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Re: [nssldap] Question about getspnam/getpwnam and ldap

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Re: [nssldap] Question about getspnam/getpwnam and ldap
----- Original Message ----- From: "Buchan Milne" <bgmilne@mandriva.org> 
To: "Markus Moeller" <huaraz@moeller.plus.com>
Cc: <nssldap@padl.com>; <ldap-nis@padl.com>
Sent: Wednesday, January 09, 2008 4:24 PM
Subject: Re: [nssldap] Question about getspnam/getpwnam and ldap



On Wednesday 09 January 2008 15:03:07 Markus Moeller wrote:

Hi,

 I am looking into replacing NIS with LDAP and came to a point where I
still need to support getspnam/getpwnam for password checks as I have
legacy applications which can not be changed.
The question I have is how rfc 2307 is and should be enforced as I noticed 
differences between Linux and Solaris.  The rfc says:

   userPassword values which do not adhere to this syntax MUST NOT be
   used for authentication. The DUA MUST iterate through the values of
   the attribute until a value matching the above syntax is found. Only
   if encryptedpassword is an empty string does the user have no
   password. DUAs are not required to consider encryption schemes which
   the client will not recognize; in most cases, it may be sufficient to
   consider only "crypt".


Firstly does/should getspnam enforce "userPassword values which do not
adhere to this syntax MUST NOT be used for authentication" by rejecting
userpassword entries which don't follow rfc 2307 or is it up to the
application since the rfc states "DUAs are not required to consider
encryption schemes which the client will not recognize; in most cases, it 
may be sufficient to  consider only "crypt"." too (assuming getspnam in
nss_ldap is the DUA) ?  Solaris seems to enforce it in getspnam whereas
Linux doesn't.
Can you be more specific ? Do you mean you are using something besides clear 
(no encryption scheme identifier) or crypt, and seeing the password hash ?
The unixuserpassword attribute in AD does not use an encryption scheme identifier (but stores the crypt password). It has the same value as a "normal" /etc/shadow entry would have in the password field (e.g. 1c8n1k6cGDbSo).
A getent shadow markus (with markus being an ldap user in AD) gives on Linux: 
markus:1c8n1k6cGDbSo:13565::::::

and the following checkpass succeeds:

#include <sys/types.h>
#include <unistd.h>
#include <pwd.h>
#include <stdio.h>
#include <stdlib.h>
#include <shadow.h>
#include <crypt.h>
#include <string.h>

int main (int argc,char **argv)
{
   struct passwd *pwd_info;
   struct spwd *spwd_info;
   char *ct_passwd;
   char *enc_passwd;
   char *password;
   int i;

   if ( argc < 2) {
           exit(1);
   } else {
           if ((pwd_info = getpwnam(argv[1])) == NULL )  {
                 fprintf (stderr, "Call to getpwuid failed\n");
                 exit (1);
           }
   }

   for (i=0;i<3;i++) {
       ct_passwd = getpass("Enter password: ");

       if ((spwd_info = getspnam (pwd_info -> pw_name)) == NULL) {
fprintf (stderr, "Call to getspnam failed. Try password field from getpwnam\n"); 
           password=pwd_info->pw_passwd;
       } else {
           password=spwd_info->sp_pwdp;
       }
       enc_passwd = crypt (ct_passwd, password);

       if (strcmp (enc_passwd, password) == 0) {
           printf ("Passwords match.\n");
           break;
       } else
           printf ("Passwords don't match.\n");
   }

   return (0);
}
A getent shadow does not work on OpenSolaris. But the below test program (using OpenSolaris native nss_ldap libraries) gives: 
./test_shadow markus
passwd: name=markus
passwd: passwd=x
passwd: uid=500
passwd: gid=10000
passwd: gecos=Markus Moeller
passwd: homedir=/export/home/markus
passwd: shell=/bin/ksh


shadow: name=markus
shadow: passwd=*NP*
shadow: lastchg=-1(Wed Dec 31 01:00:00 1969)
shadow: min=-1
shadow: max=-1
shadow: warn=-1
shadow: inactive=-1
shadow: expire=-1(Wed Dec 31 01:00:00 1969)
If I modify the unixuserpassword value in AD from 1c8n1k6cGDbSo to {crypt}1c8n1k6cGDbSo OpenSolaris gives: 
./test_shadow markus
passwd: name=markus
passwd: passwd=x
passwd: uid=500
passwd: gid=10000
passwd: gecos=Markus Moeller
passwd: homedir=/export/home/markus
passwd: shell=/bin/ksh


shadow: name=markus
shadow: passwd=1c8n1k6cGDbSo
shadow: lastchg=-1(Wed Dec 31 01:00:00 1969)
shadow: min=-1
shadow: max=-1
shadow: warn=-1
shadow: inactive=-1
shadow: expire=-1(Wed Dec 31 01:00:00 1969)

and the checkpass succeeds too.

