source3/libsmb/smb_signing.c

   1 /*
   2    Unix SMB/CIFS implementation.
   3    SMB Signing Code
   4    Copyright (C) Jeremy Allison 2003.
   5    Copyright (C) Andrew Bartlett <abartlet@samba.org> 2002-2003
   6    Copyright (C) Stefan Metzmacher 2009
   7
   8    This program is free software; you can redistribute it and/or modify
   9    it under the terms of the GNU General Public License as published by
  10    the Free Software Foundation; either version 3 of the License, or
  11    (at your option) any later version.
  12
  13    This program is distributed in the hope that it will be useful,
  14    but WITHOUT ANY WARRANTY; without even the implied warranty of
  15    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16    GNU General Public License for more details.
  17
  18    You should have received a copy of the GNU General Public License
  19    along with this program.  If not, see <http://www.gnu.org/licenses/>.
  20 */
  21
  22 #include "includes.h"
  23 #include "../lib/crypto/md5.h"
  24 #include "smb_signing.h"
  25
  26 /* Used by the SMB signing functions. */
  27
  28 struct smb_signing_state {
  29         /* is signing localy allowed */
  30         bool allowed;
  31
  32         /* is signing localy mandatory */
  33         bool mandatory;
  34
  35         /* is signing negotiated by the peer */
  36         bool negotiated;
  37
  38         /* send BSRSPYL signatures */
  39         bool bsrspyl;
  40
  41         bool active; /* Have I ever seen a validly signed packet? */
  42
  43         /* mac_key.length > 0 means signing is started */
  44         DATA_BLOB mac_key;
  45
  46         /* the next expected seqnum */
  47         uint32_t seqnum;
  48
  49         TALLOC_CTX *mem_ctx;
  50         void *(*alloc_fn)(TALLOC_CTX *mem_ctx, size_t len);
  51         void (*free_fn)(TALLOC_CTX *mem_ctx, void *ptr);
  52 };
  53
  54 static void smb_signing_reset_info(struct smb_signing_state *si)
  55 {
  56         si->active = false;
  57         si->bsrspyl = false;
  58         si->seqnum = 0;
  59
  60         if (si->free_fn) {
  61                 si->free_fn(si->mem_ctx, si->mac_key.data);
  62         } else {
  63                 talloc_free(si->mac_key.data);
  64         }
  65         si->mac_key.data = NULL;
  66         si->mac_key.length = 0;
  67 }
  68
  69 struct smb_signing_state *smb_signing_init_ex(TALLOC_CTX *mem_ctx,
  70                                               bool allowed,
  71                                               bool mandatory,
  72                                               void *(*alloc_fn)(TALLOC_CTX *, size_t),
  73                                               void (*free_fn)(TALLOC_CTX *, void *))
  74 {
  75         struct smb_signing_state *si;
  76
  77         if (alloc_fn) {
  78                 void *p = alloc_fn(mem_ctx, sizeof(struct smb_signing_state));
  79                 if (p == NULL) {
  80                         return NULL;
  81                 }
  82                 memset(p, 0, sizeof(struct smb_signing_state));
  83                 si = (struct smb_signing_state *)p;
  84                 si->mem_ctx = mem_ctx;
  85                 si->alloc_fn = alloc_fn;
  86                 si->free_fn = free_fn;
  87         } else {
  88                 si = talloc_zero(mem_ctx, struct smb_signing_state);
  89                 if (si == NULL) {
  90                         return NULL;
  91                 }
  92         }
  93
  94         if (mandatory) {
  95                 allowed = true;
  96         }
  97
  98         si->allowed = allowed;
  99         si->mandatory = mandatory;
 100
 101         return si;
 102 }
 103
 104 struct smb_signing_state *smb_signing_init(TALLOC_CTX *mem_ctx,
 105                                            bool allowed,
 106                                            bool mandatory)
 107 {
 108         return smb_signing_init_ex(mem_ctx, allowed, mandatory, NULL, NULL);
 109 }
 110
 111 static bool smb_signing_good(struct smb_signing_state *si,
 112                              bool good, uint32_t seq)
 113 {
 114         if (good) {
 115                 if (!si->active) {
 116                         si->active = true;
 117                 }
 118                 return true;
 119         }
 120
 121         if (!si->mandatory && !si->active) {
 122                 /* Non-mandatory signing - just turn off if this is the first bad packet.. */
 123                 DEBUG(5, ("smb_signing_good: signing negotiated but not required and peer\n"
 124                           "isn't sending correct signatures. Turning off.\n"));
 125                 smb_signing_reset_info(si);
 126                 return true;
 127         }
 128
 129         /* Mandatory signing or bad packet after signing started - fail and disconnect. */
 130         DEBUG(0, ("smb_signing_good: BAD SIG: seq %u\n", (unsigned int)seq));
 131         return false;
 132 }
 133
 134 static void smb_signing_md5(const DATA_BLOB *mac_key,
 135                             const uint8_t *buf, uint32_t seq_number,
 136                             uint8_t calc_md5_mac[16])
 137 {
 138         const size_t offset_end_of_sig = (smb_ss_field + 8);
 139         uint8_t sequence_buf[8];
 140         struct MD5Context md5_ctx;
 141
 142         /*
 143          * Firstly put the sequence number into the first 4 bytes.
