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Remove support for tls-unique channel binding. 

There are some problems with the tls-unique channel binding type. It's not
supported by all SSL libraries, and strictly speaking it's not defined for
TLS 1.3 at all, even though at least in OpenSSL, the functions used for it
still seem to work with TLS 1.3 connections. And since we had no
mechanism to negotiate what channel binding type to use, there would be
awkward interoperability issues if a server only supported some channel
binding types. tls-server-end-point seems feasible to support with any SSL
library, so let's just stick to that.

This removes the scram_channel_binding libpq option altogether, since there
is now only one supported channel binding type.

This also removes all the channel binding tests from the SSL test suite.
They were really just testing the scram_channel_binding option, which
is now gone. Channel binding is used if both client and server support it,
so it is used in the existing tests. It would be good to have some tests
specifically for channel binding, to make sure it really is used, and the
different combinations of a client and a server that support or doesn't
support it. The current set of settings we have make it hard to write such
tests, but I did test those things manually, by disabling
HAVE_BE_TLS_GET_CERTIFICATE_HASH and/or
HAVE_PGTLS_GET_PEER_CERTIFICATE_HASH.

I also removed the SCRAM_CHANNEL_BINDING_TLS_END_POINT constant. This is a
matter of taste, but IMO it's more readable to just use the
"tls-server-end-point" string.

Refactor the checks on whether the SSL library supports the functions
needed for tls-server-end-point channel binding. Now the server won't
advertise, and the client won't choose, the SCRAM-SHA-256-PLUS variant, if
compiled with an OpenSSL version too old to support it.

In the passing, add some sanity checks to check that the chosen SASL
mechanism, SCRAM-SHA-256 or SCRAM-SHA-256-PLUS, matches whether the SCRAM
exchange used channel binding or not. For example, if the client selects
the non-channel-binding variant SCRAM-SHA-256, but in the SCRAM message
uses channel binding anyway. It's harmless from a security point of view,
I believe, and I'm not sure if there are some other conditions that would
cause the connection to fail, but it seems better to be strict about these
things and check explicitly.

Discussion: https://www.postgresql.org/message-id/ec787074-2305-c6f4-86aa-6902f98485a4%40iki.fi
This commit is contained in:
Heikki Linnakangas 2018-08-05 13:44:21 +03:00
parent 7a46068f47
commit 77291139c7
15 changed files with 245 additions and 335 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

28
doc/src/sgml/libpq.sgml
View File

@ -1245,34 +1245,6 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
</listitem>
</varlistentry>
<varlistentry id="libpq-scram-channel-binding" xreflabel="scram_channel_binding">
<term><literal>scram_channel_binding</literal></term>
<listitem>
<para>
Specifies the channel binding type to use with SCRAM
authentication. While <acronym>SCRAM</acronym> alone prevents
the replay of transmitted hashed passwords, channel binding also
prevents man-in-the-middle attacks.
</para>
<para>
The list of channel binding types supported by the server are
listed in <xref linkend="sasl-authentication"/>. An empty value
specifies that the client will not use channel binding. If this
parameter is not specified, <literal>tls-unique</literal> is used,
if supported by both server and client.
Channel binding is only supported on SSL connections. If the
connection is not using SSL, then this setting is ignored.
</para>
<para>
This parameter is mainly intended for protocol testing. In normal
use, there should not be a need to choose a channel binding type other
than the default one.
</para>
</listitem>
</varlistentry>
<varlistentry id="libpq-connect-replication" xreflabel="replication">
<term><literal>replication</literal></term>
<listitem>

26
doc/src/sgml/protocol.sgml
View File

@ -1576,12 +1576,8 @@ the password is in.
<para>
<firstterm>Channel binding</firstterm> is supported in PostgreSQL builds with
SSL support. The SASL mechanism name for SCRAM with channel binding is
<literal>SCRAM-SHA-256-PLUS</literal>. Two channel binding types are
supported: <literal>tls-unique</literal> and
<literal>tls-server-end-point</literal>, both defined in RFC 5929. Clients
should use <literal>tls-unique</literal> if they can support it.
<literal>tls-server-end-point</literal> is intended for third-party clients
that cannot support <literal>tls-unique</literal> for some reason.
<literal>SCRAM-SHA-256-PLUS</literal>. The channel binding type used by
PostgreSQL is <literal>tls-server-end-point</literal>.
</para>
<para>
@ -1596,19 +1592,11 @@ that cannot support <literal>tls-unique</literal> for some reason.
<para>
<acronym>SCRAM</acronym> with channel binding prevents such
man-in-the-middle attacks by mixing a value into the transmitted
password hash that cannot be retransmitted by a fake server.
In <acronym>SCRAM</acronym> with <literal>tls-unique</literal>
channel binding, the shared secret negotiated during the SSL session
is mixed into the user-supplied password hash. The shared secret
is partly chosen by the server, but not directly transmitted, making
it impossible for a fake server to create an SSL connection with the
client that has the same shared secret it has with the real server.
<acronym>SCRAM</acronym> with <literal>tls-server-end-point</literal>
mixes a hash of the server's certificate into the user-supplied password
hash. While a fake server can retransmit the real server's certificate,
it doesn't have access to the private key matching that certificate, and
therefore cannot prove it is the owner, causing SSL connection failure.
man-in-the-middle attacks by mixing the signature of the server's
certificate into the transmitted password hash. While a fake server can
retransmit the real server's certificate, it doesn't have access to the
private key matching that certificate, and therefore cannot prove it is
the owner, causing SSL connection failure.
</para>
<procedure>

