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sudo/lib/iolog/hostcheck.c

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/*
* Copyright (c) 2020 Laszlo Orban <laszlo.orban@oneidentity.com>
*
* Permission to use, copy, modify, and distribute this software for any
* purpose with or without fee is hereby granted, provided that the above
* copyright notice and this permission notice appear in all copies.
*
* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
*/
/*
* This is an open source non-commercial project. Dear PVS-Studio, please check it.
* PVS-Studio Static Code Analyzer for C, C++ and C#: http://www.viva64.com
*/
#include <config.h>
#if defined(HAVE_OPENSSL)
# if defined(HAVE_WOLFSSL)
# include <wolfssl/options.h>
# endif
# include <sys/types.h>
# include <sys/socket.h>
# include <netinet/in.h>
# include <arpa/inet.h>
# include <stdlib.h>
# include <string.h>
# include <netdb.h>
# define NEED_INET_NTOP /* to expose sudo_inet_ntop in sudo_compat.h */
# include <sudo_compat.h>
# include <sudo_debug.h>
# include <sudo_util.h>
# include <hostcheck.h>
#ifndef INET_ADDRSTRLEN
# define INET_ADDRSTRLEN 16
#endif
#ifndef INET6_ADDRSTRLEN
# define INET6_ADDRSTRLEN 46
#endif
#if !defined(HAVE_ASN1_STRING_GET0_DATA) && !defined(HAVE_WOLFSSL)
# define ASN1_STRING_get0_data(x) ASN1_STRING_data(x)
#endif /* !HAVE_ASN1_STRING_GET0_DATA && !HAVE_WOLFSSL */
/**
* @brief Checks if given hostname resolves to the given IP address.
*
* @param hostname hostname to be resolved
* @param ipaddr ip address to be checked
*
* @return 1 if hostname resolves to the given IP address
* 0 otherwise
*/
static int
forward_lookup_match(const char *hostname, const char *ipaddr)
{
int rc, ret = 0;
struct addrinfo *res = NULL, *p;
void *addr;
struct sockaddr_in *ipv4;
#if defined(HAVE_STRUCT_IN6_ADDR)
struct sockaddr_in6 *ipv6;
char ipstr[INET6_ADDRSTRLEN];
#else
char ipstr[INET_ADDRSTRLEN];
#endif
debug_decl(forward_lookup_match, SUDO_DEBUG_UTIL);
sudo_debug_printf(SUDO_DEBUG_INFO|SUDO_DEBUG_LINENO,
"verify %s resolves to %s", hostname, ipaddr);
if ((rc = getaddrinfo(hostname, NULL, NULL, &res)) != 0) {
sudo_debug_printf(SUDO_DEBUG_ERROR|SUDO_DEBUG_LINENO,
"unable to resolve %s: %s", hostname, gai_strerror(rc));
goto exit;
}
for (p = res; p != NULL; p = p->ai_next) {
if (p->ai_family == AF_INET) {
ipv4 = (struct sockaddr_in *)p->ai_addr;
addr = &(ipv4->sin_addr);
#if defined(HAVE_STRUCT_IN6_ADDR)
} else if (p->ai_family == AF_INET6) {
ipv6 = (struct sockaddr_in6 *)p->ai_addr;
addr = &(ipv6->sin6_addr);
#endif
} else {
goto exit;
}
if (inet_ntop(p->ai_family, addr, ipstr, sizeof(ipstr)) != 0) {
sudo_debug_printf(SUDO_DEBUG_INFO|SUDO_DEBUG_LINENO,
"comparing %s to %s", ipstr, ipaddr);
if (strcmp(ipaddr, ipstr) == 0) {
ret = 1;
break;
}
}
}
exit:
if (res != NULL) {
freeaddrinfo(res);
}
debug_return_int(ret);
}
/**
* @brief Compares the given hostname with a DNS entry in a certificate.
*
* The certificate DNS name can contain wildcards in the left-most label.
* A wildcard can match only one label.
