[SOLVED] Can no remove symlinks, Busybox SSH shell

dorsio · 08-06-2014, 07:34 PM

Can no remove symlinks: after rebooting device, symlinks appears again.
BusyBox SSH shell. These symlinks already existed, created by firmware.

Code:

login as: root
cd /nvram/1/security/
 ls
ab_cd.cer       mk_ehce.cer       efg_hr.cer      zooe_lsu.bin
download          fr_lkoy.bin    bkm_lua.bin

 ls -la
total 4
drwxr-xr-x    3 root     0                0 Jan  1 00:00 .
drwxr-xr-x    5 root     0                0 Jan  1 00:00 ..
-rwxrwxrwx    1 root     0              905 Jan  1 00:02 ab_cd.cer
drwxr-xr-x    2 root     0                0 Jan  1 00:00 download
lrwxrwxrwx    1 root     0               25 Jan  1 00:00 mk_ehce.cer -> /nvram/fw/bdm/mk_ehce.cer
lrwxrwxrwx    1 root     0               28 Jan  1 00:00 fr_lkoy.bin -> /nvram/fw/bdm/fr_lkoy.bin
-rwxrwxrwx    1 root     0             1052 Jan  1 00:02 efg_hr.cer
-rwxrwxrwx    1 root     0              140 Jan  1 00:02 bkm_lua.bin
lrwxrwxrwx    1 root     0               37 Jan  1 00:00 zooe_lsu.bin -> /etc/docsis/security/zooe_lsu.bin


rm mk_ehce.cer
rm fr_lkoy.bin

cd /nvram/fw/bdm/
ls -la

total 0
drwxr-xr-x    2 root     0                0 Jan  1 00:10 .
drwxr-xr-x    4 root     0                0 Aug  5  2014 ..

cd /nvram/1/security/

ls -la

total 4
drwxr-xr-x    3 root     0                0 Jan  1 00:07 .
drwxr-xr-x    5 root     0                0 Jan  1 00:00 ..
-rwxrwxrwx    1 root     0              905 Jan  1 00:02 ab_cd.cer
drwxr-xr-x    2 root     0                0 Jan  1 00:00 download
-rwxrwxrwx    1 root     0             1052 Jan  1 00:02 efg_hr.cer
-rwxrwxrwx    1 root     0              140 Jan  1 00:02 bkm_lua.bin
lrwxrwxrwx    1 root     0               37 Jan  1 00:00 zooe_lsu.bin -> /etc/docsis/security/zooe_lsu.bin


After rebooting:

cd /nvram/1/security/
ls -la
total 4
drwxr-xr-x    3 root     0                0 Jan  1 00:00 .
drwxr-xr-x    5 root     0                0 Jan  1 00:00 ..
-rwxrwxrwx    1 root     0              905 Jan  1 00:02 ab_cd.cer
drwxr-xr-x    2 root     0                0 Jan  1 00:00 download
lrwxrwxrwx    1 root     0               25 Jan  1 00:00 mk_ehce.cer -> /nvram/fw/bdm/mk_ehce.cer
lrwxrwxrwx    1 root     0               28 Jan  1 00:00 fr_lkoy.bin -> /nvram/fw/bdm/fr_lkoy.bin
-rwxrwxrwx    1 root     0             1052 Jan  1 00:02 efg_hr.cer
-rwxrwxrwx    1 root     0              140 Jan  1 00:02 bkm_lua.bin
lrwxrwxrwx    1 root     0               37 Jan  1 00:00 zooe_lsu.bin -> /etc/docsis/security/zooe_lsu.bin

Firerat · 08-07-2014, 02:22 PM

So find what is creating those symlinks..

But.. why are they a problem?
Why do you feel you need to remove them/

jefro · 08-07-2014, 04:17 PM

My guess is that busybox is a compiled package. You'd have to rebuild it to remove any references.

Firerat · 08-07-2014, 04:52 PM

They don't look like busybox symlinks

dorsio · 08-07-2014, 04:56 PM

I think I managed to deal with this issue: this symlinks are actually firmware feature, firmware does not allow to remove or rename them, and file names are predefined. I needed to replace those files (first removing them). When files are properly named, they all are symlinks.

Firerat · 08-07-2014, 05:54 PM

You might find that it is some kind of initfs

As an example, an android boot image is the kernel and initfs 'packaged' together

In order to make a permanent adjustment you have to 'unpack', then unpack the initfs,, modify .. recreate initfs and finally repackage

I don't know what your device is..
See if you can work out the boot process
Maybe someone else already has?

jefro · 08-07-2014, 10:20 PM

This is some kind of modem or router.

dorsio · 08-08-2014, 08:17 AM

that's cable modem. I have no goal to rewrite the code, I just trying to figure how to replace the files properly. Sometimes I got ready symlinks after uploading new files, sometimes it does not. I have no source code. I can manage boot process via console, and can view file system via SFTP.

Firerat · 08-08-2014, 08:47 AM

the question is "Why are you trying to modify the symlinks?"

I think if you succeed your cable modem will no longer function correctly

dorsio · 08-08-2014, 11:56 AM

Quote:

Originally Posted by Firerat

the question is "Why are you trying to modify the symlinks?"

I think if you succeed your cable modem will no longer function correctly

I need replace files, that's all. The files intended to be replaceable, I know this. I need to remove old and upload new files. I find that one of the files can not be downoaded. That's strange, is that something related to linux permissions? When I remove files from ssh, I remove only symlinks, not actual files? Where then actual files stored? (as symlinks are restored after reboot).

Firerat · 08-08-2014, 12:00 PM

ok, so replace the file which the symlink points to

don't replace
/nvram/1/security/zooe_lsu.bin

instead replace
/etc/docsis/security/zooe_lsu.bin

dorsio · 08-08-2014, 12:32 PM

To remove files which are symlinks, should I use
rm mk_ehce.cer or

rm /nvram/fw/bdm/mk_ehce.cer?

Firerat · 08-08-2014, 12:58 PM

No.

There is no need to remove the symlinks

If you want to change the 'content of a symlink' then change the file the symlink points to

BUT before you go breaking your cable modem , learn the basics first.

As you do not understand what a symlink is I do not believe you are competent enough.,

But hey ... we learn faster from our mistakes .. so feel free to brick that cable modem.

Out of interest, , what is your end goal here (please don't say replace symlinks )

Are you trying to make it faster? More secure?

What is all this effot for?

dorsio · 08-08-2014, 03:38 PM

Mainly for testing and researching, for improving it. That's test device. I know what is symlinks. But the Linux isn't what I know well. I flashed device more than once, successfully, and didn't brick it. Removing/replacing symlinks can not brick cable modem.

Firerat · 08-08-2014, 04:58 PM

You know this because you removed the symlinks and they reappeared?

You are probably right, no permo-brick, maybe 'soft'brick

If you understand what symlinks are.. why this thread?

Please understand, I don't wish to be combative

I'm not familiar with your device, and your goal is too 'open'
I think you need to seek advice from people experienced with your device

What is the device?
have you searched for forums specifically related to hacking that device?

I've given the answer to your symlink problem, replace the files the symlinks link to.
You say you understand symlinks,

If that is true.. this thread is solved, mark it as such!