ssl_pkt.h

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/*
 *  OpenVPN -- An application to securely tunnel IP networks
 *             over a single TCP/UDP port, with support for SSL/TLS-based
 *             session authentication and key exchange,
 *             packet encryption, packet authentication, and
 *             packet compression.
 *
 *  Copyright (C) 2002-2025 OpenVPN Inc <sales@openvpn.net>
 *
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License version 2
 *  as published by the Free Software Foundation.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License along
 *  with this program; if not, see <https://www.gnu.org/licenses/>.
 */
 
#ifndef SSL_PKT_H
#define SSL_PKT_H
 
#include "buffer.h"
#include "ssl_backend.h"
#include "ssl_common.h"
 
/* packet opcode (high 5 bits) and key-id (low 3 bits) are combined in one byte */
#define P_KEY_ID_MASK  0x07
#define P_OPCODE_SHIFT 3
 
/* packet opcodes -- the V1 is intended to allow protocol changes in the future */
#define P_CONTROL_HARD_RESET_CLIENT_V1 1 /* initial key from client, forget previous state */
#define P_CONTROL_HARD_RESET_SERVER_V1 2 /* initial key from server, forget previous state */
#define P_CONTROL_SOFT_RESET_V1        3 /* new key, graceful transition from old to new key */
#define P_CONTROL_V1                   4 /* control channel packet (usually TLS ciphertext) */
#define P_ACK_V1                       5 /* acknowledgement for packets received */
#define P_DATA_V1                      6 /* data channel packet */
#define P_DATA_V2                      9 /* data channel packet with peer-id */
 
/* indicates key_method >= 2 */
#define P_CONTROL_HARD_RESET_CLIENT_V2 7 /* initial key from client, forget previous state */
#define P_CONTROL_HARD_RESET_SERVER_V2 8 /* initial key from server, forget previous state */
 
/* indicates key_method >= 2 and client-specific tls-crypt key */
#define P_CONTROL_HARD_RESET_CLIENT_V3 10 /* initial key from client, forget previous state */
 
/* Variant of P_CONTROL_V1 but with appended wrapped key
 * like P_CONTROL_HARD_RESET_CLIENT_V3 */
#define P_CONTROL_WKC_V1 11
 
/* define the range of legal opcodes
 * Since we do no longer support key-method 1 we consider
 * the v1 op codes invalid */
#define P_FIRST_OPCODE 3
#define P_LAST_OPCODE  11
 
/*
 * Define number of buffers for send and receive in the reliability layer.
 */
#define TLS_RELIABLE_N_SEND_BUFFERS 6 /* also window size for reliability layer */
#define TLS_RELIABLE_N_REC_BUFFERS  12
 
/*
 * Used in --mode server mode to check tls-auth signature on initial
 * packets received from new clients.
 */
struct tls_auth_standalone
{
    struct tls_wrap_ctx tls_wrap;
    struct buffer workbuf;
    struct frame frame;
};
 
enum first_packet_verdict
{
    VERDICT_VALID_RESET_V2,
    VERDICT_VALID_RESET_V3,
    VERDICT_VALID_CONTROL_V1,
    VERDICT_VALID_ACK_V1,
    VERDICT_VALID_WKC_V1,
    VERDICT_INVALID
};
 
struct tls_pre_decrypt_state
{
    struct tls_wrap_ctx tls_wrap_tmp;
    struct buffer newbuf;
    struct session_id peer_session_id;
    struct session_id server_session_id;
};
 
void free_tls_pre_decrypt_state(struct tls_pre_decrypt_state *state);
 
enum first_packet_verdict tls_pre_decrypt_lite(const struct tls_auth_standalone *tas,
                                               struct tls_pre_decrypt_state *state,
                                               const struct link_socket_actual *from,
                                               const struct buffer *buf);
 
