#include "k5-int.h"
#include "auth_con.h"
+static krb5_boolean chk_heimdal_seqnum(krb5_ui_4, krb5_ui_4);
+
static krb5_error_code
actx_copy_addr(krb5_context context, const krb5_address *inad, krb5_address **outad)
{
*data = auth_context->checksum_func_data;
return 0;
}
+
+/*
+ * krb5int_auth_con_chkseqnum
+ *
+ * We use a somewhat complex heuristic for validating received
+ * sequence numbers. We must accommodate both our older
+ * implementation, which sends negative sequence numbers, and the
+ * broken Heimdal implementation (at least as of 0.5.2), which
+ * violates X.690 BER for integer encodings. The requirement of
+ * handling negative sequence numbers removes one of easier means of
+ * detecting a Heimdal implementation, so we resort to this mess
+ * here.
+ *
+ * X.690 BER (and consequently DER, which are the required encoding
+ * rules in RFC1510) encode all integer types as signed integers.
+ * This means that the MSB being set on the first octet of the
+ * contents of the encoding indicates a negative value. Heimdal does
+ * not prepend the required zero octet to unsigned integer encodings
+ * which would otherwise have the MSB of the first octet of their
+ * encodings set.
+ *
+ * Our ASN.1 library implements a special decoder for sequence
+ * numbers, accepting both negative and positive 32-bit numbers but
+ * mapping them both into the space of positive unsigned 32-bit
+ * numbers in the obvious bit-pattern-preserving way. This maintains
+ * compatibility with our older implementations. This also means that
+ * encodings emitted by Heimdal are ambiguous.
+ *
+ * Heimdal counter value received uint32 value
+ *
+ * 0x00000080 0xFFFFFF80
+ * 0x000000FF 0xFFFFFFFF
+ * 0x00008000 0xFFFF8000
+ * 0x0000FFFF 0xFFFFFFFF
+ * 0x00800000 0xFF800000
+ * 0x00FFFFFF 0xFFFFFFFF
+ * 0xFF800000 0xFF800000
+ * 0xFFFFFFFF 0xFFFFFFFF
+ *
+ * We use two auth_context flags, SANE_SEQ and HEIMDAL_SEQ, which are
+ * only set after we can unambiguously determine the sanity of the
+ * sending implementation. Once one of these flags is set, we accept
+ * only the sequence numbers appropriate to the remote implementation
+ * type. We can make the determination in two different ways. The
+ * first is to note the receipt of a "negative" sequence number when a
+ * "positive" one was expected. The second is to note the receipt of
+ * a sequence number that wraps through "zero" in a weird way. The
+ * latter corresponds to the receipt of an initial sequence number in
+ * the ambiguous range.
+ *
+ * There are 2^7 + 2^15 + 2^23 + 2^23 = 16810112 total ambiguous
+ * initial Heimdal counter values, but we receive them as one of 2^23
+ * possible values. There is a ~1/256 chance of a Heimdal
+ * implementation sending an intial sequence number in the ambiguous
+ * range.
+ *
+ * We have to do special treatment when receiving sequence numbers
+ * between 0xFF800000..0xFFFFFFFF, or when wrapping through zero
+ * weirdly (due to ambiguous initial sequence number). If we are
+ * expecting a value corresponding to an ambiguous Heimdal counter
+ * value, and we receive an exact match, we can mark the remote end as
+ * sane.
+ */
+krb5_boolean
+krb5int_auth_con_chkseqnum(
+ krb5_context ctx,
+ krb5_auth_context ac,
+ krb5_ui_4 in_seq)
+{
+ krb5_ui_4 exp_seq;
+
+ exp_seq = ac->remote_seq_number;
+
+ /*
+ * If sender is known to be sane, accept _only_ exact matches.
+ */
+ if (ac->auth_context_flags & KRB5_AUTH_CONN_SANE_SEQ)
+ return in_seq == exp_seq;
+
+ /*
+ * If sender is not known to be sane, first check the ambiguous
+ * range of received values, 0xFF800000..0xFFFFFFFF.
+ */
+ if ((in_seq & 0xFF800000) == 0xFF800000) {
+ /*
+ * If expected sequence number is in the range
+ * 0xFF800000..0xFFFFFFFF, then we can't make any
+ * determinations about the sanity of the sending
+ * implementation.
+ */
+ if ((exp_seq & 0xFF800000) == 0xFF800000 && in_seq == exp_seq)
+ return 1;
+ /*
+ * If sender is not known for certain to be a broken Heimdal
+ * implementation, check for exact match.
+ */
+ if (!(ac->auth_context_flags & KRB5_AUTH_CONN_HEIMDAL_SEQ)
+ && in_seq == exp_seq)
+ return 1;
+ /*
+ * Now apply hairy algorithm for matching sequence numbers
+ * sent by broken Heimdal implementations. If it matches, we
+ * know for certain it's a broken Heimdal sender.
+ */
+ if (chk_heimdal_seqnum(exp_seq, in_seq)) {
+ ac->auth_context_flags |= KRB5_AUTH_CONN_HEIMDAL_SEQ;
+ return 1;
+ }
+ return 0;
+ }
+
+ /*
+ * Received value not in the ambiguous range? If the _expected_
+ * value is in the range of ambiguous Hemidal counter values, and
+ * it matches the received value, sender is known to be sane.
+ */
+ if (in_seq == exp_seq) {
+ if (( exp_seq & 0xFFFFFF80) == 0x00000080
+ || (exp_seq & 0xFFFF8000) == 0x00008000
+ || (exp_seq & 0xFF800000) == 0x00800000)
+ ac->auth_context_flags |= KRB5_AUTH_CONN_SANE_SEQ;
+ return 1;
+ }
+
+ /*
+ * Magic wraparound for the case where the intial sequence number
+ * is in the ambiguous range. This means that the sender's
+ * counter is at a different count than ours, so we correct ours,
+ * and mark the sender as being a broken Heimdal implementation.
+ */
+ if (exp_seq == 0
+ && !(ac->auth_context_flags & KRB5_AUTH_CONN_HEIMDAL_SEQ)) {
+ switch (in_seq) {
+ case 0x100:
+ case 0x10000:
+ case 0x1000000:
+ ac->auth_context_flags |= KRB5_AUTH_CONN_HEIMDAL_SEQ;
+ exp_seq = in_seq;
+ return 1;
+ default:
+ return 0;
+ }
+ }
+ return 0;
+}
+
+static krb5_boolean
+chk_heimdal_seqnum(krb5_ui_4 exp_seq, krb5_ui_4 in_seq)
+{
+ if (( exp_seq & 0xFF800000) == 0x00800000
+ && (in_seq & 0xFF800000) == 0xFF800000
+ && (in_seq & 0x00FFFFFF) == exp_seq)
+ return 1;
+ else if (( exp_seq & 0xFFFF8000) == 0x00008000
+ && (in_seq & 0xFFFF8000) == 0xFFFF8000
+ && (in_seq & 0x0000FFFF) == exp_seq)
+ return 1;
+ else if (( exp_seq & 0xFFFFFF80) == 0x00000080
+ && (in_seq & 0xFFFFFF80) == 0xFFFFFF80
+ && (in_seq & 0x000000FF) == exp_seq)
+ return 1;
+ else
+ return 0;
+}
projects / krb5.git / commitdiff