_t length = 0;
uint32_t* cookie = packet_transport_payload(ctx, &length);
 
struct Flow flow;
packet_flow(ctx, &flow);
 
flow.src_port = 0;
*cookie = cookie_make(ctx, &flow);
set_packet_length(ctx, sizeof(*cookie));
return RESULT_BACK;

hash_crc32_data()

uint32_t hash_crc32_data	(	const void *	data,
		const void *	end,
		uint32_t	init
	)

Compute CRC32 (Castagnoli) over [data; end).

Suppose a protocol requires first four bytes of payload to be CRC32 of the remaining payload, using initial value 0xFFFFFFFF. A filter can verify packets as follows:

static const uint32_t INIT = 0xFFFFFFFF;
 
uint16_t length = 0;
uint8_t* payload = packet_transport_payload(ctx, &length);
uint32_t crc = *(uint32_t*)payload;
uint8_t* rest = payload + sizeof(crc);
uint8_t* rest_end = payload + length;
 
if (length > MAX_PAYLOAD_LENGTH) {
    // Never happens, but required to validate that rest_end
    // does not point beyond packet data.
    return RESULT_DROP;
}
 
if (hash_crc32_data(rest, rest_end, INIT) == crc) {
    return RESULT_PASS;
}

See also

MAX_PAYLOAD_LENGTH for detailed explanation why it's checked.

hash_crc32_u32() for a simpler alternative for 32-bit data.

hash_crc32_u64() for a simpler alternative for 64-bit data.

hash_crc32_u32()

uint32_t hash_crc32_u32	(	uint32_t	value,
		uint32_t	init
	)

Compute CRC32 (Castagnoli) of a 32-bit value.

Note that crc32(A concatenated with B, init) == crc32(B, crc32(A, init)). For example, the following code computes CRC32 of a seed concatenated with source IP (initial value 0x814141AB does not matter).

struct Flow flow;
packet_flow(ctx, &flow);
uint32_t crc = hash_crc32_u32(flow.src, hash_crc32_u32(seed), 0x814141AB);

See also

hash_crc32_data() for dynamically-sized data.

hash_crc32_u64()

uint32_t hash_crc32_u64	(	uint64_t	value,
		uint32_t	init
	)

Compute CRC32 (Castagnoli) of a 64-bit value.

See also

hash_crc32_u32() for additional notes and examples.

isn_send_ack_packet()

void isn_send_ack_packet

(

Context

ctx

)

Send ACK packet with ISN syncookie.

Must be called to send empty ACK packet with correct ISN syncooke to open TCP connection on the protected host.

isn_syncookie_check()

Bool isn_syncookie_check	(	Context	ctx,
		uint32_t	seqnum_offset,
		uint32_t	acknum_offset
	)

Check if packet is a TCP ACK carrying an ISN SYN cookie.

Note

ISN is supported only for IPv4 policy context.

packet_ether_header()

void * packet_ether_header

(

Context

ctx

)

Get packet Ethernet header.

Programs may access up to MAX_LAYLOAD_LENGTH bytes starting from this header, so that VLAN tags, encapsulation, etc. can be processed. However, data always starts with a struct EtherHeader.

Note

Restricted to General Protection.

Do not assume network layer header starts after Ethernet header: VLAN header may be there; use packet_network_header() instead.

packet_flow()

void packet_flow	(	Context	ctx,
		struct Flow *	info
	)

Get packet flow information, including source and destination.

This is simpler and more efficient than analysing L3 and L4 headers. Unused bytes, e.g. in IPv6 addresses for IPv4 packet, are zero-filled.

packet_network_header()

void * packet_network_header

(

Context

ctx

)

Get packet network header, e.g. IPv4 header.

Programs may access up to MAX_PAYLOAD_LENGTH bytes starting from the header, so that variable-length IP options and/or encapsulation headers can be processed. However, usually casting to a fixed-length header, e.g. IpHeader, is sufficient.

Note

This function always succeeds. Use packet_network_proto() to check if expected header is present.

If you only need addresses, consider using packet_flow().

See also

IpHeader

Ip6Header

packet_network_proto()

uint16_t packet_network_proto

(

Context

ctx

)

Get packet network protocol code, e.g. IPv4.

Return values are in host byte order:

if (packet_network_proto(packet) == ETHER_TYPE_IP) { ... }

See also

EtherType

packet_transport_header()

void * packet_transport_header

(

Context

ctx

)

Get packet transport header, e.g. TCP header.

Programs may access up to MAX_PAYLOAD_LENGTH bytes starting from the header, so that variable-length TCP options and/or encapsulation headers can be processed. However, usually casting to a fixed-length TcpHeader or UdpHeader is sufficient.

Note

This function always succeeds. Use packet_transport_proto() to check if expected header is present.

If you only need ports, consider using packet_flow().

See also

TcpHeader

UdpHeader

packet_transport_payload()

void * packet_transport_payload	(	Context	ctx,
		uint16_t *	length
	)

Get packet transport payload for TCP or UDP.

For protocols other than TCP and UDP, data starting from L4 header is returned. Use packet_transport_proto() to check the protocol.

Example:

uint16_t length = 0;
uint8_t* payload = packet_transport_payload(ctx, &length);

packet_transport_proto()

uint8_t packet_transport_proto

(

Context

ctx

)

Get packet transport protocol code, e.g. TCP, UDP, or ICMP.

Use IpProto constants to match on return value as follows:

if (packet_transport_proto(ctx) == IP_PROTO_TCP) { ... }

parameters_get()

const void * parameters_get

(

Context

ctx

)

Get a pointer to read-only program parameters.