 144          * and zero out the next 4 bytes.
 145          *
 146          * We do this here, to avoid modifying the packet.
 147          */
 148
 149         DEBUG(10,("smb_signing_md5: sequence number %u\n", seq_number ));
 150
 151         SIVAL(sequence_buf, 0, seq_number);
 152         SIVAL(sequence_buf, 4, 0);
 153
 154         /* Calculate the 16 byte MAC - but don't alter the data in the
 155            incoming packet.
 156
 157            This makes for a bit of fussing about, but it's not too bad.
 158         */
 159         MD5Init(&md5_ctx);
 160
 161         /* intialise with the key */
 162         MD5Update(&md5_ctx, mac_key->data, mac_key->length);
 163
 164         /* copy in the first bit of the SMB header */
 165         MD5Update(&md5_ctx, buf + 4, smb_ss_field - 4);
 166
 167         /* copy in the sequence number, instead of the signature */
 168         MD5Update(&md5_ctx, sequence_buf, sizeof(sequence_buf));
 169
 170         /* copy in the rest of the packet in, skipping the signature */
 171         MD5Update(&md5_ctx, buf + offset_end_of_sig,
 172                   smb_len(buf) - (offset_end_of_sig - 4));
 173
 174         /* calculate the MD5 sig */
 175         MD5Final(calc_md5_mac, &md5_ctx);
 176 }
 177
 178 uint32_t smb_signing_next_seqnum(struct smb_signing_state *si, bool oneway)
 179 {
 180         uint32_t seqnum;
 181
 182         if (si->mac_key.length == 0) {
 183                 return 0;
 184         }
 185
 186         seqnum = si->seqnum;
 187         if (oneway) {
 188                 si->seqnum += 1;
 189         } else {
 190                 si->seqnum += 2;
 191         }
 192
 193         return seqnum;
 194 }
 195
 196 void smb_signing_cancel_reply(struct smb_signing_state *si, bool oneway)
 197 {
 198         if (si->mac_key.length == 0) {
 199                 return;
 200         }
 201
 202         if (oneway) {
 203                 si->seqnum -= 1;
 204         } else {
 205                 si->seqnum -= 2;
 206         }
 207 }
 208
 209 void smb_signing_sign_pdu(struct smb_signing_state *si,
 210                           uint8_t *outbuf, uint32_t seqnum)
 211 {
 212         uint8_t calc_md5_mac[16];
 213         uint16_t flags2;
 214
 215         if (si->mac_key.length == 0) {
 216                 if (!si->bsrspyl) {
 217                         return;
 218                 }
 219         }
 220
 221         /* JRA Paranioa test - we should be able to get rid of this... */
 222         if (smb_len(outbuf) < (smb_ss_field + 8 - 4)) {
 223                 DEBUG(1,("smb_signing_sign_pdu: Logic error. "
 224                          "Can't check signature on short packet! smb_len = %u\n",
 225                          smb_len(outbuf)));
 226                 abort();
 227         }
 228
 229         /* mark the packet as signed - BEFORE we sign it...*/
 230         flags2 = SVAL(outbuf,smb_flg2);
 231         flags2 |= FLAGS2_SMB_SECURITY_SIGNATURES;
 232         SSVAL(outbuf, smb_flg2, flags2);
 233
 234         if (si->bsrspyl) {
 235                 /* I wonder what BSRSPYL stands for - but this is what MS
 236                    actually sends! */
 237                 memcpy(calc_md5_mac, "BSRSPYL ", 8);
 238         } else {
 239                 smb_signing_md5(&si->mac_key, outbuf,
 240                                 seqnum, calc_md5_mac);
 241         }
 242
 243         DEBUG(10, ("smb_signing_sign_pdu: sent SMB signature of\n"));
 244         dump_data(10, calc_md5_mac, 8);
 245
 246         memcpy(&outbuf[smb_ss_field], calc_md5_mac, 8);
 247
 248 /*      outbuf[smb_ss_field+2]=0;
 249         Uncomment this to test if the remote server actually verifies signatures...*/
 250 }
 251
 252 bool smb_signing_check_pdu(struct smb_signing_state *si,
 253                            const uint8_t *inbuf, uint32_t seqnum)
 254 {
 255         bool good;
 256         uint8_t calc_md5_mac[16];
 257         const uint8_t *reply_sent_mac;
 258
 259         if (si->mac_key.length == 0) {
 260                 return true;
 261         }
 262
 263         if (smb_len(inbuf) < (smb_ss_field + 8 - 4)) {
 264                 DEBUG(1,("smb_signing_check_pdu: Can't check signature "
 265                          "on short packet! smb_len = %u\n",
 266                          smb_len(inbuf)));
 267                 return False;
 268         }
 269
 270         smb_signing_md5(&si->mac_key, inbuf,
 271                         seqnum, calc_md5_mac);
 272
 273         reply_sent_mac = &inbuf[smb_ss_field];
 274         good = (memcmp(reply_sent_mac, calc_md5_mac, 8) == 0);
 275
 276         if (!good) {
 277                 int i;
