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libpq: Add min/max_protocol_version connection options

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All supported version of the PostgreSQL server send the
NegotiateProtocolVersion message when an unsupported minor protocol
version is requested by a client. But many other applications that
implement the PostgreSQL protocol (connection poolers, or other
databases) do not, and the same is true for PostgreSQL server versions
older than 9.3. Connecting to such other applications thus fails if a
client requests a protocol version different than 3.0.

This patch adds a max_protocol_version connection option to libpq that
specifies the protocol version that libpq should request from the
server. Currently only 3.0 is supported, but that will change in a
future commit that bumps the protocol version. Even after that version
bump the default will likely stay 3.0 for the time being. Once more of
the ecosystem supports the NegotiateProtocolVersion message we might
want to change the default to the latest minor version.

This also adds the similar min_protocol_version connection option, to
allow the client to specify that connecting should fail if a lower
protocol version is attempted by the server. This can be used to
ensure that certain protocol features are used, which can be
particularly useful if those features impact security.

Author: Jelte Fennema-Nio <postgres@jeltef.nl>
Reviewed-by: Robert Haas <robertmhaas@gmail.com> (earlier versions)
Discussion: https://www.postgresql.org/message-id/CAGECzQTfc_O%2BHXqAo5_-xG4r3EFVsTefUeQzSvhEyyLDba-O9w@mail.gmail.com
Discussion: https://www.postgresql.org/message-id/CAGECzQRbAGqJnnJJxTdKewTsNOovUt4bsx3NFfofz3m2j-t7tA@mail.gmail.com
This commit is contained in:
Heikki Linnakangas
2025-04-02 16:41:45 +03:00
parent 5070349102
commit 285613c60a
7 changed files with 315 additions and 12 deletions
Download Patch File Download Diff File Expand all files Collapse all files

68
doc/src/sgml/libpq.sgml
View File

@ -2144,6 +2144,54 @@ postgresql://%2Fvar%2Flib%2Fpostgresql/dbname
</listitem>
</varlistentry>
<varlistentry id="libpq-connect-min-protocol-version" xreflabel="min_protocol_version">
<term><literal>min_protocol_version</literal></term>
<listitem>
<para>
Specifies the minimum protocol version to allow for the connection.
The default is to allow any version of the
<productname>PostgreSQL</productname> protocol supported by libpq,
which currently means <literal>3.0</literal>. If the server
does not support at least this protocol version the connection will be
closed.
</para>
<para>
The current supported values are
<literal>3.0</literal>, <literal>3.2</literal>,
and <literal>latest</literal>. The <literal>latest</literal> value is
equivalent to the latest protocol version supported by the libpq
version being used, which is currently <literal>3.2</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry id="libpq-connect-max-protocol-version" xreflabel="max_protocol_version">
<term><literal>max_protocol_version</literal></term>
<listitem>
<para>
Specifies the protocol version to request from the server.
The default is to use version <literal>3.0</literal> of the
<productname>PostgreSQL</productname> protocol, unless the connection
string specifies a feature that relies on a higher protocol version,
in which case the latest version supported by libpq is used. If the
server does not support the protocol version requested by the client,
the connection is automatically downgraded to a lower minor protocol
version that the server supports. After the connection attempt has
completed you can use <xref linkend="libpq-PQprotocolVersion"/> to
find out which exact protocol version was negotiated.
</para>
<para>
The current supported values are
<literal>3.0</literal>, <literal>3.2</literal>,
and <literal>latest</literal>. The <literal>latest</literal> value is
equivalent to the latest protocol version supported by the libpq
version being used, which is currently <literal>3.2</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry id="libpq-connect-ssl-max-protocol-version" xreflabel="ssl_max_protocol_version">
<term><literal>ssl_max_protocol_version</literal></term>
<listitem>
@ -9329,6 +9377,26 @@ myEventProc(PGEventId evtId, void *evtInfo, void *passThrough)
linkend="libpq-connect-load-balance-hosts"/> connection parameter.
</para>
</listitem>
<listitem>
<para>
<indexterm>
<primary><envar>PGMINPROTOCOLVERSION</envar></primary>
</indexterm>
<envar>PGMINPROTOCOLVERSION</envar> behaves the same as the <xref
linkend="libpq-connect-min-protocol-version"/> connection parameter.
</para>
</listitem>
<listitem>
<para>
<indexterm>
<primary><envar>PGMAXPROTOCOLVERSION</envar></primary>
</indexterm>
<envar>PGMAXPROTOCOLVERSION</envar> behaves the same as the <xref
linkend="libpq-connect-max-protocol-version"/> connection parameter.
</para>
</listitem>
</itemizedlist>
</para>