5
doc/src/sgml/release-11.sgml
View File

@ -2693,10 +2693,7 @@ same commits as above
the feature currently does not prevent man-in-the-middle
attacks when using libpq and interfaces built using it. It is
expected that future versions of libpq and interfaces not built
using libpq, e.g. JDBC, will allow this capability. The libpq
options to control the optional channel binding type are <link
linkend="libpq-scram-channel-binding"><option>scram_channel_binding=tls-unique</option></link>
and <option>scram_channel_binding=tls-server-end-point</option>.
using libpq, e.g. JDBC, will allow this capability.
</para>
</listitem>

221
src/backend/libpq/auth-scram.c
View File

@ -17,6 +17,19 @@
* by the SASLprep profile, we skip the SASLprep pre-processing and use
* the raw bytes in calculating the hash.
*
* - If channel binding is used, the channel binding type is always
* "tls-server-end-point". The spec says the default is "tls-unique"
* (RFC 5802, section 6.1. Default Channel Binding), but there are some
* problems with that. Firstly, not all SSL libraries provide an API to
* get the TLS Finished message, required to use "tls-unique". Secondly,
* "tls-unique" is not specified for TLS v1.3, and as of this writing,
* it's not clear if there will be a replacement. We could support both
* "tls-server-end-point" and "tls-unique", but for our use case,
* "tls-unique" doesn't really have any advantages. The main advantage
* of "tls-unique" would be that it works even if the server doesn't
* have a certificate, but PostgreSQL requires a server certificate
* whenever SSL is used, anyway.
*
*
* The password stored in pg_authid consists of the iteration count, salt,
* StoredKey and ServerKey.
@ -111,8 +124,7 @@ typedef struct
const char *username; /* username from startup packet */
Port *port;
char cbind_flag;
char *channel_binding_type;
bool channel_binding_in_use;
int iterations;
char *salt; /* base64-encoded */
@ -120,6 +132,7 @@ typedef struct
uint8 ServerKey[SCRAM_KEY_LEN];
/* Fields of the first message from client */
char cbind_flag;
char *client_first_message_bare;
char *client_username;
char *client_nonce;
@ -155,8 +168,38 @@ static void mock_scram_verifier(const char *username, int *iterations,
char **salt, uint8 *stored_key, uint8 *server_key);
static bool is_scram_printable(char *p);
static char *sanitize_char(char c);
static char *sanitize_str(const char *s);
static char *scram_mock_salt(const char *username);
/*
* pg_be_scram_get_mechanisms
*
* Get a list of SASL mechanisms that this module supports.
*
* For the convenience of building the FE/BE packet that lists the
* mechanisms, the names are appended to the given StringInfo buffer,
* separated by '\0' bytes.
*/
void
pg_be_scram_get_mechanisms(Port *port, StringInfo buf)
{
/*
* Advertise the mechanisms in decreasing order of importance. So the
* channel-binding variants go first, if they are supported. Channel
* binding is only supported with SSL, and only if the SSL implementation
* has a function to get the certificate's hash.
*/
#ifdef HAVE_BE_TLS_GET_CERTIFICATE_HASH
if (port->ssl_in_use)
{
appendStringInfoString(buf, SCRAM_SHA_256_PLUS_NAME);
appendStringInfoChar(buf, '\0');
}
#endif
appendStringInfoString(buf, SCRAM_SHA_256_NAME);
appendStringInfoChar(buf, '\0');
}
/*
* pg_be_scram_init
*
@ -164,13 +207,19 @@ static char *scram_mock_salt(const char *username);
* needs to be called before doing any exchange. It will be filled later
* after the beginning of the exchange with verifier data.
*
* 'username' is the username provided by the client in the startup message.
* 'selected_mech' identifies the SASL mechanism that the client selected.
* It should be one of the mechanisms that we support, as returned by
* pg_be_scram_get_mechanisms().
*
* 'shadow_pass' is the role's password verifier, from pg_authid.rolpassword.
* If 'shadow_pass' is NULL, we still perform an authentication exchange, but
* it will fail, as if an incorrect password was given.
