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SubjectRe: NT vulnerable to attack on CPU

bofh@snoopy.virtual.net.au wrote:
> I have written and run test programs such as that and not had any problems.
> Your oops indicates that there is some bug in process handling in the kernel
> you are running. Other versions of the Linux kernel do not have this bug.

Yes. When I ran the "wabbit" under 2.0.27, there were no oopses. The
system slowed down greatly (to the point of being unusable) as the load
average went up to 150 or so, but after I pressed control-c, everything
returned to normal.

> for users. So I could set my system up so that the following command would
> result in fork failing if the user already has 20 or more processes:
>#echo 20 > /proc/sys/procs-per-user
>
> What do you think?

That sounds ideal.

> It doesn't. Use lshell and it'll work for all shells.

My /etc/lshell.conf has this:

root - // No limits for root
default C60P30D20F24 // Default limits, 60 min's CPU time, 30
processes, 20Mb, 24 file descriptors

but I haven't configured it to run. Instead, I'm using the shadow suite,
and /etc/limits contained:

# Format:
# <username> <limits-string>
#
# default entry is '*' for username
#
# Valid flags are:
# C: max core file size (KB)
# D: max data size (KB)
# F: maximum filesize (KB)
# M: max locked-in-memory address space (KB)
# N: max number of open files
# R: max resident set size (KB)
# S: max stack size (KB)
# T: max CPU time (MIN)
# U: max number of processes
# L: max number of logins for this user
#
# the default entry
#* L2 D6144 R2048 S2048 U32 N32 F16384 T5 C0
L12 D8192 R16384 S4096 U32 N64 C0
# another way of suspending a user login
nobody L0
# this account has no limits
root -

which was misconfigured (I'd forgotten the asterisk for the default
entry), so the "limit" command in tcsh (from my own account) returned:

cputime unlimited
filesize 1048576 kbytes
datasize unlimited
stacksize 8192 kbytes
coredumpsize 0 kbytes
memoryuse unlimited
descriptors 256
memorylocked unlimited
maxproc 256

under 2.0.27. Under 2.1.17, it looks the same, except that I'd applied
Jared Mauch's patch to fd.c and limits.h, increasing the number of open
file descriptors to 512.

After adding the asterisk to /etc/limits, I could run the fork bomb from
my own account with no problems. The summary from "top":

11:56pm up 29 min, 2 users, load average: 24.30, 8.21, 3.69
52 processes: 20 sleeping, 32 running, 0 zombie, 0 stopped
CPU states: 4.2% user, 95.6% system, 99.1% nice, 0.9% idle
Mem: 62668K av, 12356K used, 50312K free, 10504K shrd, 872K buff
Swap: 0K av, 0K used, 0K free 7300K cached

Here's my configuration for 2.1.17:

CONFIG_EXPERIMENTAL=y
CONFIG_MODULES=y
CONFIG_MODVERSIONS=y
CONFIG_KERNELD=y
CONFIG_NET=y
CONFIG_PCI=y
CONFIG_PCI_OPTIMIZE=y
CONFIG_SYSVIPC=y
CONFIG_BINFMT_AOUT=m
CONFIG_BINFMT_ELF=y
CONFIG_BINFMT_JAVA=m
CONFIG_M486=y
CONFIG_BLK_DEV_FD=m
CONFIG_BLK_DEV_IDE=y
CONFIG_BLK_DEV_IDEDISK=y
CONFIG_BLK_DEV_LOOP=m
CONFIG_INET=y
CONFIG_PATH_MTU_DISCOVERY=y
CONFIG_IP_NOSR=y
CONFIG_IPV6=m
CONFIG_LLC=y
CONFIG_SCSI=m
CONFIG_CHR_DEV_ST=m
CONFIG_BLK_DEV_SR=m
CONFIG_BLK_DEV_SR_VENDOR=y
CONFIG_SCSI_CONSTANTS=y
CONFIG_SCSI_AHA1542=m
CONFIG_NETDEVICES=y
CONFIG_NET_ETHERNET=y
CONFIG_NET_ISA=y
CONFIG_NE2000=m
CONFIG_PPP=y
CONFIG_SHAPER=m
CONFIG_MINIX_FS=m
CONFIG_EXT2_FS=y
CONFIG_FAT_FS=y
CONFIG_MSDOS_FS=m
CONFIG_VFAT_FS=m
CONFIG_UMSDOS_FS=m
CONFIG_PROC_FS=y
CONFIG_NFS_FS=m
CONFIG_SMB_FS=m
CONFIG_SMB_WIN95=y
CONFIG_ISO9660_FS=m
CONFIG_SERIAL=y
CONFIG_PRINTER=m
CONFIG_SOUND=m
CONFIG_SB=y
CONFIG_ADLIB=y
CONFIG_YM3812=y
CONFIG_LOWLEVEL_SOUND=y
CONFIG_AWE32_SYNTH=y
___
Trevor Johnson <trevor@jpj.net>



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