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Remove support for tls-unique channel binding.

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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
Download Patch File Download Diff File Expand all files Collapse all files

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,," */