* The username was provided by the client in the startup message, and is
* available in port->user_name. If 'shadow_pass' is NULL, we still perform
* an authentication exchange, but it will fail, as if an incorrect password
* was given.
*/
void *
pg_be_scram_init(Port *port,
const char *selected_mech,
const char *shadow_pass)
{
scram_state *state;
@ -179,7 +228,27 @@ pg_be_scram_init(Port *port,
state = (scram_state *) palloc0(sizeof(scram_state));
state->port = port;
state->state = SCRAM_AUTH_INIT;
state->channel_binding_type = NULL;
/*
* Parse the selected mechanism.
*
* Note that if we don't support channel binding, either because the SSL
* implementation doesn't support it or we're not using SSL at all, we
* would not have advertised the PLUS variant in the first place. If the
* client nevertheless tries to select it, it's a protocol violation like
* selecting any other SASL mechanism we don't support.
*/
#ifdef HAVE_BE_TLS_GET_CERTIFICATE_HASH
if (strcmp(selected_mech, SCRAM_SHA_256_PLUS_NAME) == 0 && port->ssl_in_use)
state->channel_binding_in_use = true;
else
#endif
if (strcmp(selected_mech, SCRAM_SHA_256_NAME) == 0)
state->channel_binding_in_use = false;
else
ereport(ERROR,
(errcode(ERRCODE_PROTOCOL_VIOLATION),
errmsg("client selected an invalid SASL authentication mechanism")));
/*
* Parse the stored password verifier.
@ -655,6 +724,36 @@ sanitize_char(char c)
return buf;
}
/*
* Convert an arbitrary string to printable form, for error messages.
*
* Anything that's not a printable ASCII character is replaced with
* '?', and the string is truncated at 30 characters.
*
* The returned pointer points to a static buffer.
*/
static char *
sanitize_str(const char *s)
{
static char buf[30 + 1];
int i;
for (i = 0; i < sizeof(buf) - 1; i++)
{
char c = s[i];
if (c == '\0')
break;
if (c >= 0x21 && c <= 0x7E)
buf[i] = c;
else
buf[i] = '?';
}
buf[i] = '\0';
return buf;
}
/*
* Read the next attribute and value in a SCRAM exchange message.
*
@ -715,6 +814,8 @@ read_any_attr(char **input, char *attr_p)
static void
read_client_first_message(scram_state *state, char *input)
{
char *channel_binding_type;
input = pstrdup(input);
/*------
@ -790,6 +891,12 @@ read_client_first_message(scram_state *state, char *input)
* The client does not support channel binding or has simply
* decided to not use it. In that case just let it go.
*/
if (state->channel_binding_in_use)
ereport(ERROR,
(errcode(ERRCODE_PROTOCOL_VIOLATION),
errmsg("malformed SCRAM message"),
errdetail("The client selected SCRAM-SHA-256-PLUS, but the SCRAM message does not include channel binding data.")));
input++;
if (*input != ',')
ereport(ERROR,
@ -804,15 +911,22 @@ read_client_first_message(scram_state *state, char *input)
/*
* The client supports channel binding and thinks that the server
* does not. In this case, the server must fail authentication if
* it supports channel binding, which in this implementation is
* the case if a connection is using SSL.
* it supports channel binding.
*/
if (state->channel_binding_in_use)
ereport(ERROR,
(errcode(ERRCODE_PROTOCOL_VIOLATION),
errmsg("malformed SCRAM message"),
errdetail("The client selected SCRAM-SHA-256-PLUS, but the SCRAM message does not include channel binding data.")));
#ifdef HAVE_BE_TLS_GET_CERTIFICATE_HASH
if (state->port->ssl_in_use)
ereport(ERROR,
(errcode(ERRCODE_INVALID_AUTHORIZATION_SPECIFICATION),
errmsg("SCRAM channel binding negotiation error"),
errdetail("The client supports SCRAM channel binding but thinks the server does not. "
"However, this server does support channel binding.")));
#endif
input++;
if (*input != ',')
ereport(ERROR,
@ -826,44 +940,25 @@ read_client_first_message(scram_state *state, char *input)
/*
* The client requires channel binding. Channel binding type
* follows, e.g., "p=tls-unique".
* follows, e.g., "p=tls-server-end-point".
*/
{
char *channel_binding_type;
if (!state->channel_binding_in_use)
ereport(ERROR,
