Peter
/*
** This program tests your system to see if you have the lovely
** security-defeating semantics that an open with O_CREAT|O_EXCL
** set will successfully open a file named by a symbolic link that
** points to a non-existent file. Sadly, Posix is mute on what
** should happen in this situation.
**
** Results to date:
** AIX 3.2 OK
** BSD family OK
** BSD/OS 2.1 OK
** FreeBSD 2.1 OK
** DEC OSF/1 3.0 OK
** HP-UX 9.04 FAIL
** HP-UX 9.05 FAIL
** HP-UX 9.07 OK
** HP-UX 10.01 OK
** HP-UX 10.10 OK
** HP-UX 10.20 OK
** Irix 5.3 OK
** Irix 6.2 OK
** Linux OK
** NeXT 2.1 OK
** Solaris 2.x OK
** SunOS 4.x OK
** Ultrix 4.3 OK
*/
#include <stdio.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
char Attacker[128];
char Attackee[128];
main(argc, argv)
int argc;
char **argv;
{
struct stat st;
sprintf(Attacker, "/tmp/attacker.%d.%ld", getpid(), time(NULL));
sprintf(Attackee, "/tmp/attackee.%d.%ld", getpid(), time(NULL));
if (symlink(Attackee, Attacker) < 0)
{
printf("Could not create %s->%s symlink: %d\n",
Attacker, Attackee, errno);
bail(1);
}
(void) unlink(Attackee);
if (stat(Attackee, &st) >= 0)
{
printf("%s already exists -- remove and try again.\n",
Attackee);
bail(1);
}
if (open(Attacker, O_WRONLY|O_CREAT|O_EXCL, 0644) < 0)
{
int saveerr = errno;
if (stat(Attackee, &st) >= 0)
{
printf("Weird. Open failed but %s was created anyhow (errno = %d)\n",
Attackee, saveerr);
bail(1);
}
printf("Good show! Exclusive open works properly with symbolic links (errno = %d).\n",
saveerr);
bail(0);
}
if (stat(Attackee, &st) < 0)
{
printf("Weird. Open succeeded but %s was not created\n",
Attackee);
bail(2);
}
printf("Bad news: you can do an exclusive open through a symbolic link\n");
printf("\tBe sure you #define BOGUS_O_EXCL in conf.h\n");
bail(1);
}
bail(stat)
int stat;
{
(void) unlink(Attacker);
(void) unlink(Attackee);
exit(stat);
}
linux-2.0.28:
Good show! Exclusive open works properly with symbolic links (errno = 17).
linux-2.1.62:
Bad news: you can do an exclusive open through a symbolic link
Be sure you #define BOGUS_O_EXCL in conf.h