 278                 const int sign_range = 5;
 279
 280                 DEBUG(5, ("smb_signing_check_pdu: BAD SIG: wanted SMB signature of\n"));
 281                 dump_data(5, calc_md5_mac, 8);
 282
 283                 DEBUG(5, ("smb_signing_check_pdu: BAD SIG: got SMB signature of\n"));
 284                 dump_data(5, reply_sent_mac, 8);
 285
 286                 for (i = -sign_range; i < sign_range; i++) {
 287                         smb_signing_md5(&si->mac_key, inbuf,
 288                                         seqnum+i, calc_md5_mac);
 289                         if (memcmp(reply_sent_mac, calc_md5_mac, 8) == 0) {
 290                                 DEBUG(0,("smb_signing_check_pdu: "
 291                                          "out of seq. seq num %u matches. "
 292                                          "We were expecting seq %u\n",
 293                                          (unsigned int)seqnum+i,
 294                                          (unsigned int)seqnum));
 295                                 break;
 296                         }
 297                 }
 298         } else {
 299                 DEBUG(10, ("smb_signing_check_pdu: seq %u: "
 300                            "got good SMB signature of\n",
 301                            (unsigned int)seqnum));
 302                 dump_data(10, reply_sent_mac, 8);
 303         }
 304
 305         return smb_signing_good(si, good, seqnum);
 306 }
 307
 308 bool smb_signing_set_bsrspyl(struct smb_signing_state *si)
 309 {
 310         if (!si->negotiated) {
 311                 return false;
 312         }
 313
 314         if (si->active) {
 315                 return false;
 316         }
 317
 318         si->bsrspyl = true;
 319
 320         return true;
 321 }
 322
 323 bool smb_signing_activate(struct smb_signing_state *si,
 324                           const DATA_BLOB user_session_key,
 325                           const DATA_BLOB response)
 326 {
 327         size_t len;
 328         off_t ofs;
 329
 330         if (!user_session_key.length) {
 331                 return false;
 332         }
 333
 334         if (!si->negotiated) {
 335                 return false;
 336         }
 337
 338         if (si->active) {
 339                 return false;
 340         }
 341
 342         if (si->mac_key.length > 0) {
 343                 return false;
 344         }
 345
 346         smb_signing_reset_info(si);
 347
 348         len = response.length + user_session_key.length;
 349         if (si->alloc_fn) {
 350                 si->mac_key.data = (uint8_t *)si->alloc_fn(si->mem_ctx, len);
 351                 if (si->mac_key.data == NULL) {
 352                         return false;
 353                 }
 354         } else {
 355                 si->mac_key.data = (uint8_t *)talloc_size(si, len);
 356                 if (si->mac_key.data == NULL) {
 357                         return false;
 358                 }
 359         }
 360         si->mac_key.length = len;
 361
 362         ofs = 0;
 363         memcpy(&si->mac_key.data[ofs], user_session_key.data, user_session_key.length);
 364
 365         DEBUG(10, ("smb_signing_activate: user_session_key\n"));
 366         dump_data(10, user_session_key.data, user_session_key.length);
 367
 368         if (response.length) {
 369                 ofs = user_session_key.length;
 370                 memcpy(&si->mac_key.data[ofs], response.data, response.length);
 371                 DEBUG(10, ("smb_signing_activate: response_data\n"));
 372                 dump_data(10, response.data, response.length);
 373         } else {
 374                 DEBUG(10, ("smb_signing_activate: NULL response_data\n"));
 375         }
 376
 377         dump_data_pw("smb_signing_activate: mac key is:\n",
 378                      si->mac_key.data, si->mac_key.length);
 379
 380         /* Initialise the sequence number */
 381         si->seqnum = 2;
 382
 383         return true;
 384 }
 385
 386 bool smb_signing_is_active(struct smb_signing_state *si)
 387 {
 388         return si->active;
 389 }
 390
 391 bool smb_signing_is_allowed(struct smb_signing_state *si)
 392 {
 393         return si->allowed;
 394 }
 395
 396 bool smb_signing_is_mandatory(struct smb_signing_state *si)
 397 {
 398         return si->mandatory;
 399 }
 400
 401 bool smb_signing_set_negotiated(struct smb_signing_state *si)
 402 {
 403         if (!si->allowed) {
 404                 return false;
 405         }
 406
 407         si->negotiated = true;
 408
 409         return true;
 410 }
 411
 412 bool smb_signing_is_negotiated(struct smb_signing_state *si)
 413 {
 414         return si->negotiated;
 415 }