(errcode(ERRCODE_PROTOCOL_VIOLATION),
errmsg("malformed SCRAM message"),
errdetail("The client selected SCRAM-SHA-256 without channel binding, but the SCRAM message includes channel binding data.")));
if (!state->port->ssl_in_use)
{
/*
* Without SSL, we don't support channel binding.
*
* RFC 5802 specifies a particular error code,
* e=server-does-support-channel-binding, for this. But
* it can only be sent in the server-final message, and we
* don't want to go through the motions of the
* authentication, knowing it will fail, just to send that
* error message.
*/
ereport(ERROR,
(errcode(ERRCODE_PROTOCOL_VIOLATION),
errmsg("client requires SCRAM channel binding, but it is not supported")));
}
channel_binding_type = read_attr_value(&input, 'p');
/*
* Read value provided by client. (It is not safe to print
* the name of an unsupported binding type in the error
* message. Pranksters could print arbitrary strings into the
* log that way.)
*/
channel_binding_type = read_attr_value(&input, 'p');
if (strcmp(channel_binding_type, SCRAM_CHANNEL_BINDING_TLS_UNIQUE) != 0 &&
strcmp(channel_binding_type, SCRAM_CHANNEL_BINDING_TLS_END_POINT) != 0)
ereport(ERROR,
(errcode(ERRCODE_PROTOCOL_VIOLATION),
(errmsg("unsupported SCRAM channel-binding type"))));
/* Save the name for handling of subsequent messages */
state->channel_binding_type = pstrdup(channel_binding_type);
}
/*
* The only channel binding type we support is
* tls-server-end-point.
*/
if (strcmp(channel_binding_type, "tls-server-end-point") != 0)
ereport(ERROR,
(errcode(ERRCODE_PROTOCOL_VIOLATION),
(errmsg("unsupported SCRAM channel-binding type \"%s\"",
sanitize_str(channel_binding_type)))));
break;
default:
ereport(ERROR,
@ -1096,8 +1191,9 @@ read_client_final_message(scram_state *state, char *input)
* then followed by the actual binding data depending on the type.
*/
channel_binding = read_attr_value(&p, 'c');
if (state->channel_binding_type)
if (state->channel_binding_in_use)
{
#ifdef HAVE_BE_TLS_GET_CERTIFICATE_HASH
const char *cbind_data = NULL;
size_t cbind_data_len = 0;
size_t cbind_header_len;
@ -1108,39 +1204,18 @@ read_client_final_message(scram_state *state, char *input)
Assert(state->cbind_flag == 'p');
/*
* Fetch data appropriate for channel binding type
*/
if (strcmp(state->channel_binding_type, SCRAM_CHANNEL_BINDING_TLS_UNIQUE) == 0)
{
#ifdef USE_SSL
cbind_data = be_tls_get_peer_finished(state->port, &cbind_data_len);
#endif
}
else if (strcmp(state->channel_binding_type,
SCRAM_CHANNEL_BINDING_TLS_END_POINT) == 0)
{
/* Fetch hash data of server's SSL certificate */
#ifdef USE_SSL
cbind_data = be_tls_get_certificate_hash(state->port,
&cbind_data_len);
#endif
}
else
{
/* should not happen */
elog(ERROR, "invalid channel binding type");
}
/* Fetch hash data of server's SSL certificate */
cbind_data = be_tls_get_certificate_hash(state->port,
&cbind_data_len);
/* should not happen */
if (cbind_data == NULL || cbind_data_len == 0)
elog(ERROR, "empty channel binding data for channel binding type \"%s\"",
state->channel_binding_type);
elog(ERROR, "could not get server certificate hash");
cbind_header_len = 4 + strlen(state->channel_binding_type); /* p=type,, */
cbind_header_len = strlen("p=tls-server-end-point,,"); /* p=type,, */
cbind_input_len = cbind_header_len + cbind_data_len;
cbind_input = palloc(cbind_input_len);
snprintf(cbind_input, cbind_input_len, "p=%s,,", state->channel_binding_type);
snprintf(cbind_input, cbind_input_len, "p=tls-server-end-point,,");
memcpy(cbind_input + cbind_header_len, cbind_data, cbind_data_len);
b64_message = palloc(pg_b64_enc_len(cbind_input_len) + 1);
@ -1156,6 +1231,10 @@ read_client_final_message(scram_state *state, char *input)
ereport(ERROR,
(errcode(ERRCODE_INVALID_AUTHORIZATION_SPECIFICATION),
(errmsg("SCRAM channel binding check failed"))));
#else
/* shouldn't happen, because we checked this earlier already */
elog(ERROR, "channel binding not supported by this build");
#endif
}
else
{