* Accepted names:
* - foo.bar.example.com
* - *.example.com
* - *.bar.example.com
*
* @param hostname peer's name
* @param certname_asn1 hostname in the certificate
*
* @return MatchFound
* MatchNotFound
*/
static HostnameValidationResult
validate_name(const char *hostname, ASN1_STRING *certname_asn1)
{
char *certname_s = (char *)ASN1_STRING_get0_data(certname_asn1);
size_t certname_len = (size_t)ASN1_STRING_length(certname_asn1);
size_t hostname_len = strlen(hostname);
debug_decl(validate_name, SUDO_DEBUG_UTIL);
/* remove last '.' from hostname if exists */
if (hostname_len != 0 && hostname[hostname_len - 1] == '.') {
--hostname_len;
}
sudo_debug_printf(SUDO_DEBUG_INFO|SUDO_DEBUG_LINENO,
"comparing %.*s to %.*s in cert", (int)hostname_len, hostname,
(int)certname_len, certname_s);
/* skip the first label if wildcard */
if (certname_len > 2 && certname_s[0] == '*' && certname_s[1] == '.') {
while (hostname_len != 0) {
--hostname_len;
if (*hostname++ == '.') {
break;
}
}
certname_s += 2;
certname_len -= 2;
}
/* Compare expected hostname with the DNS name */
if (certname_len != hostname_len) {
debug_return_int(MatchNotFound);
}
if (strncasecmp(hostname, certname_s, hostname_len) != 0) {
debug_return_int(MatchNotFound);
}
debug_return_int(MatchFound);
}
/**
* @brief Matches a hostname with the cert's CN.
*
* @param hostname peer's name
* on client side: it is the name where the client is connected to
* on server side, it is in fact an IP address of the remote client
* @param ipaddr peer's IP address
* @param cert peer's X509 certificate
* @param resolve if the value is not 0, the function checks that the value of the CN
* resolves to the given ipaddr or not.
*
* @return MatchFound
* MatchNotFound
* MalformedCertificate
* Error
*/
static HostnameValidationResult
matches_common_name(const char *hostname, const char *ipaddr, const X509 *cert, int resolve)
{
X509_NAME_ENTRY *common_name_entry = NULL;
ASN1_STRING *common_name_asn1 = NULL;
int common_name_loc;
debug_decl(matches_common_name, SUDO_DEBUG_UTIL);
/* Find the position of the CN field in the Subject field of the certificate */
common_name_loc = X509_NAME_get_index_by_NID(X509_get_subject_name((X509 *) cert), NID_commonName, -1);
if (common_name_loc < 0) {
debug_return_int(Error);
}
/* Extract the CN field */
common_name_entry = X509_NAME_get_entry(X509_get_subject_name((X509 *) cert), common_name_loc);
if (common_name_entry == NULL) {
debug_return_int(Error);
}
/* Convert the CN field to a C string */
common_name_asn1 = X509_NAME_ENTRY_get_data(common_name_entry);
if (common_name_asn1 == NULL) {
debug_return_int(Error);
}
const unsigned char *common_name_str = ASN1_STRING_get0_data(common_name_asn1);
const size_t common_name_length = (size_t)ASN1_STRING_length(common_name_asn1);
/* Make sure there isn't an embedded NUL character in the CN */
if (memchr(common_name_str, '\0', common_name_length) != NULL) {
debug_return_int(MalformedCertificate);
}
/* Compare expected hostname with the CN */
if (validate_name(hostname, common_name_asn1) == MatchFound) {
debug_return_int(MatchFound);
}
char *nullterm_common_name = malloc(common_name_length + 1);
if (nullterm_common_name == NULL) {
debug_return_int(Error);
}
memcpy(nullterm_common_name, common_name_str, common_name_length);
nullterm_common_name[common_name_length] = '\0';
/* check if hostname in the CN field resolves to the given ip address */
if (resolve && forward_lookup_match(nullterm_common_name, ipaddr)) {
free(nullterm_common_name);
debug_return_int(MatchFound);
}
free(nullterm_common_name);
debug_return_int(MatchNotFound);
}
/**
* @brief Matches a hostname or ipaddr with the cert's corresponding SAN field.
*
* SAN can have different fields. For hostname matching, the GEN_DNS field is used,
* for IP address matching, the GEN_IPADD field is used.
* Since SAN is an X503 v3 extension, it can happen that the cert does
* not contain SAN at all.
*
* @param hostname remote peer's name
* on client side: it is the name where the client is connected to
* on server side, it is in fact an IP address of the remote client
* @param ipaddr remote peer's IP address
* @param cert peer's X509 certificate
* @param resolve if the value is not 0, the function checks that the value of the
* SAN GEN_DNS resolves to the given ipaddr or not.
