libsmb/smb_signing.c

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/* 
   Unix SMB/CIFS implementation.
   SMB Signing Code
   Copyright (C) Jeremy Allison 2003.
   Copyright (C) Andrew Bartlett <abartlet@samba.org> 2002-2003
   
   This program is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2 of the License, or
   (at your option) any later version.
   
   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, write to the Free Software
   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
*/

#include "includes.h"

/* Lookup a packet's MID (multiplex id) and figure out it's sequence number */
struct outstanding_packet_lookup {
        struct outstanding_packet_lookup *prev, *next;
        uint16 mid;
        uint32 reply_seq_num;
        BOOL can_delete; /* Set to False in trans state. */
};

struct smb_basic_signing_context {
        DATA_BLOB mac_key;
        uint32 send_seq_num;
        struct outstanding_packet_lookup *outstanding_packet_list;
};

static BOOL store_sequence_for_reply(struct outstanding_packet_lookup **list, 
                                     uint16 mid, uint32 reply_seq_num)
{
        struct outstanding_packet_lookup *t;

        /* Ensure we only add a mid once. */
        for (t = *list; t; t = t->next) {
                if (t->mid == mid) {
                        return False;
                }
        }

        t = SMB_XMALLOC_P(struct outstanding_packet_lookup);
        ZERO_STRUCTP(t);

        t->mid = mid;
        t->reply_seq_num = reply_seq_num;
        t->can_delete = True;

        /*
         * Add to the *start* of the list not the end of the list.
         * This ensures that the *last* send sequence with this mid
         * is returned by preference.
         * This can happen if the mid wraps and one of the early
         * mid numbers didn't get a reply and is still lurking on
         * the list. JRA. Found by Fran Fabrizio <fran@cis.uab.edu>.
         */

        DLIST_ADD(*list, t);
        DEBUG(10,("store_sequence_for_reply: stored seq = %u mid = %u\n",
                        (unsigned int)reply_seq_num, (unsigned int)mid ));
        return True;
}

static BOOL get_sequence_for_reply(struct outstanding_packet_lookup **list,
                                   uint16 mid, uint32 *reply_seq_num)
{
        struct outstanding_packet_lookup *t;

        for (t = *list; t; t = t->next) {
                if (t->mid == mid) {
                        *reply_seq_num = t->reply_seq_num;
                        DEBUG(10,("get_sequence_for_reply: found seq = %u mid = %u\n",
                                (unsigned int)t->reply_seq_num, (unsigned int)t->mid ));
                        if (t->can_delete) {
                                DLIST_REMOVE(*list, t);
                                SAFE_FREE(t);
                        }
                        return True;
                }
        }
        return False;
}

static BOOL set_sequence_can_delete_flag(struct outstanding_packet_lookup **list, uint16 mid, BOOL can_delete_entry)
{
        struct outstanding_packet_lookup *t;

        for (t = *list; t; t = t->next) {
                if (t->mid == mid) {
                        t->can_delete = can_delete_entry;
                        return True;
                }
        }
        return False;
}

/***********************************************************
 SMB signing - Common code before we set a new signing implementation
************************************************************/

static BOOL cli_set_smb_signing_common(struct cli_state *cli) 
{
        if (!cli->sign_info.allow_smb_signing) {
                return False;
        }

        if (!cli->sign_info.negotiated_smb_signing 
            && !cli->sign_info.mandatory_signing) {
                return False;
        }

        if (cli->sign_info.doing_signing) {
                return False;
        }
        
        if (cli->sign_info.free_signing_context)
                cli->sign_info.free_signing_context(&cli->sign_info);

        /* These calls are INCOMPATIBLE with SMB signing */
        cli->readbraw_supported = False;
        cli->writebraw_supported = False;
        
        return True;
}

/***********************************************************
 SMB signing - Common code for 'real' implementations
************************************************************/

static BOOL set_smb_signing_real_common(struct smb_sign_info *si)
{
        if (si->mandatory_signing) {
                DEBUG(5, ("Mandatory SMB signing enabled!\n"));
        }

        si->doing_signing = True;
        DEBUG(5, ("SMB signing enabled!\n"));

        return True;
}

static void mark_packet_signed(char *outbuf)
{
        uint16 flags2;
        flags2 = SVAL(outbuf,smb_flg2);
        flags2 |= FLAGS2_SMB_SECURITY_SIGNATURES;
        SSVAL(outbuf,smb_flg2, flags2);
}

