Bug 1250605

Created attachment 1059482 [details]
ausearch after conmand service start

conman uses freeipmi library when it needs to talk over IPMI.
freeipmi library contains this code snippet:

int
ipmi_get_random (void *buf, unsigned int buflen)
{
#if (HAVE_DEVURANDOM || HAVE_DEVRANDOM)
  int fd, rv;
#endif /* !(HAVE_DEVURANDOM || HAVE_DEVRANDOM) */

  if (!buf)
    {
      SET_ERRNO (EINVAL);
      return (-1);
    }

  if (!buflen)
    return (0);

#if (HAVE_DEVURANDOM || HAVE_DEVRANDOM)
#if HAVE_DEVURANDOM
  if ((fd = open ("/dev/urandom", O_RDONLY)) < 0)
    goto gcrypt_rand;
#else  /* !HAVE_DEVURANDOM */
  if ((fd = open ("/dev/random", O_RDONLY)) < 0)
    goto gcrypt_rand;
#endif /* !HAVE_DEVURANDOM */

  if ((rv = read (fd, buf, buflen)) < buflen)
    {
      close (fd);
      goto gcrypt_rand;
    }

  /* ignore potential error, cleanup path */
  close (fd);
  return (rv);
#endif /* !(HAVE_DEVURANDOM || HAVE_DEVRANDOM) */

 gcrypt_rand:
/* achu: nothing to do with encryption, but the gcrypt lib isn't loaded.
 * hopefully the user has /dev/random or /dev/urandom.
 */
#ifdef WITH_ENCRYPTION
  gcry_randomize ((unsigned char *)buf, buflen, GCRY_STRONG_RANDOM);
  return (buflen);
#else /* !WITH_ENCRYPTION */
  SET_ERRNO (EPERM);
  return (-1);
#endif /* !WITH_ENCRYPTION */
}

As you see, when open("/dev/[u]random") doesn't succeed, it falls back to gcry_randomize(), which is provided by libgcrypt library.

Unfortunately, gcry_randomize() fares no better. After several layers of abstraction, we reach this function which again tries to access /dev/[u]random, and when that doesn't work, it fatally fails:

static int (*
getfnc_gather_random (void))(void (*)(const void*, size_t,
                                      enum random_origins),
                             enum random_origins, size_t, int)
{
  int (*fnc)(void (*)(const void*, size_t, enum random_origins),
             enum random_origins, size_t, int);

#if USE_RNDLINUX
  if ( !access (NAME_OF_DEV_RANDOM, R_OK)
       && !access (NAME_OF_DEV_URANDOM, R_OK))
    {
      fnc = _gcry_rndlinux_gather_random;
      return fnc;
    }
#endif

#if USE_RNDEGD
  if ( _gcry_rndegd_connect_socket (1) != -1 )
    {
      fnc = _gcry_rndegd_gather_random;
      return fnc;
    }
#endif

#if USE_RNDUNIX
  fnc = _gcry_rndunix_gather_random;
  return fnc;
#endif

#if USE_RNDW32
  fnc = _gcry_rndw32_gather_random;
  return fnc;
#endif

#if USE_RNDW32CE
  fnc = _gcry_rndw32ce_gather_random;
  return fnc;
#endif

  log_fatal (_("no entropy gathering module detected\n"));

  return NULL; /*NOTREACHED*/
}

log_fatal() ends up calling abort() and kills itself with SIGABRT.

Could you re-test it with latest policy? The access to /dev/urandom should be allowed without a need to enable any boolean:

# rpm -qa selinux-policy\*
selinux-policy-targeted-3.13.1-37.el7.noarch
selinux-policy-3.13.1-37.el7.noarch
selinux-policy-devel-3.13.1-37.el7.noarch
selinux-policy-minimum-3.13.1-37.el7.noarch
selinux-policy-mls-3.13.1-37.el7.noarch
selinux-policy-sandbox-3.13.1-37.el7.noarch
selinux-policy-doc-3.13.1-37.el7.noarch
# sesearch -s conman_t -t urandom_device_t -A -C
Found 3 semantic av rules:
   allow domain urandom_device_t : chr_file { ioctl read getattr lock open } ; 
DT allow nsswitch_domain urandom_device_t : chr_file { ioctl read getattr lock open } ; [ authlogin_nsswitch_use_ldap ]
DT allow domain urandom_device_t : chr_file { ioctl read getattr lock open } ; [ global_ssp ]
#

I can confirm that it works as expected with 3.13.1-37 policy. Thanks Milos.

# rpm -qa selinux-policy\*
selinux-policy-3.13.1-37.el7.noarch
selinux-policy-devel-3.13.1-37.el7.noarch
selinux-policy-targeted-3.13.1-37.el7.noarch
# rpm -q conman freeipmi
conman-0.2.7-12.el7.ppc64
freeipmi-1.2.9-7.el7.ppc64

# systemctl start conman
# systemctl status conman
conman.service - ConMan Console Management Daemon
   Loaded: loaded (/usr/lib/systemd/system/conman.service; disabled)
   Active: active (running) since Thu 2015-08-06 05:47:56 EDT; 6s ago
  Process: 12681 ExecStart=/usr/sbin/conmand -c /etc/conman.conf (code=exited, status=0/SUCCESS)
 Main PID: 12683 (conmand)
   CGroup: /system.slice/conman.service
           └─12683 /usr/sbin/conmand -c /etc/conman.conf

systemd[1]: Started ConMan Console Management Daemon.

# conman ipmisol

<ConMan> Connection to console [ipmisol] opened.

Hi,

(hopefully this won't re-open the bug as it's not really a problem, but would appreciate an answer anyway)

I can't see the diff, but here's what I have on a 7.1 system:
> # sesearch -s conman_t -t urandom_device_t -A -C
> Found 2 semantic av rules:
> ... nss ...
> DT allow domain urandom_device_t : chr_file { ioctl read getattr lock open } ; [ global_ssp ]

And here's what you linked:
> # sesearch -s conman_t -t urandom_device_t -A -C
> Found 3 semantic av rules:
>   allow domain urandom_device_t : chr_file { ioctl read getattr lock open } ; 
> ... nss ...
> DT allow domain urandom_device_t : chr_file { ioctl read getattr lock open } ; [ global_ssp ]


Looking at the source (from selinux-policy-3.13.1-44.el7.src.rpm, 7.2 beta...), we have ./policy/modules/kernel/domain.te:
# Allow all domains to read /dev/urandom. It is needed by all apps/services
# linked to libgcrypt. There is no harm to allow it by default.
dev_read_urand(domain)

then a few lines below:
tunable_policy(`global_ssp',`
        # enable reading of urandom for all domains:
        # this should be enabled when all programs
        # are compiled with ProPolice/SSP
        # stack smashing protection.
        dev_read_urand(domain)
')

Sooo. Why not just make the tunable default to on? Or remove the bool? It looks to me that it just became useless, but I may have missed something.


Thanks,
-- 
Dominique Martinet

Yes, we will remove it in 7.3.

Thank you.

Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.

For information on the advisory, and where to find the updated
files, follow the link below.

If the solution does not work for you, open a new bug report.

https://rhn.redhat.com/errata/RHBA-2015-2300.html