33
doc/src/sgml/protocol.sgml
View File

@ -18,17 +18,23 @@
</para>
<para>
This document describes version 3.0 of the protocol, implemented in
<productname>PostgreSQL</productname> 7.4 and later. For descriptions
of the earlier protocol versions, see previous releases of the
<productname>PostgreSQL</productname> documentation. A single server
This document describes version 3.2 of the protocol, introduced in
<productname>PostgreSQL</productname> version 18. The server and the libpq
client library are backwards compatible with protocol version 3.0,
implemented in <productname>PostgreSQL</productname> 7.4 and later.
For descriptions of earlier protocol versions, see previous releases of the
<productname>PostgreSQL</productname> documentation.
</para>
<para>
A single server
can support multiple protocol versions. The initial startup-request
message tells the server which protocol version the client is attempting to
use. If the major version requested by the client is not supported by
the server, the connection will be rejected (for example, this would occur
if the client requested protocol version 4.0, which does not exist as of
this writing). If the minor version requested by the client is not
supported by the server (e.g., the client requests version 3.1, but the
supported by the server (e.g., the client requests version 3.2, but the
server supports only 3.0), the server may either reject the connection or
may respond with a NegotiateProtocolVersion message containing the highest
minor protocol version which it supports. The client may then choose either
@ -36,6 +42,13 @@
to abort the connection.
</para>
<para>
The protocol negotiation was introduced in
<productname>PostgreSQL</productname> version 9.3.21. Earlier versions would
reject the connection if the client requested a minor version that was not
supported by the server.
</para>
<para>
In order to serve multiple clients efficiently, the server launches
a new <quote>backend</quote> process for each client.
@ -413,8 +426,14 @@
this message indicates the highest supported minor version. This
message will also be sent if the client requested unsupported protocol
options (i.e., beginning with <literal>_pq_.</literal>) in the
startup packet. This message will be followed by an ErrorResponse or
a message indicating the success or failure of authentication.
startup packet.
</para>
<para>
After this message, the authentication will continue using the version
indicated by the server. If the client does not support the older
version, it should immediately close the connection. If the server
does not send this message, it supports the client's requested
protocol version and all the protocol options.
</para>
</listitem>
</varlistentry>

3
src/include/libpq/pqcomm.h
View File

@ -91,11 +91,10 @@ is_unixsock_path(const char *path)
/*
* The earliest and latest frontend/backend protocol version supported.
* (Only protocol version 3 is currently supported)
*/
#define PG_PROTOCOL_EARLIEST PG_PROTOCOL(3,0)
#define PG_PROTOCOL_LATEST PG_PROTOCOL(3,0)
#define PG_PROTOCOL_LATEST PG_PROTOCOL(3,2)
typedef uint32 ProtocolVersion; /* FE/BE protocol version number */