/***********************************************************
 SMB signing - NULL implementation - calculate a MAC to send.
************************************************************/

static void null_sign_outgoing_message(char *outbuf, struct smb_sign_info *si)
{
        /* we can't zero out the sig, as we might be trying to send a
           session request - which is NBT-level, not SMB level and doesn't
           have the field */
        return;
}

/***********************************************************
 SMB signing - NULL implementation - check a MAC sent by server.
************************************************************/

static BOOL null_check_incoming_message(char *inbuf, struct smb_sign_info *si, BOOL must_be_ok)
{
        return True;
}

/***********************************************************
 SMB signing - NULL implementation - free signing context
************************************************************/

static void null_free_signing_context(struct smb_sign_info *si)
{
        return;
}

/**
 SMB signing - NULL implementation - setup the MAC key.

 @note Used as an initialisation only - it will not correctly
       shut down a real signing mechanism
*/

static BOOL null_set_signing(struct smb_sign_info *si)
{
        si->signing_context = NULL;
        
        si->sign_outgoing_message = null_sign_outgoing_message;
        si->check_incoming_message = null_check_incoming_message;
        si->free_signing_context = null_free_signing_context;

        return True;
}

/**
 * Free the signing context
 */
 
static void free_signing_context(struct smb_sign_info *si)
{
        if (si->free_signing_context) {
                si->free_signing_context(si);
                si->signing_context = NULL;
        }

        null_set_signing(si);
}


static BOOL signing_good(char *inbuf, struct smb_sign_info *si, BOOL good, uint32 seq, BOOL must_be_ok) 
{
        if (good) {

                if (!si->doing_signing) {
                        si->doing_signing = True;
                }
                
                if (!si->seen_valid) {
                        si->seen_valid = True;
                }

        } else {
                if (!si->mandatory_signing && !si->seen_valid) {

                        if (!must_be_ok) {
                                return True;
                        }
                        /* Non-mandatory signing - just turn off if this is the first bad packet.. */
                        DEBUG(5, ("srv_check_incoming_message: signing negotiated but not required and peer\n"
                                  "isn't sending correct signatures. Turning off.\n"));
                        si->negotiated_smb_signing = False;
                        si->allow_smb_signing = False;
                        si->doing_signing = False;
                        free_signing_context(si);
                        return True;
                } else if (!must_be_ok) {
                        /* This packet is known to be unsigned */
                        return True;
                } else {
                        /* Mandatory signing or bad packet after signing started - fail and disconnect. */
                        if (seq)
                                DEBUG(0, ("signing_good: BAD SIG: seq %u\n", (unsigned int)seq));
                        return False;
                }
        }
        return True;
}       

/***********************************************************
 SMB signing - Simple implementation - calculate a MAC on the packet
************************************************************/

static void simple_packet_signature(struct smb_basic_signing_context *data, 
                                    const uchar *buf, uint32 seq_number, 
                                    unsigned char calc_md5_mac[16])
{
        const size_t offset_end_of_sig = (smb_ss_field + 8);
        unsigned char sequence_buf[8];
        struct MD5Context md5_ctx;
#if 0
        /* JRA - apparently this is incorrect. */
        unsigned char key_buf[16];
#endif

        /*
         * Firstly put the sequence number into the first 4 bytes.
         * and zero out the next 4 bytes.
         *
         * We do this here, to avoid modifying the packet.
         */

        DEBUG(10,("simple_packet_signature: sequence number %u\n", seq_number ));

        SIVAL(sequence_buf, 0, seq_number);
        SIVAL(sequence_buf, 4, 0);

        /* Calculate the 16 byte MAC - but don't alter the data in the
           incoming packet.
           
           This makes for a bit of fussing about, but it's not too bad.
        */
        MD5Init(&md5_ctx);

        /* intialise with the key */
        MD5Update(&md5_ctx, data->mac_key.data, data->mac_key.length); 
#if 0
        /* JRA - apparently this is incorrect. */
        /* NB. When making and verifying SMB signatures, Windows apparently
                zero-pads the key to 128 bits if it isn't long enough.
                From Nalin Dahyabhai <nalin@redhat.com> */
        if (data->mac_key.length < sizeof(key_buf)) {
                memset(key_buf, 0, sizeof(key_buf));
                MD5Update(&md5_ctx, key_buf, sizeof(key_buf) - data->mac_key.length);
        }
#endif