62
src/backend/libpq/auth.c
View File

@ -862,8 +862,7 @@ CheckMD5Auth(Port *port, char *shadow_pass, char **logdetail)
static int
CheckSCRAMAuth(Port *port, char *shadow_pass, char **logdetail)
{
char *sasl_mechs;
char *p;
StringInfoData sasl_mechs;
int mtype;
StringInfoData buf;
void *scram_opaq;
@ -889,42 +888,16 @@ CheckSCRAMAuth(Port *port, char *shadow_pass, char **logdetail)
/*
* Send the SASL authentication request to user. It includes the list of
* authentication mechanisms that are supported. The order of mechanisms
* is advertised in decreasing order of importance. So the
* channel-binding variants go first, if they are supported. Channel
* binding is only supported in SSL builds.
* authentication mechanisms that are supported.
*/
sasl_mechs = palloc(strlen(SCRAM_SHA_256_PLUS_NAME) +
strlen(SCRAM_SHA_256_NAME) + 3);
p = sasl_mechs;
if (port->ssl_in_use)
{
strcpy(p, SCRAM_SHA_256_PLUS_NAME);
p += strlen(SCRAM_SHA_256_PLUS_NAME) + 1;
}
strcpy(p, SCRAM_SHA_256_NAME);
p += strlen(SCRAM_SHA_256_NAME) + 1;
initStringInfo(&sasl_mechs);
pg_be_scram_get_mechanisms(port, &sasl_mechs);
/* Put another '\0' to mark that list is finished. */
p[0] = '\0';
appendStringInfoChar(&sasl_mechs, '\0');
sendAuthRequest(port, AUTH_REQ_SASL, sasl_mechs, p - sasl_mechs + 1);
pfree(sasl_mechs);
/*
* Initialize the status tracker for message exchanges.
*
* If the user doesn't exist, or doesn't have a valid password, or it's
* expired, we still go through the motions of SASL authentication, but
* tell the authentication method that the authentication is "doomed".
* That is, it's going to fail, no matter what.
*
* This is because we don't want to reveal to an attacker what usernames
* are valid, nor which users have a valid password.
*/
scram_opaq = pg_be_scram_init(port, shadow_pass);
sendAuthRequest(port, AUTH_REQ_SASL, sasl_mechs.data, sasl_mechs.len);
pfree(sasl_mechs.data);
/*
* Loop through SASL message exchange. This exchange can consist of
@ -973,13 +946,20 @@ CheckSCRAMAuth(Port *port, char *shadow_pass, char **logdetail)
const char *selected_mech;
selected_mech = pq_getmsgrawstring(&buf);
if (strcmp(selected_mech, SCRAM_SHA_256_NAME) != 0 &&
strcmp(selected_mech, SCRAM_SHA_256_PLUS_NAME) != 0)
{
ereport(ERROR,
(errcode(ERRCODE_PROTOCOL_VIOLATION),
errmsg("client selected an invalid SASL authentication mechanism")));
}
/*
* Initialize the status tracker for message exchanges.
*
* If the user doesn't exist, or doesn't have a valid password, or
* it's expired, we still go through the motions of SASL
* authentication, but tell the authentication method that the
* authentication is "doomed". That is, it's going to fail, no
* matter what.
*
* This is because we don't want to reveal to an attacker what
* usernames are valid, nor which users have a valid password.
*/
scram_opaq = pg_be_scram_init(port, selected_mech, shadow_pass);
inputlen = pq_getmsgint(&buf, 4);
if (inputlen == -1)

27
src/backend/libpq/be-secure-openssl.c
View File

@ -1105,28 +1105,10 @@ be_tls_get_peerdn_name(Port *port, char *ptr, size_t len)
ptr[0] = '\0';
}
char *
be_tls_get_peer_finished(Port *port, size_t *len)
{
char dummy[1];
char *result;
/*
* OpenSSL does not offer an API to directly get the length of the
* expected TLS Finished message, so just do a dummy call to grab this
* information to allow caller to do an allocation with a correct size.
*/
*len = SSL_get_peer_finished(port->ssl, dummy, sizeof(dummy));
result = palloc(*len);
(void) SSL_get_peer_finished(port->ssl, result, *len);
return result;
}
#ifdef HAVE_X509_GET_SIGNATURE_NID
char *
be_tls_get_certificate_hash(Port *port, size_t *len)
{
#ifdef HAVE_X509_GET_SIGNATURE_NID
X509 *server_cert;
char *cert_hash;
const EVP_MD *algo_type = NULL;
@ -1176,13 +1158,8 @@ be_tls_get_certificate_hash(Port *port, size_t *len)
*len = hash_size;
return cert_hash;
#else
ereport(ERROR,
(errcode(ERRCODE_PROTOCOL_VIOLATION),
errmsg("channel binding type \"tls-server-end-point\" is not supported by this build")));
return NULL;
#endif
}
#endif
/*
* Convert an X509 subject name to a cstring.

