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jconwayjconway
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Add new function, PQchangePassword(), to libpq
Essentially this moves the non-interactive part of psql's "\password" command into an exported client function. The password is not sent to the server in cleartext because it is "encrypted" (in the case of scram and md5 it is actually hashed, but we have called these encrypted passwords for a long time now) on the client side. This is good because it ensures the cleartext password is never known by the server, and therefore won't end up in logs, pg_stat displays, etc. In other words, it exists for the same reason as PQencryptPasswordConn(), but is more convenient as it both builds and runs the "ALTER USER" command for you. PQchangePassword() uses PQencryptPasswordConn() to do the password encryption. PQencryptPasswordConn() is passed a NULL for the algorithm argument, hence encryption is done according to the server's password_encryption setting. Also modify the psql client to use the new function. That provides a builtin test case. Ultimately drivers built on top of libpq should expose this function and its use should be generally encouraged over doing ALTER USER directly for password changes. Author: Joe Conway Reviewed-by: Tom Lane Discussion: https://postgr.es/m/flat/b75955f7-e8cc-4bbd-817f-ef536bacbe93%40joeconway.com
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‎doc/src/sgml/libpq.sgml

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Original file line numberDiff line numberDiff line change
@@ -7116,6 +7116,45 @@ char *PQencryptPasswordConn(PGconn *conn, const char *passwd, const char *user,
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</listitem>
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</varlistentry>
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<varlistentry id="libpq-PQchangePassword">
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<term><function>PQchangePassword</function><indexterm><primary>PQchangePassword</primary></indexterm></term>
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<listitem>
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<para>
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Changes a <productname>PostgreSQL</productname> password.
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<synopsis>
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PGresult *PQchangePassword(PGconn *conn, const char *user, const char *passwd);
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</synopsis>
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This function uses <function>PQencryptPasswordConn</function>
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to build and execute the command <literal>ALTER USER ... PASSWORD
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'...'</literal>, thereby changing the user's password. It exists for
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the same reason as <function>PQencryptPasswordConn</function>, but
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is more convenient as it both builds and runs the command for you.
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<xref linkend="libpq-PQencryptPasswordConn"/> is passed a
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<symbol>NULL</symbol> for the algorithm argument, hence encryption is
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done according to the server's <xref linkend="guc-password-encryption"/>
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setting.
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</para>
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<para>
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The <parameter>user</parameter> and <parameter>passwd</parameter> arguments
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are the SQL name of the target user, and the new cleartext password.
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</para>
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<para>
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Returns a <structname>PGresult</structname> pointer representing
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the result of the <literal>ALTER USER</literal> command, or
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a null pointer if the routine failed before issuing any command.
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The <xref linkend="libpq-PQresultStatus"/> function should be called
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to check the return value for any errors (including the value of a null
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pointer, in which case it will return
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<symbol>PGRES_FATAL_ERROR</symbol>). Use
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<xref linkend="libpq-PQerrorMessage"/> to get more information about
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such errors.
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</para>
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</listitem>
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</varlistentry>
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<varlistentry id="libpq-PQencryptPassword">
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<term><function>PQencryptPassword</function><indexterm><primary>PQencryptPassword</primary></indexterm></term>
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‎src/bin/psql/command.c

Lines changed: 3 additions & 17 deletions
Original file line numberDiff line numberDiff line change
@@ -2158,29 +2158,15 @@ exec_command_password(PsqlScanState scan_state, bool active_branch)
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}
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else
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{
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char *encrypted_password;
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PGresult *res = PQchangePassword(pset.db, user, pw1);
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encrypted_password = PQencryptPasswordConn(pset.db, pw1, user, NULL);
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if (!encrypted_password)
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if (PQresultStatus(res) != PGRES_COMMAND_OK)
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{
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pg_log_info("%s", PQerrorMessage(pset.db));
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success = false;
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}
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else
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{
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PGresult *res;
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2174-
printfPQExpBuffer(&buf, "ALTER USER %s PASSWORD ",
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fmtId(user));
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appendStringLiteralConn(&buf, encrypted_password, pset.db);
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res = PSQLexec(buf.data);
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if (!res)
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success = false;
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else
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PQclear(res);
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PQfreemem(encrypted_password);
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}
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PQclear(res);
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}
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free(user);

‎src/interfaces/libpq/exports.txt

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Original file line numberDiff line numberDiff line change
@@ -191,3 +191,4 @@ PQclosePrepared 188
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PQclosePortal 189
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PQsendClosePrepared 190
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PQsendClosePortal 191
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PQchangePassword 192

‎src/interfaces/libpq/fe-auth.c

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Original file line numberDiff line numberDiff line change
@@ -1372,3 +1372,84 @@ PQencryptPasswordConn(PGconn *conn, const char *passwd, const char *user,
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return crypt_pwd;
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}
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/*
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* PQchangePassword -- exported routine to change a password
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*
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* This is intended to be used by client applications that wish to
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* change the password for a user. The password is not sent in
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* cleartext because it is encrypted on the client side. This is
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* good because it ensures the cleartext password is never known by
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* the server, and therefore won't end up in logs, pg_stat displays,
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* etc. The password encryption is performed by PQencryptPasswordConn(),
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* which is passed a NULL for the algorithm argument. Hence encryption
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* is done according to the server's password_encryption
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* setting. We export the function so that clients won't be dependent
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* on the implementation specific details with respect to how the
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* server changes passwords.
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*
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* Arguments are a connection object, the SQL name of the target user,
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* and the cleartext password.
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*
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* Return value is the PGresult of the executed ALTER USER statement
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* or NULL if we never get there. The caller is responsible to PQclear()
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* the returned PGresult.
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*
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* PQresultStatus() should be called to check the return value for errors,
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* and PQerrorMessage() used to get more information about such errors.
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*/
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PGresult *
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PQchangePassword(PGconn *conn, const char *user, const char *passwd)
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{
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char *encrypted_password = PQencryptPasswordConn(conn, passwd,
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user, NULL);
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if (!encrypted_password)
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{
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/* PQencryptPasswordConn() already registered the error */
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return NULL;
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}
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else
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{
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char *fmtpw = PQescapeLiteral(conn, encrypted_password,
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strlen(encrypted_password));
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/* no longer needed, so clean up now */
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PQfreemem(encrypted_password);
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if (!fmtpw)
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{
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/* PQescapeLiteral() already registered the error */
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return NULL;
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}
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else
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{
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char *fmtuser = PQescapeIdentifier(conn, user, strlen(user));
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if (!fmtuser)
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{
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/* PQescapeIdentifier() already registered the error */
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PQfreemem(fmtpw);
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return NULL;
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}
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else
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{
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PQExpBufferData buf;
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PGresult *res;
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initPQExpBuffer(&buf);
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printfPQExpBuffer(&buf, "ALTER USER %s PASSWORD %s",
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fmtuser, fmtpw);
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res = PQexec(conn, buf.data);
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/* clean up */
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termPQExpBuffer(&buf);
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PQfreemem(fmtuser);
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PQfreemem(fmtpw);
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return res;
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}
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}
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}
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}

‎src/interfaces/libpq/libpq-fe.h

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Original file line numberDiff line numberDiff line change
@@ -659,6 +659,7 @@ extern int PQenv2encoding(void);
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extern char *PQencryptPassword(const char *passwd, const char *user);
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extern char *PQencryptPasswordConn(PGconn *conn, const char *passwd, const char *user, const char *algorithm);
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extern PGresult *PQchangePassword(PGconn *conn, const char *user, const char *passwd);
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/* === in encnames.c === */
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