On Tue, Oct 12, 2010 at 12:41:04AM +0400, Dmitry-T wrote:
quoted text > I'm install OpenBSD 4.7 (dmesg attached)
>
> uname -a
> OpenBSD d1.my.domain 4.7 GENERIC#112 amd64
>
> Run as root:
> dd if=/dev/wd0c of=/dev/null bs=1m &
> dd if=/dev/wd0c of=/dev/null bs=1m &
> dd if=/dev/wd0c of=/dev/null bs=1m &
>
> top
>
> load averages: 3.12, 2.50, 1.49 16:54:08
> 37 processes: 36 idle, 1 on processor
> CPU states: 0.1% user, 0.0% nice, 7.3% system, 3.6% interrupt, 89.1% idle
> Memory: Real: 35M/339M act/tot Free: 2393M Swap: 0K/3071M used/tot
>
> PID USERNAME PRI NICE SIZE RES STATE WAIT TIME CPU COMMAND
> 754 root -14 0 2232K 1228K sleep inode 0:24 6.10% dd
> 25914 root -5 0 2216K 1224K sleep getblk 0:24 6.05% dd
> 21919 root -14 0 2204K 1224K sleep inode 2:08 5.96% dd
>
> iostat wd0 1
>
> tty wd0 cpu
> tin tout KB/t t/s MB/s us ni sy in id
> 0 0 2.00 5141 10.04 0 0 23 13 64
> 0 0 2.00 5021 9.81 0 0 16 10 74
> 0 299 2.00 5206 10.17 0 0 21 8 71
> 0 0 2.00 5066 9.90 0 0 15 8 77
>
>
> Run as _normal user_:
> dd if=/dev/urandom of=/dev/null
>
> Try to recover ballance:
> renice 20 -p 30996
> renice -20 -p 21919 25914 754
^^^^^
If you run any cpu bound process with priority -20, you will give all
the cpu to that process, without giving any chance to other processes
to run, so your box will hang until it terminates. This requires root
privileges.
quoted text >
> It is not secure. One user script or program may load CPU and
> database or another servers lost speed in disk operations.
> This is hole for DOS attacks in OpenBSD design.
Yeah, this is an attack root can do by renicing a cpu bound process,
but ``rm -rf /'' is much easier, isn't it?
-- Alexandre