        /* copy in the first bit of the SMB header */
        MD5Update(&md5_ctx, buf + 4, smb_ss_field - 4);

        /* copy in the sequence number, instead of the signature */
        MD5Update(&md5_ctx, sequence_buf, sizeof(sequence_buf));

        /* copy in the rest of the packet in, skipping the signature */
        MD5Update(&md5_ctx, buf + offset_end_of_sig, 
                  smb_len(buf) - (offset_end_of_sig - 4));

        /* calculate the MD5 sig */ 
        MD5Final(calc_md5_mac, &md5_ctx);
}


/***********************************************************
 SMB signing - Client implementation - send the MAC.
************************************************************/

static void client_sign_outgoing_message(char *outbuf, struct smb_sign_info *si)
{
        unsigned char calc_md5_mac[16];
        struct smb_basic_signing_context *data =
                (struct smb_basic_signing_context *)si->signing_context;

        if (!si->doing_signing)
                return;

        /* JRA Paranioa test - we should be able to get rid of this... */
        if (smb_len(outbuf) < (smb_ss_field + 8 - 4)) {
                DEBUG(1, ("client_sign_outgoing_message: Logic error. Can't check signature on short packet! smb_len = %u\n",
                                        smb_len(outbuf) ));
                abort();
        }

        /* mark the packet as signed - BEFORE we sign it...*/
        mark_packet_signed(outbuf);

        simple_packet_signature(data, (const unsigned char *)outbuf,
                                data->send_seq_num, calc_md5_mac);

        DEBUG(10, ("client_sign_outgoing_message: sent SMB signature of\n"));
        dump_data(10, (const char *)calc_md5_mac, 8);

        memcpy(&outbuf[smb_ss_field], calc_md5_mac, 8);

/*      cli->outbuf[smb_ss_field+2]=0; 
        Uncomment this to test if the remote server actually verifies signatures...*/

        /* Instead of re-introducing the trans_info_conect we
           used to have here, we use the fact that during a
           SMBtrans/SMBtrans2/SMBnttrans send that the mid stays
           constant. This means that calling store_sequence_for_reply()
           will return False for all trans secondaries, as the mid is already
           on the stored sequence list. As the send_seqence_number must
           remain constant for all primary+secondary trans sends, we
           only increment the send sequence number when we successfully
           add a new entry to the outstanding sequence list. This means
           I can isolate the fix here rather than re-adding the trans
           signing on/off calls in libsmb/clitrans2.c JRA.
         */
        
        if (store_sequence_for_reply(&data->outstanding_packet_list, SVAL(outbuf,smb_mid), data->send_seq_num + 1)) {
                data->send_seq_num += 2;
        }
}

/***********************************************************
 SMB signing - Client implementation - check a MAC sent by server.
************************************************************/

static BOOL client_check_incoming_message(char *inbuf, struct smb_sign_info *si, BOOL must_be_ok)
{
        BOOL good;
        uint32 reply_seq_number;
        unsigned char calc_md5_mac[16];
        unsigned char *server_sent_mac;

        struct smb_basic_signing_context *data =
                (struct smb_basic_signing_context *)si->signing_context;

        if (!si->doing_signing)
                return True;

        if (smb_len(inbuf) < (smb_ss_field + 8 - 4)) {
                DEBUG(1, ("client_check_incoming_message: Can't check signature on short packet! smb_len = %u\n", smb_len(inbuf)));
                return False;
        }

        if (!get_sequence_for_reply(&data->outstanding_packet_list, SVAL(inbuf, smb_mid), &reply_seq_number)) {
                DEBUG(1, ("client_check_incoming_message: received message "
                        "with mid %u with no matching send record.\n", (unsigned int)SVAL(inbuf, smb_mid) ));
                return False;
        }

        simple_packet_signature(data, (const unsigned char *)inbuf,
                                reply_seq_number, calc_md5_mac);

        server_sent_mac = (unsigned char *)&inbuf[smb_ss_field];
        good = (memcmp(server_sent_mac, calc_md5_mac, 8) == 0);
        
        if (!good) {
                DEBUG(5, ("client_check_incoming_message: BAD SIG: wanted SMB signature of\n"));
                dump_data(5, (const char *)calc_md5_mac, 8);
                
