Create executable, automountable filesystem in a file, with password!

dd if=/dev/zero of=T bs=1024 count=10240;mkfs.ext3 -q T;E=$(echo 'read O;mount -o loop,offset=$O F /mnt;'|base64|tr -d '\n');echo "E=\$(echo $E|base64 -d);eval \$E;exit;">F;cat <(dd if=/dev/zero bs=$(echo 9191-$(stat -c%s F)|bc) count=1) <(cat T;rm T)>>F

This is just a proof of concept: A FILE WHICH CAN AUTOMOUNT ITSELF through a SIMPLY ENCODED script. It takes advantage of the OFFSET option of mount, and uses it as a password (see that 9191? just change it to something similar, around 9k). It works fine, mounts, gets modified, updated, and can be moved by just copying it. USAGE: SEE SAMPLE OUTPUT The file is composed of three parts: a) The legible script (about 242 bytes) b) A random text fill to reach the OFFSET size (equals PASSWORD minus 242) c) The actual filesystem Logically, (a)+(b) = PASSWORD, that means OFFSET, and mount uses that option. PLEASE NOTE: THIS IS NOT AN ENCRYPTED FILESYSTEM. To improve it, it can be mounted with a better encryption script and used with encfs or cryptfs. The idea was just to test the concept... with one line :) It applies the original idea of http://www.commandlinefu.com/commands/view/7382/command-for-john-cons for encrypting the file. The embedded bash script can be grown, of course, and the offset recalculation goes fine. I have my own version with bash --init-file to startup a bashrc with a well-defined environment, aliases, variables.

Sample Output

Use at your own risk.

# dd if=/dev/zero of=T bs=1024 count=10240;mkfs.ext3 -q T;E=$(echo 'read O;mount -o loop,offset=$O F /mnt;'|base64|tr -d '\n');  echo "E=\$(echo $E|base64 -d);eval \$E;exit;">F;cat <(dd if=/dev/zero bs=$(echo 9191-$(stat -c%s F)|bc) count=1) <(cat T;rm    T)>>F
10240+0 records in
10240+0 records out
10485760 bytes (10 MB) copied, 0.127043 s, 82.5 MB/s
T is not a block special device.
Proceed anyway? (y,n) y
1+0 records in
1+0 records out
9104 bytes (9.1 kB) copied, 0.000116352 s, 78.2 MB/s

(before executing next, make sure /mnt is empty and has nothing mounted, otherwise you can lose files)

# bash F
9191
(I entered 9191, is the password, can be modified in the script)

# l /mnt/
drwx------ 2 root root 12K Jan 31 02:33 lost+found/

# df -h
Filesystem        Size  Used Avail Use% Mounted on
...
/dev/loop0        9.7M  1.1M  8.1M  12% /mnt

# mount
...
/root/F on /mnt type ext3 (rw,relatime,data=ordered)

# umount /mnt 

# head -1 F
E=$(echo cmVhZCBPO21vdW50IC1vIGxvb3Asb2Zmc2V0PSRPIEYgL21udDsK|base64 -d);eval $E;exit;

# E=$(echo cmVhZCBPO21vdW50IC1vIGxvb3Asb2Zmc2V0PSRPIEYgL21udDsK|base64 -d);echo $E
(changed eval x echo)
read O;mount -o loop,offset=$O F /mnt;

By: rodolfoap

2013-01-31 01:38:30

cat dd echo mkfs.ext3 mount rm stat tr Filesystem Security mount Encryption encoding

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What Others Think

doesnt seem to work on ubunbu, bash F just hangs

chrismccoy · 618 weeks and 1 day ago

Chrismccoy: It's probably not hanging, but asking you for the offset. If not, just follow the procedure (sample output) to confirm it generated the executable base64 encoder header correctly. I'ts really simple...

rodolfoap · 618 weeks and 1 day ago

(executable base64 encodeD header)

rodolfoap · 618 weeks and 1 day ago

head -1 F shows the exact same as yours, then the next part root@sorry:/home/chris# read O;mount -o loop,offset=$O F /mnt; mount: invalid offset '' specified

chrismccoy · 618 weeks ago

nm got it working ;)

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What do you think?

Any thoughts on this command? Does it work on your machine? Can you do the same thing with only 14 characters?

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