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(ITS#6851) back-ldap assertion failure, LDAP proxy to Windows AD



Full_Name: Ted C. Cheng
Version: HEAD
OS: Redhat Linux
URL: ftp://ftp.openldap.org/incoming/
Submission from: (NULL) (75.80.56.88)


We encountered a back-ldap assertion failure with the back-ldap as a proxy to a
remote Active Directory on Windows 2003 R2. The assertion failure occurred when
the slapd  server was checking ACLs via the rwm overlay. Snippet of the stack
trace:

Thread 1 (Thread 32267):
....
#2  0x0000003c354296e6 in __assert_fail () from /lib64/libc.so.6
#3  0x00002ac57daaf6c1 in ldap_back_dobind_int (lcp=0x42f70170, op=0x42f702f0, 
   rs=0x42f700a0, sendok=LDAP_BACK_GETCONN, retries=0, dolock=1)
   at /home/build/sol-2.4.23.101221/sol24x/ldap24/servers/slapd/back-ldap/bind.c:1389
#4  0x00002ac57daafda0 in ldap_back_dobind (lcp=0x42f70170, op=0x42f702f0, 
   rs=0x42f700a0, sendok=LDAP_BACK_DONTSEND)
   at /home/build/sol-2.4.23.101221/sol24x/ldap24/servers/slapd/back-ldap/bind.c:1572
#5  0x00002ac57daac7a7 in ldap_back_entry_get (op=0x42f702f0, ndn=0x42f701d0, 
   oc=0x0, at=0x135ad370, rw=0, ent=0x42f70a58)

Analysis of the assertion failure:

The ldap_back_entry_get() function, back-ldap/search.c, is called for ACL
entries, via rwm overlay. The function sets op->o_do_not_cache to 1 before
calling into ldap_back_dobind():

       /* Tell getconn this is a privileged op */
       do_not_cache = op->o_do_not_cache;
       tag = op->o_tag;
       /* do not cache */
       op->o_do_not_cache = 1;
       /* ldap_back_entry_get() is an entry lookup, so it does not need
        * to know what the entry is being looked up for */
       op->o_tag = LDAP_REQ_SEARCH;
       rc = ldap_back_dobind( &lc, op, &rs, LDAP_BACK_DONTSEND ); 


The ldap_back_dobind() function calls ldap_back_dobind_int() for bind,
back-ldap/bind.c. The following ldap_back_dobind_int() code is destined for
assertion failure, if op->o_do_not_cache flag is set and there is no valid
binddn and bindcred returned by ldap_back_getconn(). Setting an invalid LDAP URI
for the remote AD Windows box is such a case.

	ldap_back_dobind_int(?)
	{
 		...
		if (sendok & LDAP_BACK_GETCONN) {
		?
			lc = ldap_back_getconn(op, rs, sendoff, &binddn, &bindcred);
			...
		}
		?

		if ( LDAP_BACK_CONN_ISIDASSERT( lc ) ) {
			if ( BER_BVISEMPTY( &binddn ) && BER_BVISEMPTY( &bindcred ) ) {
				/* if we got here, it shouldn't return result */
				rc = ldap_back_is_proxy_authz( op, rs,
						LDAP_BACK_DONTSEND, &binddn, &bindcred );

				/* ldap_back_is_proxy_authz always returns 0 when op->o_do_not_cache is set,
see below */
				assert( rc == 1 );------> assertion failure
			}
			rc = ldap_back_proxy_authz_bind( lc, op, rs, sendok,
				&binddn, &bindcred );
			?
		}
	}


When the op->o_do_not_cache flag is set, the ldap_back_is_proxy_authz() function
always returns 0.

	ldap_back_is_proxy_authz( ... )
	{
		...
		int             dobind = 0;

		if ( op->o_conn == NULL || op->o_do_not_cache ) {
			goto done;
		}
		...
	done:;
		return dobind; <--- always returns 0
	}



Ted C. Cheng
Symas Corporation