                DEBUG(5, ("client_check_incoming_message: BAD SIG: got SMB signature of\n"));
                dump_data(5, (const char *)server_sent_mac, 8);
#if 1 /* JRATEST */
                {
                        int i;
                        for (i = -5; i < 5; i++) {
                                simple_packet_signature(data, (const unsigned char *)inbuf, reply_seq_number+i, calc_md5_mac);
                                if (memcmp(server_sent_mac, calc_md5_mac, 8) == 0) {
                                        DEBUG(0,("client_check_incoming_message: out of seq. seq num %u matches. \
We were expecting seq %u\n", reply_seq_number+i, reply_seq_number ));
                                        break;
                                }
                        }
                }
#endif /* JRATEST */

        } else {
                DEBUG(10, ("client_check_incoming_message: seq %u: got good SMB signature of\n", (unsigned int)reply_seq_number));
                dump_data(10, (const char *)server_sent_mac, 8);
        }
        return signing_good(inbuf, si, good, reply_seq_number, must_be_ok);
}

/***********************************************************
 SMB signing - Simple implementation - free signing context
************************************************************/

static void simple_free_signing_context(struct smb_sign_info *si)
{
        struct smb_basic_signing_context *data =
                (struct smb_basic_signing_context *)si->signing_context;
        struct outstanding_packet_lookup *list;
        struct outstanding_packet_lookup *next;
        
        for (list = data->outstanding_packet_list; list; list = next) {
                next = list->next;
                DLIST_REMOVE(data->outstanding_packet_list, list);
                SAFE_FREE(list);
        }

        data_blob_free(&data->mac_key);

        SAFE_FREE(si->signing_context);

        return;
}

/***********************************************************
 SMB signing - Simple implementation - setup the MAC key.
************************************************************/

BOOL cli_simple_set_signing(struct cli_state *cli,
                            const DATA_BLOB user_session_key,
                            const DATA_BLOB response)
{
        struct smb_basic_signing_context *data;

        if (!user_session_key.length)
                return False;

        if (!cli_set_smb_signing_common(cli)) {
                return False;
        }

        if (!set_smb_signing_real_common(&cli->sign_info)) {
                return False;
        }

        data = SMB_XMALLOC_P(struct smb_basic_signing_context);
        memset(data, '\0', sizeof(*data));

        cli->sign_info.signing_context = data;
        
        data->mac_key = data_blob(NULL, response.length + user_session_key.length);

        memcpy(&data->mac_key.data[0], user_session_key.data, user_session_key.length);

        DEBUG(10, ("cli_simple_set_signing: user_session_key\n"));
        dump_data(10, (const char *)user_session_key.data, user_session_key.length);

        if (response.length) {
                memcpy(&data->mac_key.data[user_session_key.length],response.data, response.length);
                DEBUG(10, ("cli_simple_set_signing: response_data\n"));
                dump_data(10, (const char *)response.data, response.length);
        } else {
                DEBUG(10, ("cli_simple_set_signing: NULL response_data\n"));
        }

        dump_data_pw("MAC ssession key is:\n", data->mac_key.data, data->mac_key.length);

        /* Initialise the sequence number */
        data->send_seq_num = 0;

        /* Initialise the list of outstanding packets */
        data->outstanding_packet_list = NULL;

        cli->sign_info.sign_outgoing_message = client_sign_outgoing_message;
        cli->sign_info.check_incoming_message = client_check_incoming_message;
        cli->sign_info.free_signing_context = simple_free_signing_context;

        return True;
}

/***********************************************************
 SMB signing - TEMP implementation - calculate a MAC to send.
************************************************************/

static void temp_sign_outgoing_message(char *outbuf, struct smb_sign_info *si)
{
        /* mark the packet as signed - BEFORE we sign it...*/
        mark_packet_signed(outbuf);

        /* I wonder what BSRSPYL stands for - but this is what MS 
           actually sends! */
        memcpy(&outbuf[smb_ss_field], "BSRSPYL ", 8);
        return;
}

/***********************************************************
 SMB signing - TEMP implementation - check a MAC sent by server.
************************************************************/

static BOOL temp_check_incoming_message(char *inbuf, struct smb_sign_info *si, BOOL foo)
{
        return True;
}

/***********************************************************
 SMB signing - TEMP implementation - free signing context
************************************************************/

static void temp_free_signing_context(struct smb_sign_info *si)
{
        return;
}

/***********************************************************
 SMB signing - NULL implementation - setup the MAC key.
************************************************************/

BOOL cli_null_set_signing(struct cli_state *cli)
{
        return null_set_signing(&cli->sign_info);
}