4
src/include/common/scram-common.h
View File

@ -19,10 +19,6 @@
#define SCRAM_SHA_256_NAME "SCRAM-SHA-256"
#define SCRAM_SHA_256_PLUS_NAME "SCRAM-SHA-256-PLUS" /* with channel binding */
/* Channel binding types */
#define SCRAM_CHANNEL_BINDING_TLS_UNIQUE "tls-unique"
#define SCRAM_CHANNEL_BINDING_TLS_END_POINT "tls-server-end-point"
/* Length of SCRAM keys (client and server) */
#define SCRAM_KEY_LEN PG_SHA256_DIGEST_LENGTH

15
src/include/libpq/libpq-be.h
View File

@ -260,24 +260,23 @@ extern const char *be_tls_get_version(Port *port);
extern const char *be_tls_get_cipher(Port *port);
extern void be_tls_get_peerdn_name(Port *port, char *ptr, size_t len);
/*
* Get the expected TLS Finished message information from the client, useful
* for authorization when doing channel binding.
*
* Result is a palloc'd copy of the TLS Finished message with its size.
*/
extern char *be_tls_get_peer_finished(Port *port, size_t *len);
/*
* Get the server certificate hash for SCRAM channel binding type
* tls-server-end-point.
*
* The result is a palloc'd hash of the server certificate with its
* size, and NULL if there is no certificate available.
*
* This is not supported with old versions of OpenSSL that don't have
* the X509_get_signature_nid() function.
*/
#if defined(USE_OPENSSL) && defined(HAVE_X509_GET_SIGNATURE_NID)
#define HAVE_BE_TLS_GET_CERTIFICATE_HASH
extern char *be_tls_get_certificate_hash(Port *port, size_t *len);
#endif
#endif /* USE_SSL */
extern ProtocolVersion FrontendProtocol;
/* TCP keepalives configuration. These are no-ops on an AF_UNIX socket. */

4
src/include/libpq/scram.h
View File

@ -13,6 +13,7 @@
#ifndef PG_SCRAM_H
#define PG_SCRAM_H
#include "lib/stringinfo.h"
#include "libpq/libpq-be.h"
/* Status codes for message exchange */
@ -21,7 +22,8 @@
#define SASL_EXCHANGE_FAILURE 2
/* Routines dedicated to authentication */
extern void *pg_be_scram_init(Port *port, const char *shadow_pass);
extern void pg_be_scram_get_mechanisms(Port *port, StringInfo buf);
extern void *pg_be_scram_init(Port *port, const char *selected_mech, const char *shadow_pass);
extern int pg_be_scram_exchange(void *opaq, char *input, int inputlen,
char **output, int *outputlen, char **logdetail);

79
src/interfaces/libpq/fe-auth-scram.c
View File

@ -352,17 +352,9 @@ build_client_first_message(fe_scram_state *state)
if (strcmp(state->sasl_mechanism, SCRAM_SHA_256_PLUS_NAME) == 0)
{
Assert(conn->ssl_in_use);
appendPQExpBuffer(&buf, "p=%s", conn->scram_channel_binding);
}
else if (conn->scram_channel_binding == NULL ||
strlen(conn->scram_channel_binding) == 0)
{
/*
* Client has chosen to not show to server that it supports channel
* binding.
*/
appendPQExpBuffer(&buf, "n");
appendPQExpBuffer(&buf, "p=tls-server-end-point");
}
#ifdef HAVE_PGTLS_GET_PEER_CERTIFICATE_HASH
else if (conn->ssl_in_use)
{
/*
@ -370,6 +362,7 @@ build_client_first_message(fe_scram_state *state)
*/
appendPQExpBuffer(&buf, "y");
}
#endif
else
{
/*
@ -432,60 +425,28 @@ build_client_final_message(fe_scram_state *state)
*/
if (strcmp(state->sasl_mechanism, SCRAM_SHA_256_PLUS_NAME) == 0)
{
#ifdef HAVE_PGTLS_GET_PEER_CERTIFICATE_HASH
char *cbind_data = NULL;
size_t cbind_data_len = 0;
size_t cbind_header_len;
char *cbind_input;
size_t cbind_input_len;
if (strcmp(conn->scram_channel_binding, SCRAM_CHANNEL_BINDING_TLS_UNIQUE) == 0)
/* Fetch hash data of server's SSL certificate */
cbind_data =
pgtls_get_peer_certificate_hash(state->conn,
&cbind_data_len);
if (cbind_data == NULL)
{
#ifdef USE_SSL
cbind_data = pgtls_get_finished(state->conn, &cbind_data_len);
if (cbind_data == NULL)
goto oom_error;
#endif
}
else if (strcmp(conn->scram_channel_binding,
SCRAM_CHANNEL_BINDING_TLS_END_POINT) == 0)
{
/* Fetch hash data of server's SSL certificate */
#ifdef USE_SSL
cbind_data =
pgtls_get_peer_certificate_hash(state->conn,
&cbind_data_len);
if (cbind_data == NULL)
{
/* error message is already set on error */
return NULL;
}
#endif
}
else
{
/* should not happen */
/* error message is already set on error */
termPQExpBuffer(&buf);
printfPQExpBuffer(&conn->errorMessage,
libpq_gettext("invalid channel binding type\n"));
return NULL;
}
/* should not happen */
if (cbind_data == NULL || cbind_data_len == 0)
{
if (cbind_data != NULL)
free(cbind_data);
termPQExpBuffer(&buf);
printfPQExpBuffer(&conn->errorMessage,
libpq_gettext("empty channel binding data for channel binding type \"%s\"\n"),
conn->scram_channel_binding);
return NULL;
}
appendPQExpBuffer(&buf, "c=");
/* p=type,, */
cbind_header_len = 4 + strlen(conn->scram_channel_binding);
cbind_header_len = strlen("p=tls-server-end-point,,");
cbind_input_len = cbind_header_len + cbind_data_len;
cbind_input = malloc(cbind_input_len);
if (!cbind_input)
@ -493,8 +454,7 @@ build_client_final_message(fe_scram_state *state)
free(cbind_data);
goto oom_error;
}
snprintf(cbind_input, cbind_input_len, "p=%s,,",
conn->scram_channel_binding);
memcpy(cbind_input, "p=tls-server-end-point,,", cbind_header_len);
memcpy(cbind_input + cbind_header_len, cbind_data, cbind_data_len);
if (!enlargePQExpBuffer(&buf, pg_b64_enc_len(cbind_input_len)))
@ -508,12 +468,21 @@ build_client_final_message(fe_scram_state *state)
free(cbind_data);
free(cbind_input);
#else
/*
* Chose channel binding, but the SSL library doesn't support it.
* Shouldn't happen.
*/
termPQExpBuffer(&buf);
printfPQExpBuffer(&conn->errorMessage,
"channel binding not supported by this build\n");
return NULL;
#endif /* HAVE_PGTLS_GET_PEER_CERTIFICATE_HASH */
}
else if (conn->scram_channel_binding == NULL ||
strlen(conn->scram_channel_binding) == 0)
appendPQExpBuffer(&buf, "c=biws"); /* base64 of "n,," */
#ifdef HAVE_PGTLS_GET_PEER_CERTIFICATE_HASH
else if (conn->ssl_in_use)
appendPQExpBuffer(&buf, "c=eSws"); /* base64 of "y,," */
#endif
else
appendPQExpBuffer(&buf, "c=biws"); /* base64 of "n,," */

