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From b0372e31b81321a820204450a35c7633caf1b7dd Mon Sep 17 00:00:00 2001
From: Greg Hudson <ghudson@mit.edu>
Date: Fri, 14 Jan 2022 02:05:58 -0500
Subject: [PATCH] Factor out PAC checksum verification
Reduce code repetition in PAC checksum handling by adding a helper
function. Remove the unnecessary prefix on several function names.
---
src/lib/krb5/krb/pac.c | 173 +++++++++++++----------------------------
1 file changed, 55 insertions(+), 118 deletions(-)
diff --git a/src/lib/krb5/krb/pac.c b/src/lib/krb5/krb/pac.c
index 6eb23d8090..2f6ad4e1df 100644
--- a/src/lib/krb5/krb/pac.c
+++ b/src/lib/krb5/krb/pac.c
@@ -493,10 +493,8 @@ k5_pac_validate_client(krb5_context context,
}
static krb5_error_code
-k5_pac_zero_signature(krb5_context context,
- const krb5_pac pac,
- krb5_ui_4 type,
- krb5_data *data)
+zero_signature(krb5_context context, const krb5_pac pac, krb5_ui_4 type,
+ krb5_data *data)
{
PAC_INFO_BUFFER *buffer = NULL;
size_t i;
@@ -530,151 +528,89 @@ k5_pac_zero_signature(krb5_context context,
}
static krb5_error_code
-k5_pac_verify_server_checksum(krb5_context context,
- const krb5_pac pac,
- const krb5_keyblock *server)
+verify_checksum(krb5_context context, const krb5_pac pac, uint32_t buffer_type,
+ const krb5_keyblock *key, krb5_keyusage usage,
+ const krb5_data *data)
{
krb5_error_code ret;
- krb5_data pac_data; /* PAC with zeroed checksums */
+ krb5_data buffer;
+ krb5_cksumtype cksumtype;
krb5_checksum checksum;
- krb5_data checksum_data;
krb5_boolean valid;
- krb5_octet *p;
+ size_t cksumlen;
- ret = k5_pac_locate_buffer(context, pac, KRB5_PAC_SERVER_CHECKSUM,
- &checksum_data);
+ ret = k5_pac_locate_buffer(context, pac, buffer_type, &buffer);
if (ret != 0)
return ret;
-
- if (checksum_data.length < PAC_SIGNATURE_DATA_LENGTH)
+ if (buffer.length < PAC_SIGNATURE_DATA_LENGTH)
return KRB5_BAD_MSIZE;
- p = (krb5_octet *)checksum_data.data;
- checksum.checksum_type = load_32_le(p);
- checksum.length = checksum_data.length - PAC_SIGNATURE_DATA_LENGTH;
- checksum.contents = p + PAC_SIGNATURE_DATA_LENGTH;
- if (checksum.checksum_type == CKSUMTYPE_SHA1)
+ cksumtype = load_32_le(buffer.data);
+ if (buffer_type == KRB5_PAC_SERVER_CHECKSUM && cksumtype == CKSUMTYPE_SHA1)
return KRB5KDC_ERR_SUMTYPE_NOSUPP;
- if (!krb5_c_is_keyed_cksum(checksum.checksum_type))
+ if (!krb5_c_is_keyed_cksum(cksumtype))
return KRB5KRB_ERR_GENERIC;
- pac_data.length = pac->data.length;
- pac_data.data = k5memdup(pac->data.data, pac->data.length, &ret);
- if (pac_data.data == NULL)
- return ret;
-
- /* Zero out both checksum buffers */
- ret = k5_pac_zero_signature(context, pac, KRB5_PAC_SERVER_CHECKSUM,
- &pac_data);
- if (ret != 0) {
- free(pac_data.data);
- return ret;
- }
-
- ret = k5_pac_zero_signature(context, pac, KRB5_PAC_PRIVSVR_CHECKSUM,
- &pac_data);
- if (ret != 0) {
- free(pac_data.data);
+ /* There may be an RODCIdentifier trailer (see [MS-PAC] 2.8), so look up
+ * the length of the checksum by its type. */
+ ret = krb5_c_checksum_length(context, cksumtype, &cksumlen);
+ if (ret)
return ret;
- }
+ if (cksumlen > buffer.length - PAC_SIGNATURE_DATA_LENGTH)
+ return KRB5_BAD_MSIZE;
+ checksum.checksum_type = cksumtype;
+ checksum.length = cksumlen;
+ checksum.contents = (uint8_t *)buffer.data + PAC_SIGNATURE_DATA_LENGTH;
- ret = krb5_c_verify_checksum(context, server,
- KRB5_KEYUSAGE_APP_DATA_CKSUM,
- &pac_data, &checksum, &valid);
+ ret = krb5_c_verify_checksum(context, key, usage, data, &checksum, &valid);
+ return ret ? ret : (valid ? 0 : KRB5KRB_AP_ERR_MODIFIED);
+}
- free(pac_data.data);
+static krb5_error_code
+verify_server_checksum(krb5_context context, const krb5_pac pac,
+ const krb5_keyblock *server)
+{
+ krb5_error_code ret;
+ krb5_data copy; /* PAC with zeroed checksums */
- if (ret != 0) {
+ ret = krb5int_copy_data_contents(context, &pac->data, &copy);
+ if (ret)