/***********************************************************
 SMB signing - temp implementation - setup the MAC key.
************************************************************/

BOOL cli_temp_set_signing(struct cli_state *cli)
{
        if (!cli_set_smb_signing_common(cli)) {
                return False;
        }

        cli->sign_info.signing_context = NULL;
        
        cli->sign_info.sign_outgoing_message = temp_sign_outgoing_message;
        cli->sign_info.check_incoming_message = temp_check_incoming_message;
        cli->sign_info.free_signing_context = temp_free_signing_context;

        return True;
}

void cli_free_signing_context(struct cli_state *cli)
{
        free_signing_context(&cli->sign_info);
}

/**
 * Sign a packet with the current mechanism
 */
 
void cli_calculate_sign_mac(struct cli_state *cli)
{
        cli->sign_info.sign_outgoing_message(cli->outbuf, &cli->sign_info);
}

/**
 * Check a packet with the current mechanism
 * @return False if we had an established signing connection
 *         which had a bad checksum, True otherwise.
 */
 
BOOL cli_check_sign_mac(struct cli_state *cli) 
{
        if (!cli->sign_info.check_incoming_message(cli->inbuf, &cli->sign_info, True)) {
                free_signing_context(&cli->sign_info);  
                return False;
        }
        return True;
}

/***********************************************************
 Enter trans/trans2/nttrans state.
************************************************************/

BOOL client_set_trans_sign_state_on(struct cli_state *cli, uint16 mid)
{
        struct smb_sign_info *si = &cli->sign_info;
        struct smb_basic_signing_context *data = (struct smb_basic_signing_context *)si->signing_context;

        if (!si->doing_signing) {
                return True;
        }

        if (!data) {
                return False;
        }

        if (!set_sequence_can_delete_flag(&data->outstanding_packet_list, mid, False)) {
                return False;
        }

        return True;
}

/***********************************************************
 Leave trans/trans2/nttrans state.
************************************************************/

BOOL client_set_trans_sign_state_off(struct cli_state *cli, uint16 mid)
{
        uint32 reply_seq_num;
        struct smb_sign_info *si = &cli->sign_info;
        struct smb_basic_signing_context *data = (struct smb_basic_signing_context *)si->signing_context;

        if (!si->doing_signing) {
                return True;
        }

        if (!data) {
                return False;
        }

        if (!set_sequence_can_delete_flag(&data->outstanding_packet_list, mid, True)) {
                return False;
        }

        /* Now delete the stored mid entry. */
        if (!get_sequence_for_reply(&data->outstanding_packet_list, mid, &reply_seq_num)) {
                return False;
        }

        return True;
}

/***********************************************************
 SMB signing - Server implementation - send the MAC.
************************************************************/

static void srv_sign_outgoing_message(char *outbuf, struct smb_sign_info *si)
{
        unsigned char calc_md5_mac[16];
        struct smb_basic_signing_context *data =
                (struct smb_basic_signing_context *)si->signing_context;
        uint32 send_seq_number = data->send_seq_num-1;
        uint16 mid;

        if (!si->doing_signing) {
                return;
        }

        /* JRA Paranioa test - we should be able to get rid of this... */
        if (smb_len(outbuf) < (smb_ss_field + 8 - 4)) {
                DEBUG(1, ("srv_sign_outgoing_message: Logic error. Can't send signature on short packet! smb_len = %u\n",
                                        smb_len(outbuf) ));
                abort();
        }

        /* mark the packet as signed - BEFORE we sign it...*/
        mark_packet_signed(outbuf);

        mid = SVAL(outbuf, smb_mid);

        /* See if this is a reply for a deferred packet. */
        get_sequence_for_reply(&data->outstanding_packet_list, mid, &send_seq_number);

        simple_packet_signature(data, (const unsigned char *)outbuf, send_seq_number, calc_md5_mac);

        DEBUG(10, ("srv_sign_outgoing_message: seq %u: sent SMB signature of\n", (unsigned int)send_seq_number));
        dump_data(10, (const char *)calc_md5_mac, 8);

        memcpy(&outbuf[smb_ss_field], calc_md5_mac, 8);

/*      cli->outbuf[smb_ss_field+2]=0; 
        Uncomment this to test if the remote client actually verifies signatures...*/
}