*
* @return MatchFound
* MatchNotFound
* NoSANPresent
* MalformedCertificate
* Error
*/
static HostnameValidationResult
matches_subject_alternative_name(const char *hostname, const char *ipaddr, const X509 *cert, int resolve)
{
HostnameValidationResult result = MatchNotFound;
int i;
int san_names_nb;
STACK_OF(GENERAL_NAME) *san_names = NULL;
debug_decl(matches_subject_alternative_name, SUDO_DEBUG_UTIL);
/* Try to extract the names within the SAN extension from the certificate */
san_names = X509_get_ext_d2i((X509 *) cert, NID_subject_alt_name, NULL, NULL);
if (san_names == NULL) {
debug_return_int(NoSANPresent);
}
san_names_nb = sk_GENERAL_NAME_num(san_names);
/* Check each name within the extension */
for (i=0; i<san_names_nb; i++) {
const GENERAL_NAME *current_name = sk_GENERAL_NAME_value(san_names, i);
if (current_name->type == GEN_DNS) {
const unsigned char *dns_name = ASN1_STRING_get0_data(current_name->d.dNSName);
const size_t dns_name_length = (size_t)ASN1_STRING_length(current_name->d.dNSName);
/* Make sure there isn't an embedded NUL character in the DNS name */
if (memchr(dns_name, '\0', dns_name_length) != NULL) {
result = MalformedCertificate;
break;
} else {
/* Compare expected hostname with the DNS name */
if (validate_name(hostname, current_name->d.dNSName) == MatchFound) {
result = MatchFound;
break;
}
char *nullterm_dns_name = malloc(dns_name_length + 1);
if (nullterm_dns_name == NULL) {
debug_return_int(Error);
}
memcpy(nullterm_dns_name, dns_name, dns_name_length);
nullterm_dns_name[dns_name_length] = '\0';
if (resolve && forward_lookup_match(nullterm_dns_name, ipaddr)) {
free(nullterm_dns_name);
result = MatchFound;
break;
}
free(nullterm_dns_name);
}
} else if (current_name->type == GEN_IPADD) {
const unsigned char *san_ip = ASN1_STRING_get0_data(current_name->d.iPAddress);
#if defined(HAVE_STRUCT_IN6_ADDR)
char san_ip_str[INET6_ADDRSTRLEN];
#else
char san_ip_str[INET_ADDRSTRLEN];
#endif
/* IPV4 address */
if(current_name->d.iPAddress->length == 4) {
if (inet_ntop(AF_INET, san_ip, san_ip_str, INET_ADDRSTRLEN) == NULL) {
result = MalformedCertificate;
break;
}
#if defined(HAVE_STRUCT_IN6_ADDR)
/* IPV6 address */
} else if (current_name->d.iPAddress->length == 16) {
if (inet_ntop(AF_INET6, san_ip, san_ip_str, INET6_ADDRSTRLEN) == NULL) {
result = MalformedCertificate;
break;
}
# endif
} else {
result = MalformedCertificate;
break;
}
if (strcasecmp(ipaddr, san_ip_str) == 0) {
result = MatchFound;
break;
}
}
}
sk_GENERAL_NAME_pop_free(san_names, GENERAL_NAME_free);
debug_return_int(result);
}
/**
* @brief Do hostname/IP validation on the given X509 certificate.
*
* According to RFC 6125 section 6.4.4, first the certificate's SAN field
* has to be checked. If there is no SAN field, the certificate's CN field
* has to be checked.
*
* @param cert X509 certificate
* @param hostname remote peer's name
* on client side: it is the name where the client is connected to
* on server side, it is in fact an IP address of the remote client
* @param ipaddr remote peer's IP address
* @param resolve if the value is not 0, the function checks that the value of the
* SAN GEN_DNS or the value of CN resolves to the given ipaddr or not.
*
* @return MatchFound
* MatchNotFound
* MalformedCertificate
* Error
*/
HostnameValidationResult
validate_hostname(const X509 *cert, const char *hostname, const char *ipaddr, int resolve)
{
HostnameValidationResult res = MatchFound;
debug_decl(validate_hostname, SUDO_DEBUG_UTIL);
/* hostname can be also an ip address, if client connects
* to ip instead of FQDN
*/
if((ipaddr == NULL) || (cert == NULL)) {
debug_return_int(Error);
}
/* check SAN first if exists */
res = matches_subject_alternative_name(hostname, ipaddr, cert, resolve);
/* According to RFC 6125 section 6.4.4, check CN only,
* if no SAN name was provided
*/
if (res == NoSANPresent) {
res = matches_common_name(hostname, ipaddr, cert, resolve);
}
debug_return_int(res);
}
#endif /* HAVE_OPENSSL */
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