return ret;
- }
- if (valid == FALSE)
- ret = KRB5KRB_AP_ERR_MODIFIED;
+ /* Zero out both checksum buffers */
+ ret = zero_signature(context, pac, KRB5_PAC_SERVER_CHECKSUM, &copy);
+ if (ret)
+ goto cleanup;
+ ret = zero_signature(context, pac, KRB5_PAC_PRIVSVR_CHECKSUM, &copy);
+ if (ret)
+ goto cleanup;
+
+ ret = verify_checksum(context, pac, KRB5_PAC_SERVER_CHECKSUM, server,
+ KRB5_KEYUSAGE_APP_DATA_CKSUM, &copy);
+cleanup:
+ free(copy.data);
return ret;
}
static krb5_error_code
-k5_pac_verify_kdc_checksum(krb5_context context,
- const krb5_pac pac,
- const krb5_keyblock *privsvr)
+verify_kdc_checksum(krb5_context context, const krb5_pac pac,
+ const krb5_keyblock *privsvr)
{
krb5_error_code ret;
- krb5_data server_checksum, privsvr_checksum;
- krb5_checksum checksum;
- krb5_boolean valid;
- krb5_octet *p;
-
- ret = k5_pac_locate_buffer(context, pac, KRB5_PAC_PRIVSVR_CHECKSUM,
- &privsvr_checksum);
- if (ret != 0)
- return ret;
-
- if (privsvr_checksum.length < PAC_SIGNATURE_DATA_LENGTH)
- return KRB5_BAD_MSIZE;
+ krb5_data server_checksum;
ret = k5_pac_locate_buffer(context, pac, KRB5_PAC_SERVER_CHECKSUM,
&server_checksum);
- if (ret != 0)
+ if (ret)
return ret;
-
if (server_checksum.length < PAC_SIGNATURE_DATA_LENGTH)
return KRB5_BAD_MSIZE;
-
- p = (krb5_octet *)privsvr_checksum.data;
- checksum.checksum_type = load_32_le(p);
- checksum.length = privsvr_checksum.length - PAC_SIGNATURE_DATA_LENGTH;
- checksum.contents = p + PAC_SIGNATURE_DATA_LENGTH;
- if (!krb5_c_is_keyed_cksum(checksum.checksum_type))
- return KRB5KRB_ERR_GENERIC;
-
server_checksum.data += PAC_SIGNATURE_DATA_LENGTH;
server_checksum.length -= PAC_SIGNATURE_DATA_LENGTH;
- ret = krb5_c_verify_checksum(context, privsvr,
- KRB5_KEYUSAGE_APP_DATA_CKSUM,
- &server_checksum, &checksum, &valid);
- if (ret != 0)
- return ret;
-
- if (valid == FALSE)
- ret = KRB5KRB_AP_ERR_MODIFIED;
-
- return ret;
-}
-
-static krb5_error_code
-verify_ticket_checksum(krb5_context context, const krb5_pac pac,
- const krb5_data *ticket, const krb5_keyblock *privsvr)
-{
- krb5_error_code ret;
- krb5_checksum checksum;
- krb5_data checksum_data;
- krb5_boolean valid;
- krb5_octet *p;
-
- ret = k5_pac_locate_buffer(context, pac, KRB5_PAC_TICKET_CHECKSUM,
- &checksum_data);
- if (ret != 0)
- return KRB5KRB_AP_ERR_MODIFIED;
-
- if (checksum_data.length < PAC_SIGNATURE_DATA_LENGTH)
- return KRB5_BAD_MSIZE;
-
- p = (krb5_octet *)checksum_data.data;
- checksum.checksum_type = load_32_le(p);
- checksum.length = checksum_data.length - PAC_SIGNATURE_DATA_LENGTH;
- checksum.contents = p + PAC_SIGNATURE_DATA_LENGTH;
- if (!krb5_c_is_keyed_cksum(checksum.checksum_type))
- return KRB5KRB_ERR_GENERIC;
-
- ret = krb5_c_verify_checksum(context, privsvr,
- KRB5_KEYUSAGE_APP_DATA_CKSUM, ticket,
- &checksum, &valid);
- if (ret != 0)
- return ret;
-
- return valid ? 0 : KRB5KRB_AP_ERR_MODIFIED;
+ return verify_checksum(context, pac, KRB5_PAC_PRIVSVR_CHECKSUM, privsvr,
+ KRB5_KEYUSAGE_APP_DATA_CKSUM, &server_checksum);
}
/* Per MS-PAC 2.8.3, tickets encrypted to TGS and password change principals
@@ -761,7 +697,8 @@ krb5_kdc_verify_ticket(krb5_context context, const krb5_enc_tkt_part *enc_tkt,
if (ret)
goto cleanup;
- ret = verify_ticket_checksum(context, pac, recoded_tkt, privsvr);
+ ret = verify_checksum(context, pac, KRB5_PAC_TICKET_CHECKSUM, privsvr,
+ KRB5_KEYUSAGE_APP_DATA_CKSUM, recoded_tkt);
if (ret)
goto cleanup;
}
@@ -804,13 +741,13 @@ krb5_pac_verify_ext(krb5_context context,
krb5_error_code ret;
if (server != NULL) {
- ret = k5_pac_verify_server_checksum(context, pac, server);
+ ret = verify_server_checksum(context, pac, server);
if (ret != 0)
return ret;
}
if (privsvr != NULL) {
- ret = k5_pac_verify_kdc_checksum(context, pac, privsvr);
+ ret = verify_kdc_checksum(context, pac, privsvr);
if (ret != 0)
return ret;
}
--
2.39.2
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