/***********************************************************
 SMB signing - Server implementation - check a MAC sent by server.
************************************************************/

static BOOL srv_check_incoming_message(char *inbuf, struct smb_sign_info *si, BOOL must_be_ok)
{
        BOOL good;
        struct smb_basic_signing_context *data =
                (struct smb_basic_signing_context *)si->signing_context;
        uint32 reply_seq_number = data->send_seq_num;
        uint32 saved_seq;
        unsigned char calc_md5_mac[16];
        unsigned char *server_sent_mac;

        if (!si->doing_signing)
                return True;

        if (smb_len(inbuf) < (smb_ss_field + 8 - 4)) {
                DEBUG(1, ("srv_check_incoming_message: Can't check signature on short packet! smb_len = %u\n", smb_len(inbuf)));
                return False;
        }

        /* We always increment the sequence number. */
        data->send_seq_num += 2;

        saved_seq = reply_seq_number;
        simple_packet_signature(data, (const unsigned char *)inbuf, reply_seq_number, calc_md5_mac);

        server_sent_mac = (unsigned char *)&inbuf[smb_ss_field];
        good = (memcmp(server_sent_mac, calc_md5_mac, 8) == 0);
        
        if (!good) {

                if (saved_seq) {
                        DEBUG(0, ("srv_check_incoming_message: BAD SIG: seq %u wanted SMB signature of\n",
                                        (unsigned int)saved_seq));
                        dump_data(5, (const char *)calc_md5_mac, 8);

                        DEBUG(0, ("srv_check_incoming_message: BAD SIG: seq %u got SMB signature of\n",
                                                (unsigned int)reply_seq_number));
                        dump_data(5, (const char *)server_sent_mac, 8);
                }
                
#if 1 /* JRATEST */
                {
                        int i;
                        reply_seq_number -= 5;
                        for (i = 0; i < 10; i++, reply_seq_number++) {
                                simple_packet_signature(data, (const unsigned char *)inbuf, reply_seq_number, calc_md5_mac);
                                if (memcmp(server_sent_mac, calc_md5_mac, 8) == 0) {
                                        DEBUG(0,("srv_check_incoming_message: out of seq. seq num %u matches. \
We were expecting seq %u\n", reply_seq_number, saved_seq ));
                                        break;
                                }
                        }
                }
#endif /* JRATEST */

        } else {
                DEBUG(10, ("srv_check_incoming_message: seq %u: (current is %u) got good SMB signature of\n", (unsigned int)reply_seq_number, (unsigned int)data->send_seq_num));
                dump_data(10, (const char *)server_sent_mac, 8);
        }

        return (signing_good(inbuf, si, good, saved_seq, must_be_ok));
}

/***********************************************************
 SMB signing - server API's.
************************************************************/

static struct smb_sign_info srv_sign_info = {
        null_sign_outgoing_message,
        null_check_incoming_message,
        null_free_signing_context,
        NULL,
        False,
        False,
        False,
        False
};

/***********************************************************
 Turn signing off or on for oplock break code.
************************************************************/

BOOL srv_oplock_set_signing(BOOL onoff)
{
        BOOL ret = srv_sign_info.doing_signing;
        srv_sign_info.doing_signing = onoff;
        return ret;
}

/***********************************************************
 Called to validate an incoming packet from the client.
************************************************************/

BOOL srv_check_sign_mac(char *inbuf, BOOL must_be_ok)
{
        /* Check if it's a session keepalive. */
        if(CVAL(inbuf,0) == SMBkeepalive)
                return True;

        return srv_sign_info.check_incoming_message(inbuf, &srv_sign_info, must_be_ok);
}

/***********************************************************
 Called to sign an outgoing packet to the client.
************************************************************/

void srv_calculate_sign_mac(char *outbuf)
{
        /* Check if it's a session keepalive. */
        /* JRA Paranioa test - do we ever generate these in the server ? */
        if(CVAL(outbuf,0) == SMBkeepalive)
                return;

        srv_sign_info.sign_outgoing_message(outbuf, &srv_sign_info);
}

/***********************************************************
 Called by server to defer an outgoing packet.
************************************************************/

void srv_defer_sign_response(uint16 mid)
{
        struct smb_basic_signing_context *data;

        if (!srv_sign_info.doing_signing)
                return;

        data = (struct smb_basic_signing_context *)srv_sign_info.signing_context;

        if (!data)
                return;

        /*
         * Ensure we only store this mid reply once...
         */

        store_sequence_for_reply(&data->outstanding_packet_list, mid,
                                 data->send_seq_num-1);
}

