Re: Reserved Blocks

[Oleg Drokin <green@namesys.com>]

Hello!

On Mon, Sep 16, 2002 at 05:15:20PM +0400, Nikita Danilov wrote:

> What I thought about is adding new mount option -o root_blk=1000, and
> adding one `if' statement to the
> fs/reiserfs/bitmap.c:reiserfs_allocate_blocknrs().

Actually two mount options. Or even three.
One option is to specify uid for whom to reserve. Or may be not uid but gid,
too.

> Also, if there are not enough free blocks at the -mount- time---issue a
> warning. What about this? Oleg?

Sounds easy enough.

But is easily defeated, unfortunatelly.
Since the spans across already allocated blocks without any control,
the only moment root-owned process makes tree to occupy one more block to
create some directory, for example, malicious process immediately writes
file tail into that free space...

>  > >  > Is this essential UNIX filesystem feature implemented?
>  > > Well, nobody asked for it yet. :)
>  > Allow me to ask on behalf of all the SysAdmins out there.  This is an
>  > extremely useful standard safeguard against users filling up /var (or,

No. It does not work, I think. Well, it works, but can be easily defeated.

E.g. if I need to overflow your partition where logs are stored, I'd do someting
like that:
while :; do cat /etc/passwd | logger -t nobody ; done
Repeat with different -p swithces if you have several filesystems for different
logs.

Also consider there is set uid application that outputs data.
I just do setuid_app >>/fs_to_fill/somefile
and repeat it that much times to fill the fs.

So this protection you are asking for is mostly imagenary.

>  > Perhaps you should have a section in your FAQ that covers
>  > standard/traditional filesystem features not present in ReiserFS, or
>  > at what kernel version they were merged in - eg 2.4.19pre3 for inode
>  > attributes, and not yet for Filesystem Quotas or SuperUser Reserved
>  > Blocks percentage.

FS quotas are implemented. Link to URL is in our FAQ.

Bye,
    Oleg