2.4.2 and 2.4.3 fail to test that kernel has MPPE support

[Anton Voronin <anton@chelcom.ru>]

Hi everyone,

I've got a problem with pppd-2.4.2 and 2.4.3 using MPPE with 2.4.x kernel.
The ccp_test() function from sys-linux.c returns -1, however kernel has MPPE 
support (ppp_mppe module gets loaded). With pppd-2.4.1, however, it works 
fine. While ccp_test() seems to be identical between versions 2.4.1 and 
2.4.2/2.4.3 of pppd, I noticed difference in the opt_buf argument supplied to 
ccp_test():

pppd-2.4.1:
===================
        if(p[5] & MPPE_40BIT) {
            keysize = 8;
            BCOPY(mppe_master_send_key_40, opt_buf+3, keysize);
            BCOPY(mppe_master_recv_key_40, opt_buf+11, keysize);
        } else if(p[5] & MPPE_128BIT) {
            keysize = 16;
            BCOPY(mppe_master_send_key_128, opt_buf+3, keysize);
            BCOPY(mppe_master_recv_key_128, opt_buf+19, keysize);
        }
        if(p[5] != 0) {
            opt_buf[0]=CI_MPPE;
            opt_buf[1]=CILEN_MPPE;
            opt_buf[2] = (go->mppe_stateless) ? 1 : 0;
            res = ccp_test(f->unit, opt_buf, (2*keysize)+3, 0);
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        } else {
            res = -1;
        }
===================

pppd-2.4.2/2.4.3:
===================
    if (go->mppe) {
        opt_buf[0] = CI_MPPE;
        opt_buf[1] = CILEN_MPPE;
        MPPE_OPTS_TO_CI(go->mppe, &opt_buf[2]);
        /* Key material unimportant here. */
        if (ccp_test(f->unit, opt_buf, CILEN_MPPE + MPPE_MAX_KEY_LEN, 0) <= 0) 
{
            error("MPPE required, but kernel has no support.");
            lcp_close(f->unit, "MPPE required but not available");
        }
    }
===================

In both cases opt_buf[0] and opt_buf[1] are filled identically.

However, in 2.4.1 only opt_buf[2] if filled, and then two keys are copied, 
while in 2.4.2/2.4.3 MPPE_OPTS_TO_CI() macro fills 4 more bytes of opt_buf (6 
bytes total), and none of the keys are copied behind them. But, the 3rd 
argument (option length) is set to CILEN_MPPE + MPPE_MAX_KEY_LEN (whilch is 
equal to 6 + 16 = 22). Seems like the rest 16 bytes are left uninitialized 
(even not zeroes, just contain garbage).

Is it a bug or I am using the wrong kernel patches, that behave differently? 
The file of patches I am using was called:

linux-2.4.20-openssl-0.9.6b-mppe.patch

Should this be something else?

Best regards,
-- 
Anton Voronin
Intersvyaz JSC
http://www.chelcom.ru
+7 (3512) 655199