88
src/interfaces/libpq/fe-connect.c
View File

@ -325,6 +325,16 @@ static const internalPQconninfoOption PQconninfoOptions[] = {
"Require-Auth", "", 14, /* sizeof("scram-sha-256") == 14 */
offsetof(struct pg_conn, require_auth)},
{"min_protocol_version", "PGMINPROTOCOLVERSION",
NULL, NULL,
"Min-Protocol-Version", "", 6, /* sizeof("latest") = 6 */
offsetof(struct pg_conn, min_protocol_version)},
{"max_protocol_version", "PGMAXPROTOCOLVERSION",
NULL, NULL,
"Max-Protocol-Version", "", 6, /* sizeof("latest") = 6 */
offsetof(struct pg_conn, max_protocol_version)},
{"ssl_min_protocol_version", "PGSSLMINPROTOCOLVERSION", "TLSv1.2", NULL,
"SSL-Minimum-Protocol-Version", "", 8, /* sizeof("TLSv1.x") == 8 */
offsetof(struct pg_conn, ssl_min_protocol_version)},
@ -483,6 +493,7 @@ static void pgpassfileWarning(PGconn *conn);
static void default_threadlock(int acquire);
static bool sslVerifyProtocolVersion(const char *version);
static bool sslVerifyProtocolRange(const char *min, const char *max);
static bool pqParseProtocolVersion(const char *value, ProtocolVersion *result, PGconn *conn, const char *context);
/* global variable because fe-auth.c needs to access it */
@ -2081,6 +2092,48 @@ pqConnectOptions2(PGconn *conn)
}
}
if (conn->min_protocol_version)
{
if (!pqParseProtocolVersion(conn->min_protocol_version, &conn->min_pversion, conn, "min_protocol_version"))
{
conn->status = CONNECTION_BAD;
return false;
}
}
else
{
conn->min_pversion = PG_PROTOCOL_EARLIEST;
}
if (conn->max_protocol_version)
{
if (!pqParseProtocolVersion(conn->max_protocol_version, &conn->max_pversion, conn, "max_protocol_version"))
{
conn->status = CONNECTION_BAD;
return false;
}
}
else
{
/*
* To not break connecting to older servers/poolers that do not yet
* support NegotiateProtocolVersion, default to the 3.0 protocol at
* least for a while longer. Except when min_protocol_version is set
* to something larger, then we might as well default to the latest.
*/
if (conn->min_pversion > PG_PROTOCOL(3, 0))
conn->max_pversion = PG_PROTOCOL_LATEST;
else
conn->max_pversion = PG_PROTOCOL(3, 0);
}
if (conn->min_pversion > conn->max_pversion)
{
conn->status = CONNECTION_BAD;
libpq_append_conn_error(conn, "min_protocol_version is greater than max_protocol_version");
return false;
}
/*
* Resolve special "auto" client_encoding from the locale
*/
@ -3084,7 +3137,7 @@ keep_going: /* We will come back to here until there is
* must persist across individual connection attempts, but we must
* reset them when we start to consider a new server.
*/
conn->pversion = PG_PROTOCOL(3, 0);
conn->pversion = conn->max_pversion;
conn->send_appname = true;
conn->failed_enc_methods = 0;
conn->current_enc_method = 0;
@ -4102,6 +4155,7 @@ keep_going: /* We will come back to here until there is
/* OK, we read the message; mark data consumed */
pqParseDone(conn, conn->inCursor);
goto keep_going;
}
@ -8157,6 +8211,38 @@ error:
return false;
}
/*
* Parse and try to interpret "value" as a ProtocolVersion value, and if
* successful, store it in *result.
*/
static bool
pqParseProtocolVersion(const char *value, ProtocolVersion *result, PGconn *conn,
const char *context)
{
if (strcmp(value, "latest") == 0)
{
*result = PG_PROTOCOL_LATEST;
return true;
}
if (strcmp(value, "3.0") == 0)
{
*result = PG_PROTOCOL(3, 0);
return true;
}
/* 3.1 never existed, we went straight from 3.0 to 3.2 */
if (strcmp(value, "3.2") == 0)
{
*result = PG_PROTOCOL(3, 2);
return true;
}
libpq_append_conn_error(conn, "invalid %s value: \"%s\"",
context, value);
return false;
}
/*
* To keep the API consistent, the locking stubs are always provided, even
* if they are not required.

18
src/interfaces/libpq/fe-protocol3.c
View File

@ -1432,6 +1432,13 @@ pqGetNegotiateProtocolVersion3(PGconn *conn)
goto failure;
}
/* 3.1 never existed, we went straight from 3.0 to 3.2 */
if (their_version == PG_PROTOCOL(3, 1))
{
libpq_append_conn_error(conn, "received invalid protocol negotiation message: server requests downgrade to non-existent 3.1 protocol version");
goto failure;
}
if (num < 0)
{
libpq_append_conn_error(conn, "received invalid protocol negotiation message: server reported negative number of unsupported parameters");
@ -1444,6 +1451,17 @@ pqGetNegotiateProtocolVersion3(PGconn *conn)
goto failure;
}
if (their_version < conn->min_pversion)
{
libpq_append_conn_error(conn, "server only supports protocol version %d.%d, but min_protocol_version was set to %d.%d",
PG_PROTOCOL_MAJOR(their_version),
PG_PROTOCOL_MINOR(their_version),
PG_PROTOCOL_MAJOR(conn->min_pversion),
PG_PROTOCOL_MINOR(conn->min_pversion));
goto failure;
}
/* the version is acceptable */
conn->pversion = their_version;

4
src/interfaces/libpq/libpq-int.h
View File

@ -417,6 +417,8 @@ struct pg_conn
char *gsslib; /* What GSS library to use ("gssapi" or
* "sspi") */
char *gssdelegation; /* Try to delegate GSS credentials? (0 or 1) */
char *min_protocol_version; /* minimum used protocol version */
char *max_protocol_version; /* maximum used protocol version */
char *ssl_min_protocol_version; /* minimum TLS protocol version */
char *ssl_max_protocol_version; /* maximum TLS protocol version */
char *target_session_attrs; /* desired session properties */
@ -539,6 +541,8 @@ struct pg_conn
void *scram_client_key_binary; /* binary SCRAM client key */
size_t scram_server_key_len;
void *scram_server_key_binary; /* binary SCRAM server key */
ProtocolVersion min_pversion; /* protocol version to request */
ProtocolVersion max_pversion; /* protocol version to request */
/* Miscellaneous stuff */
int be_pid; /* PID of backend --- needed for cancels */