/***********************************************************
 Called to remove sequence records when a deferred packet is
 cancelled by mid. This should never find one....
************************************************************/

void srv_cancel_sign_response(uint16 mid)
{
        struct smb_basic_signing_context *data;
        uint32 dummy_seq;

        if (!srv_sign_info.doing_signing)
                return;

        data = (struct smb_basic_signing_context *)srv_sign_info.signing_context;

        if (!data)
                return;

        DEBUG(10,("srv_cancel_sign_response: for mid %u\n", (unsigned int)mid ));

        while (get_sequence_for_reply(&data->outstanding_packet_list, mid, &dummy_seq))
                ;

        /* cancel doesn't send a reply so doesn't burn a sequence number. */
        data->send_seq_num -= 1;
}

/***********************************************************
 Called by server negprot when signing has been negotiated.
************************************************************/

void srv_set_signing_negotiated(void)
{
        srv_sign_info.allow_smb_signing = True;
        srv_sign_info.negotiated_smb_signing = True;
        if (lp_server_signing() == Required)
                srv_sign_info.mandatory_signing = True;

        srv_sign_info.sign_outgoing_message = temp_sign_outgoing_message;
        srv_sign_info.check_incoming_message = temp_check_incoming_message;
        srv_sign_info.free_signing_context = temp_free_signing_context;
}

/***********************************************************
 Returns whether signing is active. We can't use sendfile or raw
 reads/writes if it is.
************************************************************/

BOOL srv_is_signing_active(void)
{
        return srv_sign_info.doing_signing;
}


/***********************************************************
 Returns whether signing is negotiated. We can't use it unless it was
 in the negprot.  
************************************************************/

BOOL srv_is_signing_negotiated(void)
{
        return srv_sign_info.negotiated_smb_signing;
}

/***********************************************************
 Returns whether signing is actually happening
************************************************************/

BOOL srv_signing_started(void)
{
        struct smb_basic_signing_context *data;

        if (!srv_sign_info.doing_signing) {
                return False;
        }

        data = (struct smb_basic_signing_context *)srv_sign_info.signing_context;
        if (!data)
                return False;

        if (data->send_seq_num == 0) {
                return False;
        }

        return True;
}

/***********************************************************
 Turn on signing from this packet onwards. 
************************************************************/

void srv_set_signing(const DATA_BLOB user_session_key, const DATA_BLOB response)
{
        struct smb_basic_signing_context *data;

        if (!user_session_key.length)
                return;

        if (!srv_sign_info.negotiated_smb_signing && !srv_sign_info.mandatory_signing) {
                DEBUG(5,("srv_set_signing: signing negotiated = %u, mandatory_signing = %u. Not allowing smb signing.\n",
                        (unsigned int)srv_sign_info.negotiated_smb_signing,
                        (unsigned int)srv_sign_info.mandatory_signing ));
                return;
        }

        /* Once we've turned on, ignore any more sessionsetups. */
        if (srv_sign_info.doing_signing) {
                return;
        }
        
        if (srv_sign_info.free_signing_context)
                srv_sign_info.free_signing_context(&srv_sign_info);
        
        srv_sign_info.doing_signing = True;

        data = SMB_XMALLOC_P(struct smb_basic_signing_context);
        memset(data, '\0', sizeof(*data));

        srv_sign_info.signing_context = data;
        
        data->mac_key = data_blob(NULL, response.length + user_session_key.length);

        memcpy(&data->mac_key.data[0], user_session_key.data, user_session_key.length);
        if (response.length)
                memcpy(&data->mac_key.data[user_session_key.length],response.data, response.length);

        dump_data_pw("MAC ssession key is:\n", data->mac_key.data, data->mac_key.length);

        DEBUG(3,("srv_set_signing: turning on SMB signing: signing negotiated = %s, mandatory_signing = %s.\n",
                                BOOLSTR(srv_sign_info.negotiated_smb_signing),
                                BOOLSTR(srv_sign_info.mandatory_signing) ));

        /* Initialise the sequence number */
        data->send_seq_num = 0;

        /* Initialise the list of outstanding packets */
        data->outstanding_packet_list = NULL;

        srv_sign_info.sign_outgoing_message = srv_sign_outgoing_message;
        srv_sign_info.check_incoming_message = srv_check_incoming_message;
        srv_sign_info.free_signing_context = simple_free_signing_context;
}

---