25
src/interfaces/libpq/fe-auth.c
View File

@ -530,11 +530,26 @@ pg_SASL_init(PGconn *conn, int payloadlen)
* nothing else has already been picked. If we add more mechanisms, a
* more refined priority mechanism might become necessary.
*/
if (conn->ssl_in_use &&
conn->scram_channel_binding &&
strlen(conn->scram_channel_binding) > 0 &&
strcmp(mechanism_buf.data, SCRAM_SHA_256_PLUS_NAME) == 0)
selected_mechanism = SCRAM_SHA_256_PLUS_NAME;
if (strcmp(mechanism_buf.data, SCRAM_SHA_256_PLUS_NAME) == 0)
{
if (conn->ssl_in_use)
selected_mechanism = SCRAM_SHA_256_PLUS_NAME;
else
{
/*
* The server offered SCRAM-SHA-256-PLUS, but the connection
* is not SSL-encrypted. That's not sane. Perhaps SSL was
* stripped by a proxy? There's no point in continuing,
* because the server will reject the connection anyway if we
* try authenticate without channel binding even though both
* the client and server supported it. The SCRAM exchange
* checks for that, to prevent downgrade attacks.
*/
printfPQExpBuffer(&conn->errorMessage,
libpq_gettext("server offered SCRAM-SHA-256-PLUS authentication over a non-SSL connection\n"));
goto error;
}
}
else if (strcmp(mechanism_buf.data, SCRAM_SHA_256_NAME) == 0 &&
!selected_mechanism)
selected_mechanism = SCRAM_SHA_256_NAME;

8
src/interfaces/libpq/fe-connect.c
View File

@ -123,7 +123,6 @@ static int ldapServiceLookup(const char *purl, PQconninfoOption *options,
#define DefaultOption ""
#define DefaultAuthtype ""
#define DefaultTargetSessionAttrs "any"
#define DefaultSCRAMChannelBinding SCRAM_CHANNEL_BINDING_TLS_UNIQUE
#ifdef USE_SSL
#define DefaultSSLMode "prefer"
#else
@ -264,11 +263,6 @@ static const internalPQconninfoOption PQconninfoOptions[] = {
"TCP-Keepalives-Count", "", 10, /* strlen(INT32_MAX) == 10 */
offsetof(struct pg_conn, keepalives_count)},
{"scram_channel_binding", NULL, DefaultSCRAMChannelBinding, NULL,
"SCRAM-Channel-Binding", "D",
21, /* sizeof("tls-server-end-point") == 21 */
offsetof(struct pg_conn, scram_channel_binding)},
/*
* ssl options are allowed even without client SSL support because the
* client can still handle SSL modes "disable" and "allow". Other
@ -3481,8 +3475,6 @@ freePGconn(PGconn *conn)
free(conn->keepalives_interval);
if (conn->keepalives_count)
free(conn->keepalives_count);
if (conn->scram_channel_binding)
free(conn->scram_channel_binding);
if (conn->sslmode)
free(conn->sslmode);
if (conn->sslcert)