Programs typically use parameters to allow keys, seeds, and thresholds to be configurable by user without recompiling the source. The entire space of MAX_PARAMETERS_LENGTH bytes is always available to the program. Bytes not supplied by user are zero-filled.

set_packet_isn_syncookie()

void set_packet_isn_syncookie

(

Context

ctx

)

Convert response packet to an empty TCP SYN+ACK with ISN syncookie.

Note

Packet is marked as mangled and its headers are updated automatically.

This function takes effect after the filter has finished.

This function only takes effect when the filter returns RESULT_BACK.

ISN is supported only for IPv4 policy context.

set_packet_length()

void set_packet_length	(	Context	ctx,
		uint16_t	length
	)

Set new packet transport payload length (max 1400).

Note

Packet is marked as mangled and its headers are updated automatically.

This function takes effect after the filter has finished.

set_packet_mangled()

void set_packet_mangled

(

Context

ctx

)

Mark the packet as mangled by the program.

A call to this function is required when changes are made directly to the packet headers or data using pointers and the filter returns RESULT_PASS. If the filter returns RESULT_BACK, packet is always mangled. If the filter returns RESULT_DROP, mangling is meaningless.

Note

Changes to length fields of network and transport headers will not be picked up by this function, use set_packet_length(), otherwise the packet will be malformed.

This function takes effect after the filter has finished.

set_packet_offset()

void set_packet_offset	(	Context	ctx,
		uint16_t	offset
	)

Set number of bytes to strip from the beginning of transport payload.

Note

If you use this function, you must also call set_packet_length() to set up the length for the rest of the packet, otherwise it will be truncated, i.e. its length set to 0.

Packet is marked as mangled and its headers are updated automatically.

This function takes effect after the filter has finished.

set_packet_syncookie()

void set_packet_syncookie

(

Context

ctx

)

Convert response packet to an empty TCP SYN+ACK with syncookie.

TCP sequence number is set to a cookie value recognized by syncookie_check(). IPv4 "don't fragment" flag is always set, TCP options are kept intact.

Note

Packet is marked as mangled and its headers are updated automatically.

This function takes effect after the filter has finished.

This function only takes effect when the filter returns RESULT_BACK.

set_src_blacklisted()

void set_src_blacklisted	(	Context	ctx,
		Time	duration
	)

Add packet source address to temporary blacklist.

Note

This function only works for IPv4.

This function overrides effect of set_src_whitelisted().

set_src_whitelisted()

void set_src_whitelisted	(	Context	ctx,
		Time	duration
	)

Add packet source address to temporary whitelist.

Note

This function only works for IPv4.

This function overrides effect of set_src_blacklisted().

syncookie_check()

Bool syncookie_check	(	Context	ctx,
		uint32_t	seqnum_offset,
		uint32_t	acknum_offset
	)

Check if packet is a TCP ACK carrying a SYN cookie.

This function checks if packet's TCP acknowledgement number matches the one generated by syncookie_make() or set_packet_syncookie() recently. It fails non-TCP packets.

This function can be used not only to implement SYN cookie protection, but also to recognize first data packets in a TCP session. For example, if seqnum_offset is 0, the first chunk of data is recognized. To recognize data starting from the 10-th octet, set seqnum_offset to 10. Likewise, set acknum_offset to 20 to recognize a packet acknowledging 20 first octets sent back to the client.

syncookie_make()

Cookie syncookie_make

(

Context

ctx

)

Make a cookie value for use as a sequence number in a SYN+ACK packet.

Values generated by this function are recognized by syncookie_check(). This function is for custom processing of TCP handshake.

Note

Use set_packet_syncookie() instead to avoid dealing with TCP header.

table_ex_find()

struct TableExResult table_ex_find	(	Context	ctx,
		const void *	key,
		const void *	key_end,
		void *	value,
		void *	value_end
	)

Lookup value in the extended table by key.

Buffer from key to key_end must not exceed TABLE_EX_KEY_SIZE bytes. Buffer from value to value_end must not exceed TABLE_EX_VALUE_SIZE bytes.

Note

Prefer table_ex_get() if any found record must also be kept in the table.

table_ex_get()

struct TableExResult table_ex_get	(	Context	ctx,
		const void *	key,
		const void *	key_end,
		void *	value,
		void *	value_end
	)

Lookup value in the extended table by key and modify record update time.

Result holds previous update time, which can be used to measure time elapsed since last table_ex_get() call on the record.

See also

table_ex_find() for parameter description.

table_ex_put()

Bool table_ex_put	(	Context	ctx,
		const void *	key,
		const void *	key_end,
		const void *	value,
		const void *	value_end
	)

Update value in the extended table, creating a new record if needed.

If key is not found and new record cannot be created, return false, otherwise return true.

Note

This function modifies record update time even if the value does not change.

See also

table_ex_find() for parameter description.

table_find()

Bool table_find	(	Context	ctx,
		TableKey	key,
		struct TableRecord *	record
	)

Lookup value in the basic table by key.

Note

Prefer table_get() if any found record must also be kept in the table.

table_get()

Bool table_get	(	Context	ctx,
		TableKey	key,
		struct TableRecord *	record
	)

Lookup value in the basic table by key and modify record update time.

Returned table record holds previous update time, which can be used to measure time elapsed since last table_get() or table_put() call on the record.

table_put()

Bool table_put	(	Context	ctx,
		TableKey	key,
		TableValue	value
	)

Update value in the basic table, creating a new record if needed.

If key is not found and new record cannot be created, return false, otherwise return true.

Note

This function modifies record update time even if the value does not change.

vlan_set_id()

LOCAL void vlan_set_id	(	struct VlanHeader *	vlan,
		uint16_t	id
	)

Set VLAN ID in 802.1q header.

If you don't need to keep rarely used DEI and PRI, a faster alternative is:

vlan->control = bswap16(id);