113
src/test/modules/libpq_pipeline/libpq_pipeline.c
View File

@ -206,15 +206,17 @@ copy_connection(PGconn *conn)
PQconninfoOption *opts = PQconninfo(conn);
const char **keywords;
const char **vals;
int nopts = 1;
int i = 0;
int nopts = 0;
int i;
for (PQconninfoOption *opt = opts; opt->keyword != NULL; ++opt)
nopts++;
nopts++; /* for the NULL terminator */
keywords = pg_malloc(sizeof(char *) * nopts);
vals = pg_malloc(sizeof(char *) * nopts);
i = 0;
for (PQconninfoOption *opt = opts; opt->keyword != NULL; ++opt)
{
if (opt->val)
@ -1405,6 +1407,110 @@ test_prepared(PGconn *conn)
fprintf(stderr, "ok\n");
}
/*
* Test max_protocol_version options.
*/
static void
test_protocol_version(PGconn *conn)
{
const char **keywords;
const char **vals;
int nopts;
PQconninfoOption *opts = PQconninfo(conn);
int protocol_version;
int max_protocol_version_index;
int i;
/*
* Prepare keywords/vals arrays, copied from the existing connection, with
* an extra slot for 'max_protocol_version'.
*/
nopts = 0;
for (PQconninfoOption *opt = opts; opt->keyword != NULL; ++opt)
nopts++;
nopts++; /* max_protocol_version */
nopts++; /* NULL terminator */
keywords = pg_malloc0(sizeof(char *) * nopts);
vals = pg_malloc0(sizeof(char *) * nopts);
i = 0;
for (PQconninfoOption *opt = opts; opt->keyword != NULL; ++opt)
{
if (opt->val)
{
keywords[i] = opt->keyword;
vals[i] = opt->val;
i++;
}
}
max_protocol_version_index = i;
keywords[i] = "max_protocol_version"; /* value is filled in below */
i++;
keywords[i] = vals[i] = NULL;
/*
* Test max_protocol_version=3.0
*/
vals[max_protocol_version_index] = "3.0";
conn = PQconnectdbParams(keywords, vals, false);
if (PQstatus(conn) != CONNECTION_OK)
pg_fatal("Connection to database failed: %s",
PQerrorMessage(conn));
protocol_version = PQfullProtocolVersion(conn);
if (protocol_version != 30000)
pg_fatal("expected 30000, got %d", protocol_version);
PQfinish(conn);
/*
* Test max_protocol_version=3.1. It's not valid, we went straight from
* 3.0 to 3.2.
*/
vals[max_protocol_version_index] = "3.1";
conn = PQconnectdbParams(keywords, vals, false);
if (PQstatus(conn) != CONNECTION_BAD)
pg_fatal("Connecting with max_protocol_version 3.1 should have failed.");
PQfinish(conn);
/*
* Test max_protocol_version=3.2
*/
vals[max_protocol_version_index] = "3.2";
conn = PQconnectdbParams(keywords, vals, false);
if (PQstatus(conn) != CONNECTION_OK)
pg_fatal("Connection to database failed: %s",
PQerrorMessage(conn));
protocol_version = PQfullProtocolVersion(conn);
if (protocol_version != 30002)
pg_fatal("expected 30002, got %d", protocol_version);
PQfinish(conn);
/*
* Test max_protocol_version=latest. 'latest' currently means '3.2'.
*/
vals[max_protocol_version_index] = "latest";
conn = PQconnectdbParams(keywords, vals, false);
if (PQstatus(conn) != CONNECTION_OK)
pg_fatal("Connection to database failed: %s",
PQerrorMessage(conn));
protocol_version = PQfullProtocolVersion(conn);
if (protocol_version != 30002)
pg_fatal("expected 30002, got %d", protocol_version);
PQfinish(conn);
}
/* Notice processor: print notices, and count how many we got */
static void
notice_processor(void *arg, const char *message)
@ -2153,6 +2259,7 @@ print_test_list(void)
printf("pipeline_idle\n");
printf("pipelined_insert\n");
printf("prepared\n");
printf("protocol_version\n");
printf("simple_pipeline\n");
printf("singlerow\n");
printf("transaction\n");
@ -2263,6 +2370,8 @@ main(int argc, char **argv)
test_pipelined_insert(conn, numrows);
else if (strcmp(testname, "prepared") == 0)
test_prepared(conn);
else if (strcmp(testname, "protocol_version") == 0)
test_protocol_version(conn);
else if (strcmp(testname, "simple_pipeline") == 0)
test_simple_pipeline(conn);
else if (strcmp(testname, "singlerow") == 0)