Revision f5c7f5dfbaf0d2f7d946d0fe86f08e6bcb36ed0d authored by Matt Caswell on 30 June 2016, 12:17:08 UTC, committed by Matt Caswell on 22 August 2016, 09:53:55 UTC
DTLS can handle out of order record delivery. Additionally since handshake messages can be bigger than will fit into a single packet, the messages can be fragmented across multiple records (as with normal TLS). That means that the messages can arrive mixed up, and we have to reassemble them. We keep a queue of buffered messages that are "from the future", i.e. messages we're not ready to deal with yet but have arrived early. The messages held there may not be full yet - they could be one or more fragments that are still in the process of being reassembled. The code assumes that we will eventually complete the reassembly and when that occurs the complete message is removed from the queue at the point that we need to use it. However, DTLS is also tolerant of packet loss. To get around that DTLS messages can be retransmitted. If we receive a full (non-fragmented) message from the peer after previously having received a fragment of that message, then we ignore the message in the queue and just use the non-fragmented version. At that point the queued message will never get removed. Additionally the peer could send "future" messages that we never get to in order to complete the handshake. Each message has a sequence number (starting from 0). We will accept a message fragment for the current message sequence number, or for any sequence up to 10 into the future. However if the Finished message has a sequence number of 2, anything greater than that in the queue is just left there. So, in those two ways we can end up with "orphaned" data in the queue that will never get removed - except when the connection is closed. At that point all the queues are flushed. An attacker could seek to exploit this by filling up the queues with lots of large messages that are never going to be used in order to attempt a DoS by memory exhaustion. I will assume that we are only concerned with servers here. It does not seem reasonable to be concerned about a memory exhaustion attack on a client. They are unlikely to process enough connections for this to be an issue. A "long" handshake with many messages might be 5 messages long (in the incoming direction), e.g. ClientHello, Certificate, ClientKeyExchange, CertificateVerify, Finished. So this would be message sequence numbers 0 to 4. Additionally we can buffer up to 10 messages in the future. Therefore the maximum number of messages that an attacker could send that could get orphaned would typically be 15. The maximum size that a DTLS message is allowed to be is defined by max_cert_list, which by default is 100k. Therefore the maximum amount of "orphaned" memory per connection is 1500k. Message sequence numbers get reset after the Finished message, so renegotiation will not extend the maximum number of messages that can be orphaned per connection. As noted above, the queues do get cleared when the connection is closed. Therefore in order to mount an effective attack, an attacker would have to open many simultaneous connections. Issue reported by Quan Luo. CVE-2016-2179 Reviewed-by: Richard Levitte <levitte@openssl.org>
1 parent 5dfd038
v3nametest.c
/*
* Copyright 2012-2016 The OpenSSL Project Authors. All Rights Reserved.
*
* Licensed under the OpenSSL license (the "License"). You may not use
* this file except in compliance with the License. You can obtain a copy
* in the file LICENSE in the source distribution or at
* https://www.openssl.org/source/license.html
*/
#include <openssl/x509.h>
#include <openssl/x509v3.h>
#include "../e_os.h"
#include <string.h>
static const char *const names[] = {
"a", "b", ".", "*", "@",
".a", "a.", ".b", "b.", ".*", "*.", "*@", "@*", "a@", "@a", "b@", "..",
"-example.com", "example-.com",
"@@", "**", "*.com", "*com", "*.*.com", "*com", "com*", "*example.com",
"*@example.com", "test@*.example.com", "example.com", "www.example.com",
"test.www.example.com", "*.example.com", "*.www.example.com",
"test.*.example.com", "www.*.com",
".www.example.com", "*www.example.com",
"example.net", "xn--rger-koa.example.com",
"*.xn--rger-koa.example.com", "www.xn--rger-koa.example.com",
"*.good--example.com", "www.good--example.com",
