Created
August 20, 2015 16:27
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A FAT32 fragmenter, because I am a horrible person.
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#!/usr/bin/env python | |
import random | |
import struct | |
import sys | |
# Most of the Fat32 class was cribbed from https://gist.github.com/jonte/4577833 | |
def ppNum(num): | |
return "%s (%s)" % (hex(num), num) | |
class Fat32: | |
def __init__(self, filename): | |
self.fs = open(filename, 'r+b') | |
def getRawBytes(self, pos, numBytes): | |
self.fs.seek(pos) | |
return self.fs.read(numBytes) | |
def putRawBytes(self, pos, data): | |
self.fs.seek(pos) | |
self.fs.write(data) | |
def putUInt32(self, pos, n): | |
print 'write %10s@%08x' % (n, pos) | |
self.fs.seek(pos) | |
self.putRawBytes(pos, struct.pack('<i', n)) | |
def putUInt16(self, pos, n): | |
self.fs.seek(pos) | |
self.putRawBytes(pos, struct.pack('<H', n)) | |
def putUInt8(self, pos, n): | |
self.fs.seek(pos) | |
self.putRawBytes(pos, struct.pack('<B', n)) | |
def getBytes(self, pos, numBytes): | |
byte = self.getRawBytes(pos, numBytes) | |
if (numBytes == 2): | |
formatString = "H" | |
elif (numBytes == 1): | |
formatString = "B" | |
elif (numBytes == 4): | |
formatString = "i" | |
else: | |
raise Exception("Not implemented") | |
return struct.unpack("<"+formatString, byte)[0] | |
def getString(self, pos, numBytes): | |
raw = self.getRawBytes(pos, numBytes) | |
return struct.unpack(str(numBytes)+"s", raw)[0] | |
@property | |
def bytesPerSector(self): | |
return self.getBytes(11,2) | |
@property | |
def sectorsPerCluster(self): | |
return self.getBytes(13,1) | |
@property | |
def bytesPerCluster(self): | |
return self.bytesPerSector * self.sectorsPerCluster | |
@property | |
def reservedSectorCount(self): | |
return self.getBytes(14,2) | |
@property | |
def numberOfFATs(self): | |
return self.getBytes(16,1) | |
def FATStart(self, numFat): | |
return self.reservedSectorCount * self.bytesPerSector + (self.FATSize * self.bytesPerSector * (numFat - 1)) | |
def FATEnd(self, numFat): | |
return self.FATStart(numFat+1) | |
@property | |
def FATSize(self): | |
return self.getBytes(36,4) | |
@property | |
def rootStart(self): | |
return self.FATStart(1) + (self.FATSize * self.numberOfFATs * self.bytesPerSector) | |
@property | |
def fsIdentityString(self): | |
return self.getString(82,8) | |
class ClEntry: | |
def __init__(self, offset, length, nextclidx, prevclidx=None): | |
self.offset = offset | |
self.length = length | |
self.next = nextclidx | |
self.prev = prevclidx | |
def __repr__(self): | |
return 'ClEnt(%s, %s, %s, %s)' % (self.offset, self.length, self.next, self.prev) | |
class Clusters: | |
def __init__(self, fs): | |
self.fs = fs | |
self.fat = [] | |
self.free = set() | |
self.fs.fs.seek(0, 2) | |
eof = self.fs.fs.tell() | |
for pos in range(self.fs.FATStart(1), self.fs.FATEnd(1), 4): | |
clidx = (pos - self.fs.FATStart(1)) / 4 | |
# not entirely sure why -2 is required here | |
offset = self.fs.rootStart + (clidx-2) * self.fs.bytesPerCluster | |
if offset + self.fs.bytesPerCluster >= eof: | |
break | |
nextcluster = self.fs.getBytes(pos, 4) | |
self.fat.append(ClEntry(offset, self.fs.bytesPerCluster, nextcluster)) | |
if nextcluster == 0: | |
self.free.add(clidx) | |
for clidx in xrange(0, len(self.fat)): | |
cluster = self.fat[clidx] | |
if cluster.next > 2 and cluster.next < 0xffffff8: | |
self.fat[cluster.next].prev = clidx | |
def setNextCluster(self, target, value): | |
if value is None: | |
value = 0 | |
if target is not None: | |
writeOffset = self.fs.FATStart(1) + target * 4 | |
self.fs.putUInt32(writeOffset, value) | |
self.fat[target].next = value | |
if value == 0: | |
# clear the previous cluster reference | |
self.fat[target].prev = None | |
# add cluster to the free list | |
self.free.add(target) | |
else: | |
if value < 0xffffff8: | |
# set the previous cluster reference | |
self.fat[value].prev = target | |
# remove cluster from the free list | |
self.free.discard(target) | |
def swap(self, clidx1, clidx2): | |
c1 = self.fat[clidx1] | |
c2 = self.fat[clidx2] | |
n1 = c1.next | |
n2 = c2.next | |
p1 = c1.prev | |
p2 = c2.prev | |
o1 = c1.offset | |
o2 = c2.offset | |
d1 = self.fs.getRawBytes(o1, c1.length) | |
d2 = self.fs.getRawBytes(o2, c2.length) | |
self.setNextCluster(p1, clidx2) | |
self.setNextCluster(clidx2, n1) | |
self.setNextCluster(p2, clidx1) | |
self.setNextCluster(clidx1, n2) | |
print o1 | |
print o2 | |
self.fs.putRawBytes(o1, d2) | |
self.fs.putRawBytes(o2, d1) | |
fs = Fat32(sys.argv[1]) | |
print "Bytes per sector:", ppNum(fs.bytesPerSector) | |
print "Sectors per cluster:", ppNum(fs.sectorsPerCluster) | |
print "Reserved sector count:", ppNum(fs.reservedSectorCount) | |
print "Size of FAT (sectors):", ppNum(fs.FATSize) | |
print "Number of FATs:", ppNum(fs.numberOfFATs) | |
print "Start of FAT1:", ppNum(fs.FATStart(1)) | |
print "Start of root directory:", ppNum(fs.rootStart) | |
print "Identity string:", fs.fsIdentityString | |
clusters = Clusters(fs) | |
if 0: | |
clusters.swap(4, 6) | |
clusters.fs.fs.flush() | |
sys.exit(0) | |
for arg in sys.argv[2:]: | |
clidx = clusters.fat[int(arg)].next | |
while clidx > 2 and clidx < 0xffffff8: | |
free = random.sample(clusters.free, 1)[0] | |
nextidx = clusters.fat[clidx].next | |
print 'swap %10s <=> %10s next %10s' % (clidx, free, nextidx) | |
clusters.swap(clidx, free) | |
clidx = nextidx | |
#print clusters.fat | |
#clusters.swap(5, 9) | |
#clusters.swap(6, 10) | |
clusters.fs.fs.flush() |
Regarding the fragmentation method: what theme was it written with in mind? Maximal fragmentation? Parity with natural fragmentation? Performance?
I could see this used in security research to emulate data that hides itself in dark drive space. Developing a model for what natural fragmentation looks like would help malware evade heuristics.
Themes, that is an interesting idea .. making one that could display ascii art into the older windows or dos defragmenter would be an interesting theme ...
That is a thing of beauty!
@FesterCluck Maximal fragmentation of a single file (It currently can't move the first cluster, though).
No jQuery :c.
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This is kinda silly but who knows, it might be usable for something. Maybe a defragmenter benchmark :)