28
src/interfaces/libpq/fe-secure-openssl.c
View File

@ -369,30 +369,10 @@ pgtls_write(PGconn *conn, const void *ptr, size_t len)
return n;
}
char *
pgtls_get_finished(PGconn *conn, size_t *len)
{
char dummy[1];
char *result;
/*
* OpenSSL does not offer an API to get directly the length of the TLS
* Finished message sent, so first do a dummy call to grab this
* information and then do an allocation with the correct size.
*/
*len = SSL_get_finished(conn->ssl, dummy, sizeof(dummy));
result = malloc(*len);
if (result == NULL)
return NULL;
(void) SSL_get_finished(conn->ssl, result, *len);
return result;
}
#ifdef HAVE_X509_GET_SIGNATURE_NID
char *
pgtls_get_peer_certificate_hash(PGconn *conn, size_t *len)
{
#ifdef HAVE_X509_GET_SIGNATURE_NID
X509 *peer_cert;
const EVP_MD *algo_type;
unsigned char hash[EVP_MAX_MD_SIZE]; /* size for SHA-512 */
@ -462,12 +442,8 @@ pgtls_get_peer_certificate_hash(PGconn *conn, size_t *len)
*len = hash_size;
return cert_hash;
#else
printfPQExpBuffer(&conn->errorMessage,
libpq_gettext("channel binding type \"tls-server-end-point\" is not supported by this build\n"));
return NULL;
#endif
}
#endif /* HAVE_X509_GET_SIGNATURE_NID */
/* ------------------------------------------------------------ */
/* OpenSSL specific code */

15
src/interfaces/libpq/libpq-int.h
View File

@ -349,7 +349,6 @@ struct pg_conn
* retransmits */
char *keepalives_count; /* maximum number of TCP keepalive
* retransmits */
char *scram_channel_binding; /* SCRAM channel binding type */
char *sslmode; /* SSL mode (require,prefer,allow,disable) */
char *sslcompression; /* SSL compression (0 or 1) */
char *sslkey; /* client key filename */
@ -715,22 +714,20 @@ extern bool pgtls_read_pending(PGconn *conn);
*/
extern ssize_t pgtls_write(PGconn *conn, const void *ptr, size_t len);
/*
* Get the TLS finish message sent during last handshake.
*
* This information is useful for callers doing channel binding during
* authentication.
*/
extern char *pgtls_get_finished(PGconn *conn, size_t *len);
/*
* Get the hash of the server certificate, for SCRAM channel binding type
* tls-server-end-point.
*
* NULL is sent back to the caller in the event of an error, with an
* error message for the caller to consume.
*
* This is not supported with old versions of OpenSSL that don't have
* the X509_get_signature_nid() function.
*/
#if defined(USE_OPENSSL) && defined(HAVE_X509_GET_SIGNATURE_NID)
#define HAVE_PGTLS_GET_PEER_CERTIFICATE_HASH
extern char *pgtls_get_peer_certificate_hash(PGconn *conn, size_t *len);
#endif
/*
* Verify that the server certificate matches the host name we connected to.

33
src/test/ssl/t/002_scram.pl
View File

@ -13,7 +13,7 @@ if ($ENV{with_openssl} ne 'yes')
plan skip_all => 'SSL not supported by this build';
}
my $number_of_tests = 6;
my $number_of_tests = 1;
# This is the hostname used to connect to the server.
my $SERVERHOSTADDR = '127.0.0.1';
@ -47,35 +47,6 @@ $common_connstr =
# Default settings
test_connect_ok($common_connstr, '',
"SCRAM authentication with default channel binding");
# Channel binding settings
test_connect_ok(
$common_connstr,
"scram_channel_binding=tls-unique",
"SCRAM authentication with tls-unique as channel binding");
test_connect_ok($common_connstr, "scram_channel_binding=''",
"SCRAM authentication without channel binding");
if ($supports_tls_server_end_point)
{
test_connect_ok(
$common_connstr,
"scram_channel_binding=tls-server-end-point",
"SCRAM authentication with tls-server-end-point as channel binding");
}
else
{
test_connect_fails(
$common_connstr,
"scram_channel_binding=tls-server-end-point",
qr/channel binding type "tls-server-end-point" is not supported by this build/,
"SCRAM authentication with tls-server-end-point as channel binding");
$number_of_tests++;
}
test_connect_fails(
$common_connstr,
"scram_channel_binding=not-exists",
qr/unsupported SCRAM channel-binding type/,
"SCRAM authentication with invalid channel binding");
"Basic SCRAM authentication with SSL");
done_testing($number_of_tests);