"*.xn--bar.com", "xn--foo.xn--bar.com",
"a.example.com", "b.example.com",
"postmaster@example.com", "Postmaster@example.com",
"postmaster@EXAMPLE.COM",
NULL
};
static const char *const exceptions[] = {
"set CN: host: [*.example.com] matches [a.example.com]",
"set CN: host: [*.example.com] matches [b.example.com]",
"set CN: host: [*.example.com] matches [www.example.com]",
"set CN: host: [*.example.com] matches [xn--rger-koa.example.com]",
"set CN: host: [*.www.example.com] matches [test.www.example.com]",
"set CN: host: [*.www.example.com] matches [.www.example.com]",
"set CN: host: [*www.example.com] matches [www.example.com]",
"set CN: host: [test.www.example.com] matches [.www.example.com]",
"set CN: host: [*.xn--rger-koa.example.com] matches [www.xn--rger-koa.example.com]",
"set CN: host: [*.xn--bar.com] matches [xn--foo.xn--bar.com]",
"set CN: host: [*.good--example.com] matches [www.good--example.com]",
"set CN: host-no-wildcards: [*.www.example.com] matches [.www.example.com]",
"set CN: host-no-wildcards: [test.www.example.com] matches [.www.example.com]",
"set emailAddress: email: [postmaster@example.com] does not match [Postmaster@example.com]",
"set emailAddress: email: [postmaster@EXAMPLE.COM] does not match [Postmaster@example.com]",
"set emailAddress: email: [Postmaster@example.com] does not match [postmaster@example.com]",
"set emailAddress: email: [Postmaster@example.com] does not match [postmaster@EXAMPLE.COM]",
"set dnsName: host: [*.example.com] matches [www.example.com]",
"set dnsName: host: [*.example.com] matches [a.example.com]",
"set dnsName: host: [*.example.com] matches [b.example.com]",
"set dnsName: host: [*.example.com] matches [xn--rger-koa.example.com]",
"set dnsName: host: [*.www.example.com] matches [test.www.example.com]",
"set dnsName: host-no-wildcards: [*.www.example.com] matches [.www.example.com]",
"set dnsName: host-no-wildcards: [test.www.example.com] matches [.www.example.com]",
"set dnsName: host: [*.www.example.com] matches [.www.example.com]",
"set dnsName: host: [*www.example.com] matches [www.example.com]",
"set dnsName: host: [test.www.example.com] matches [.www.example.com]",
"set dnsName: host: [*.xn--rger-koa.example.com] matches [www.xn--rger-koa.example.com]",
"set dnsName: host: [*.xn--bar.com] matches [xn--foo.xn--bar.com]",
"set dnsName: host: [*.good--example.com] matches [www.good--example.com]",
"set rfc822Name: email: [postmaster@example.com] does not match [Postmaster@example.com]",
"set rfc822Name: email: [Postmaster@example.com] does not match [postmaster@example.com]",
"set rfc822Name: email: [Postmaster@example.com] does not match [postmaster@EXAMPLE.COM]",
"set rfc822Name: email: [postmaster@EXAMPLE.COM] does not match [Postmaster@example.com]",
NULL
};
static int is_exception(const char *msg)
{
const char *const *p;
for (p = exceptions; *p; ++p)
if (strcmp(msg, *p) == 0)
return 1;
return 0;
}
static int set_cn(X509 *crt, ...)
{
int ret = 0;
X509_NAME *n = NULL;
va_list ap;
va_start(ap, crt);
n = X509_NAME_new();
if (n == NULL)
goto out;
while (1) {
int nid;
const char *name;
nid = va_arg(ap, int);
if (nid == 0)
break;
name = va_arg(ap, const char *);
if (!X509_NAME_add_entry_by_NID(n, nid, MBSTRING_ASC,
(unsigned char *)name, -1, -1, 1))
goto out;
}
if (!X509_set_subject_name(crt, n))
goto out;
ret = 1;
out:
X509_NAME_free(n);
va_end(ap);
return ret;
}
/*-
int X509_add_ext(X509 *x, X509_EXTENSION *ex, int loc);
X509_EXTENSION *X509_EXTENSION_create_by_NID(X509_EXTENSION **ex,
int nid, int crit, ASN1_OCTET_STRING *data);
int X509_add_ext(X509 *x, X509_EXTENSION *ex, int loc);
*/
static int set_altname(X509 *crt, ...)
{
int ret = 0;
GENERAL_NAMES *gens = NULL;
GENERAL_NAME *gen = NULL;
ASN1_IA5STRING *ia5 = NULL;
va_list ap;
va_start(ap, crt);
gens = sk_GENERAL_NAME_new_null();
if (gens == NULL)
goto out;
while (1) {
int type;
const char *name;
type = va_arg(ap, int);
if (type == 0)
break;
name = va_arg(ap, const char *);
gen = GENERAL_NAME_new();
if (gen == NULL)
goto out;
ia5 = ASN1_IA5STRING_new();
if (ia5 == NULL)
goto out;
if (!ASN1_STRING_set(ia5, name, -1))
goto out;
switch (type) {
case GEN_EMAIL:
case GEN_DNS:
GENERAL_NAME_set0_value(gen, type, ia5);
ia5 = NULL;
break;
default:
abort();
}
sk_GENERAL_NAME_push(gens, gen);
gen = NULL;
}