/* Creates an SHA256 HMAC context with a random key that is used for the
 * session id.
 *
 * We do not support loading this from a config file since continuing session
 * between restarts of OpenVPN has never been supported and that includes
 * early session setup.
 */
hmac_ctx_t *session_id_hmac_init(void);
 
struct session_id calculate_session_id_hmac(struct session_id client_sid,
                                            const struct openvpn_sockaddr *from, hmac_ctx_t *hmac,
                                            int handwindow, int offset);
 
bool check_session_hmac_and_pkt_id(struct tls_pre_decrypt_state *state, const struct openvpn_sockaddr *from,
                                   hmac_ctx_t *hmac, int handwindow, bool pkt_is_ack);
 
/*
 * Write a control channel authentication record.
 */
void write_control_auth(struct tls_session *session, struct key_state *ks, struct buffer *buf,
                        struct link_socket_actual **to_link_addr, int opcode, int max_ack,
                        bool prepend_ack);
 
 
bool read_control_auth(struct buffer *buf, struct tls_wrap_ctx *ctx,
                       const struct link_socket_actual *from, const struct tls_options *opt,
                       bool initial_packet);
 
 
struct buffer tls_reset_standalone(struct tls_wrap_ctx *ctx, struct tls_auth_standalone *tas,
                                   struct session_id *own_sid, struct session_id *remote_sid,
                                   uint8_t header, bool request_resend_wkc);
 
 
struct buffer extract_command_buffer(struct buffer *buf, struct gc_arena *gc);
 
static inline const char *
packet_opcode_name(int op)
{
    switch (op)
    {
        case P_CONTROL_HARD_RESET_CLIENT_V1:
            return "P_CONTROL_HARD_RESET_CLIENT_V1";
 
        case P_CONTROL_HARD_RESET_SERVER_V1:
            return "P_CONTROL_HARD_RESET_SERVER_V1";
 
        case P_CONTROL_HARD_RESET_CLIENT_V2:
            return "P_CONTROL_HARD_RESET_CLIENT_V2";
 
        case P_CONTROL_HARD_RESET_SERVER_V2:
            return "P_CONTROL_HARD_RESET_SERVER_V2";
 
        case P_CONTROL_HARD_RESET_CLIENT_V3:
            return "P_CONTROL_HARD_RESET_CLIENT_V3";
 
        case P_CONTROL_SOFT_RESET_V1:
            return "P_CONTROL_SOFT_RESET_V1";
 
        case P_CONTROL_V1:
            return "P_CONTROL_V1";
 
        case P_CONTROL_WKC_V1:
            return "P_CONTROL_WKC_V1";
 
        case P_ACK_V1:
            return "P_ACK_V1";
 
        case P_DATA_V1:
            return "P_DATA_V1";
 
        case P_DATA_V2:
            return "P_DATA_V2";
 
        default:
            return "P_???";
    }
}
 
static inline struct tls_wrap_ctx *
tls_session_get_tls_wrap(struct tls_session *session, int key_id)
{
    /* OpenVPN has the hardcoded assumption in its protocol that
     * key-id 0 is always first session and renegotiations use key-id
     * 1 to 7 and wrap around to 1 after that. So key-id > 0 is equivalent
     * to "this is a renegotiation"
     */
    if (key_id > 0 && session->tls_wrap_reneg.mode == TLS_WRAP_CRYPT)
    {
        return &session->tls_wrap_reneg;
    }
    else
    {
        return &session->tls_wrap;
    }
}
 
/* initial packet id (instead of 0) that indicates that the peer supports
 * early protocol negotiation. This will make the packet id turn a bit faster
 * but the network time part of the packet id takes care of that. And
 * this is also a rather theoretical scenario as it still needs more than
 * 2^31 control channel packets to happen */
#define EARLY_NEG_MASK  0xff000000
#define EARLY_NEG_START 0x0f000000
 
 
/* Early negotiation that part of the server response in the RESET_V2 packet.
 * Since clients that announce early negotiation support will treat the payload
 * of reset packets special and parse it as TLV messages.
 * as TLV (type, length, value) */
#define TLV_TYPE_EARLY_NEG_FLAGS  0x0001
#define EARLY_NEG_FLAG_RESEND_WKC 0x0001
#endif /* ifndef SSL_PKT_H */