file permissions ignored

[hippocampe]

There is a file that I don't want opera to modify.

I did this in /home/hippocampe/.opera/:

 

rm filename

touch filename

chmod 444 filename

su

chown root:root filename

 

By then, nobody should be able to modify this file, let alone a program run by a normal user. But everytime I run opera (as normal user), this file is modified.

Is there something I missed here?

Thanks.

[Steve Scrimpshire]

try

 

chown your-username:users /usr/bin/opera

[hippocampe]

awww, didn't work :(

Is that how it's supposed to work? I thought file permissions for a user also apply for programs started by that user, otherwise it may cause a security problems?

[Steve Scrimpshire]

That's what I thought, too. I was just checking to see if that would work. Did you somehow put your user in the adm or root group? Open userdrake and check. You can choen opera back to root:root

[hippocampe]

I am not in a privileged user group as I checked in userdrake.

I am in cdrecording group (K3b did that).

I also cannot run priviledged commands as lsmod or ifconfig ... while in my regular user account.

[aru]

There is a file that I don't want opera to modify.  

I did this in /home/hippocampe/.opera/:

 

rm filename

touch filename

chmod 444 filename

su

chown root:root filename

 

By then, nobody should be able to modify this file, let alone a program run by a normal user. But everytime I run opera (as normal user), this file is modified.

How is modified?

is edited?

is totally re-wroten?

changes it's permissions?

changes it's owner?

 

Is there something I missed here?

Thanks.

 

Well, you didn't tell us what changes are made, but probably what is happening is that opera, runned by 'hippocampe' user, removes that file when it runs, and then creates a new copy of it.

 

An user is able to remove any file of his own directories, even if he hasn't permissions over it, or if the file is owned by others, included root. So as opera is launched by the user who owns the ~/.opera/ dir, it can remove and then re-create any file on that directory.

[hippocampe]

Oww, you're right!

Basically, what I wanted to do is replace that file with an empty one, set permissions to read only for everyone and change owner to root.

I thought that the file would be left empty this way.

I just tried to do the same thing with a dummy file and I was able to rm the file as regular user.

So, there is no way to tell opera to leave that file alone if I understand it?

:(

[qnr]

I'm not sure how this will work from an application, but you might try to change the attributes to immutable .... here's an example

 

root@linux:/home/terry# touch test.txt

root@linux:/home/terry# chattr +i test.txt

root@linux:/home/terry# rm test.txt

rm: remove write-protected file `test.txt'? y

rm: cannot unlink `test.txt': Operation not permitted

root@linux:/home/terry#

 

 

As you can see, not even root can delete it, until root does a chattr -i test.txt

[aru]

So, there is no way to tell opera to leave that file alone if I understand it?

:(

No as long as opera is runed by you; Everything you can do can be done by opera (I'm just talking about deleting files).

 

But there is some hope, as long as you use ext2 as your filesystem (I don't know if this will work with ext3, in reiserfs certainly not). For example, you can do:

~# touch foo

~# ls -l foo

-rw-r--r--    1 root     root            0 Feb 17 20:31 foo

~# chattr +i foo 

~# rm -f foo

rm: cannot remove `foo': Operation not permitted

~# ls -l foo

-rw-r--r--    1 root     root            0 Feb 17 20:31 foo

 

See, not even root is allowed to remove that file :wink:

 

(to remove it you should first "chattr -i" that file)

check the man pages of "chattr" and "lsattr" for more info

 

HTH

 

 

EDITED: Ooops! sorry you were faster

[Cannonfodder]

Here's a backward way of doing this that I just thought of.. write a script to

 

1. copy file to a hold file

2. run opera (let it modify whatnot)

3. copy hold file back to file

4. delete hold

 

You could probably expand it a bit so that if hold is there when you start, you replace the file first and then do steps 1-4.

 

When you want to run opera, you call the script.. would that do what you want?

[theYinYeti]

There was an old trick for Netscape, years ago. I don't remember why, some people wanted a file to remain empty in netscape's directory. The solution was to delete that file, and then to create a directory with the same name. So the directory cannot be deleted (unless the -r option is given to rm), nor can it be overwritten with a filename.

Maybe you can do something similar...

 

Yves.

[hippocampe]

Thanks guys,

First time i've seen the chattr command. It looks pretty powerful.

 

Unfortunately it doesn't work on a fs other than ext2 or ext3 :(

I get this on my xfs home partition:

chattr +i foo

chattr: Inappropriate ioctl for device while reading flags on foo