if (!X509_add1_ext_i2d(crt, NID_subject_alt_name, gens, 0, 0))
goto out;
ret = 1;
out:
ASN1_IA5STRING_free(ia5);
GENERAL_NAME_free(gen);
GENERAL_NAMES_free(gens);
va_end(ap);
return ret;
}
static int set_cn1(X509 *crt, const char *name)
{
return set_cn(crt, NID_commonName, name, 0);
}
static int set_cn_and_email(X509 *crt, const char *name)
{
return set_cn(crt, NID_commonName, name,
NID_pkcs9_emailAddress, "dummy@example.com", 0);
}
static int set_cn2(X509 *crt, const char *name)
{
return set_cn(crt, NID_commonName, "dummy value",
NID_commonName, name, 0);
}
static int set_cn3(X509 *crt, const char *name)
{
return set_cn(crt, NID_commonName, name,
NID_commonName, "dummy value", 0);
}
static int set_email1(X509 *crt, const char *name)
{
return set_cn(crt, NID_pkcs9_emailAddress, name, 0);
}
static int set_email2(X509 *crt, const char *name)
{
return set_cn(crt, NID_pkcs9_emailAddress, "dummy@example.com",
NID_pkcs9_emailAddress, name, 0);
}
static int set_email3(X509 *crt, const char *name)
{
return set_cn(crt, NID_pkcs9_emailAddress, name,
NID_pkcs9_emailAddress, "dummy@example.com", 0);
}
static int set_email_and_cn(X509 *crt, const char *name)
{
return set_cn(crt, NID_pkcs9_emailAddress, name,
NID_commonName, "www.example.org", 0);
}
static int set_altname_dns(X509 *crt, const char *name)
{
return set_altname(crt, GEN_DNS, name, 0);
}
static int set_altname_email(X509 *crt, const char *name)
{
return set_altname(crt, GEN_EMAIL, name, 0);
}
struct set_name_fn {
int (*fn) (X509 *, const char *);
const char *name;
int host;
int email;
};
static const struct set_name_fn name_fns[] = {
{set_cn1, "set CN", 1, 0},
{set_cn2, "set CN", 1, 0},
{set_cn3, "set CN", 1, 0},
{set_cn_and_email, "set CN", 1, 0},
{set_email1, "set emailAddress", 0, 1},
{set_email2, "set emailAddress", 0, 1},
{set_email3, "set emailAddress", 0, 1},
{set_email_and_cn, "set emailAddress", 0, 1},
{set_altname_dns, "set dnsName", 1, 0},
{set_altname_email, "set rfc822Name", 0, 1},
{NULL, NULL, 0}
};
static X509 *make_cert()
{
X509 *ret = NULL;
X509 *crt = NULL;
X509_NAME *issuer = NULL;
crt = X509_new();
if (crt == NULL)
goto out;
if (!X509_set_version(crt, 3))
goto out;
ret = crt;
crt = NULL;
out:
X509_NAME_free(issuer);
return ret;
}
static int errors;
static void check_message(const struct set_name_fn *fn, const char *op,
const char *nameincert, int match, const char *name)
{
char msg[1024];
if (match < 0)
return;
BIO_snprintf(msg, sizeof(msg), "%s: %s: [%s] %s [%s]",
fn->name, op, nameincert,
match ? "matches" : "does not match", name);
if (is_exception(msg))
return;
puts(msg);
++errors;
}
static void run_cert(X509 *crt, const char *nameincert,
const struct set_name_fn *fn)
{
const char *const *pname = names;
while (*pname) {
int samename = strcasecmp(nameincert, *pname) == 0;
size_t namelen = strlen(*pname);
char *name = malloc(namelen);
int match, ret;
memcpy(name, *pname, namelen);
ret = X509_check_host(crt, name, namelen, 0, NULL);
match = -1;
if (ret < 0) {
fprintf(stderr, "internal error in X509_check_host");
++errors;
} else if (fn->host) {
if (ret == 1 && !samename)
match = 1;
if (ret == 0 && samename)
match = 0;
} else if (ret == 1)
match = 1;
check_message(fn, "host", nameincert, match, *pname);
ret = X509_check_host(crt, name, namelen,
X509_CHECK_FLAG_NO_WILDCARDS, NULL);
match = -1;
if (ret < 0) {
fprintf(stderr, "internal error in X509_check_host");
++errors;
} else if (fn->host) {
if (ret == 1 && !samename)
match = 1;
if (ret == 0 && samename)
match = 0;
} else if (ret == 1)
match = 1;
check_message(fn, "host-no-wildcards", nameincert, match, *pname);
ret = X509_check_email(crt, name, namelen, 0);
match = -1;
if (fn->email) {
if (ret && !samename)
match = 1;
if (!ret && samename && strchr(nameincert, '@') != NULL)
match = 0;
} else if (ret)
match = 1;
check_message(fn, "email", nameincert, match, *pname);
++pname;
free(name);
}
}
int main(void)
{
const struct set_name_fn *pfn = name_fns;
while (pfn->name) {
const char *const *pname = names;
while (*pname) {
X509 *crt = make_cert();
if (crt == NULL) {
fprintf(stderr, "make_cert failed\n");
return 1;
}
if (!pfn->fn(crt, *pname)) {
fprintf(stderr, "X509 name setting failed\n");
return 1;
}
run_cert(crt, *pname, pfn);
X509_free(crt);
++pname;
}
++pfn;
}
return errors > 0 ? 1 : 0;
}
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