test_shadow.c
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <strings.h>
#include <pwd.h>
#include <shadow.h>

int main(int argc, char ** argv) {
   char *user=NULL;
   char *date=NULL,*dp;
   time_t time;
   struct passwd *pw=NULL;
   struct spwd *spw=NULL;

   if ( argc > 1 ) {
       user = argv[1];
   } else {
       exit(99);
   }

   pw = getpwnam(user);
   spw = getspnam(user);

   if ( pw ) {
       printf("passwd: name=%s\n",pw->pw_name);
       printf("passwd: passwd=%s\n",pw->pw_passwd);
       printf("passwd: uid=%d\n",pw->pw_uid);
       printf("passwd: gid=%d\n",pw->pw_gid);
       printf("passwd: gecos=%s\n",pw->pw_gecos);
       printf("passwd: homedir=%s\n",pw->pw_dir);
       printf("passwd: shell=%s\n",pw->pw_shell);
       printf("\n\n");
   }
   if ( spw ) {
       printf("shadow: name=%s\n",spw->sp_namp);
       printf("shadow: passwd=%s\n",spw->sp_pwdp);
       time=spw->sp_lstchg*3600*24;
       date=ctime(&time);
       if ((dp=strchr(date,'\n')) != NULL ) {
           *dp = '\0';
       }
       printf("shadow: lastchg=%ld(%s)\n",spw->sp_lstchg,date);
       printf("shadow: min=%d\n",spw->sp_min);
       printf("shadow: max=%d\n",spw->sp_max);
       printf("shadow: warn=%d\n",spw->sp_warn);
       printf("shadow: inactive=%d\n",spw->sp_inact);
       time=spw->sp_expire*3600*24;
       date=ctime(&time);
       if ((dp=strchr(date,'\n')) != NULL ) {
           *dp = '\0';
       }
       printf("shadow: expire=%d(%s)\n",spw->sp_expire,date);
   }

}
My problem is now that AD does not have the {crypt} prefix and Solaris requires it and I wanted to understand if the RFC is the reason for requiring the {crypt} prefix. From how I read it is optional.
At the end it may mean I have to use AD as a NIS server and not as an ldap server.
I tested with just {ssha}, and 'getent shadow bgmilne' did not show a hash: 

[root@tiger ~]# getent shadow bgmilne
bgmilne:*:12920::99999:7:::0

I added a {crypt} password (so I have both {ssha} and {crypt}), and
then 'getent shadow bgmilne' showed just the {crypt} hash in place of the *. 
I did not test clear text passwords (with no identifier).


Also Windows 2003 R2 uses unixuserpassword (this entry can
be synchronised with the Kerberos password in AD and is therefore
preferred) which does not follow rfc2307 as it contains the hash without
{crypt}.


Maybe they expect you to type the hash :-P.


The rfc states also:

  A DUA MAY utilise the attributes in the shadowAccount class to
   provide shadow password service (getspnam() and getspent()). In such
   cases, the DUA MUST NOT make use of the userPassword attribute for
   getpwnam() et al, and MUST return a non-matchable password (such as
   "x") to the client instead.

I noticed on Linux that provides the user with both the userpassword in
getpwnam and in getspnam.


I tested as follows:

$ perl -e 'my @foo = getpwnam("bgmilne");print "$foo[1]\n";'
and I get the password hash if the proxyuser (binddn in nss_ldap's ldap.conf) has read access to userPassword (which usually isn't required or desirable). 
Otherwise, I get:
[bgmilne@tiger ~]$ perl -e 'my @foo = getpwnam("bgmilne");print "$foo[1]\n";' 
*

If under these conditions, the rootbinddn has read access to userPassword,
root will still get the hash via getpwnam. I haven't tested with getspnam, as 
there is no perl builtin ...


Is that against RFC 2307 ? Does this mean a
getpwnam call need internally do a getspnam call to check if a password is 
provided before returning to the application ?


Please provide more information on how you arrive at your conclusions
(including your configuration - at least what the DNs you use for binddn and 
rootbinddn have read access to).
In the typical configuration, where the proxy user does not have read access 
to userPassword, it seems nss_ldap under Linux behaves (mostly) correctly.
In my case the proxy user has access to the userpassword attribute (unixuserpassword in AD) and my test_shadow test would give: 
./test_shadow markus
passwd: name=markus
passwd: passwd=1c8n1k6cGDbSo
passwd: uid=500
passwd: gid=10000
passwd: gecos=Markus Moeller
passwd: homedir=/export/home/markus
passwd: shell=/bin/ksh


shadow: name=markus
shadow: passwd=1c8n1k6cGDbSo
shadow: lastchg=-1(Wed Dec 31 01:00:00 1969)
shadow: min=-1
shadow: max=-1
shadow: warn=-1
shadow: inactive=-1
shadow: expire=-1(Wed Dec 31 01:00:00 1969)
and if I understand the rfc right getpwnam should return x and not the password. 



Regards,
Buchan



Regards
Markus