Remove support for password_encryption='off' / 'plain'.

Storing passwords in plaintext hasn't been a good idea for a very long
time, if ever. Now seems like a good time to finally forbid it, since we're
messing with this in PostgreSQL 10 anyway.

Remove the CREATE/ALTER USER UNENCRYPTED PASSSWORD 'foo' syntax, since
storing passwords unencrypted is no longer supported. ENCRYPTED PASSWORD
'foo' is still accepted, but ENCRYPTED is now just a noise-word, it does
the same as just PASSWORD 'foo'.

Likewise, remove the --unencrypted option from createuser, but accept
--encrypted as a no-op for backward compatibility. AFAICS, --encrypted was
a no-op even before this patch, because createuser encrypted the password
before sending it to the server even if --encrypted was not specified. It
added the ENCRYPTED keyword to the SQL command, but since the password was
already in encrypted form, it didn't make any difference. The documentation
was not clear on whether that was intended or not, but it's moot now.

Also, while password_encryption='on' is still accepted as an alias for
'md5', it is now marked as hidden, so that it is not listed as an accepted
value in error hints, for example. That's not directly related to removing
'plain', but it seems better this way.

Reviewed by Michael Paquier

Discussion: https://www.postgresql.org/message-id/16e9b768-fd78-0b12-cfc1-7b6b7f238fde@iki.fi

1 files changed, 38 insertions, 88 deletions

diff --git a/src/backend/libpq/crypt.c b/src/backend/libpq/crypt.c
index 9fe79b48946..e7a6b04fb5a 100644
--- a/src/backend/libpq/crypt.c
+++ b/src/backend/libpq/crypt.c
@@ -109,9 +109,8 @@ get_password_type(const char *shadow_pass)
  * Given a user-supplied password, convert it into a verifier of
  * 'target_type' kind.
  *
- * If the password looks like a valid MD5 hash, it is stored as it is.
- * We cannot reverse the hash, so even if the caller requested a plaintext
- * plaintext password, the MD5 hash is returned.
+ * If the password is already in encrypted form, we cannot reverse the
+ * hash, so it is stored as it is regardless of the requested type.
  */
 char *
 encrypt_password(PasswordType target_type, const char *role,
@@ -120,54 +119,30 @@ encrypt_password(PasswordType target_type, const char *role,
 	PasswordType guessed_type = get_password_type(password);
 	char	   *encrypted_password;
 
-	switch (target_type)
+	if (guessed_type != PASSWORD_TYPE_PLAINTEXT)
 	{
-		case PASSWORD_TYPE_PLAINTEXT:
-
-			/*
-			 * We cannot convert a hashed password back to plaintext, so just
-			 * store the password as it was, whether it was hashed or not.
-			 */
-			return pstrdup(password);
+		/*
+		 * Cannot convert an already-encrypted password from one
+		 * format to another, so return it as it is.
+		 */
+		return pstrdup(password);
+	}
 
+	switch (target_type)
+	{
 		case PASSWORD_TYPE_MD5:
-			switch (guessed_type)
-			{
-				case PASSWORD_TYPE_PLAINTEXT:
-					encrypted_password = palloc(MD5_PASSWD_LEN + 1);
-
-					if (!pg_md5_encrypt(password, role, strlen(role),
-										encrypted_password))
-						elog(ERROR, "password encryption failed");
-					return encrypted_password;
+			encrypted_password = palloc(MD5_PASSWD_LEN + 1);
 
-				case PASSWORD_TYPE_SCRAM_SHA_256:
-
-					/*
-					 * cannot convert a SCRAM verifier to an MD5 hash, so fall
-					 * through to save the SCRAM verifier instead.
-					 */
-				case PASSWORD_TYPE_MD5:
-					return pstrdup(password);
-			}
-			break;
+			if (!pg_md5_encrypt(password, role, strlen(role),
+								encrypted_password))
+				elog(ERROR, "password encryption failed");
+			return encrypted_password;
 
 		case PASSWORD_TYPE_SCRAM_SHA_256:
-			switch (guessed_type)
-			{
-				case PASSWORD_TYPE_PLAINTEXT:
-					return pg_be_scram_build_verifier(password);
-
-				case PASSWORD_TYPE_MD5:
+			return pg_be_scram_build_verifier(password);
 
-					/*
-					 * cannot convert an MD5 hash to a SCRAM verifier, so fall
-					 * through to save the MD5 hash instead.
-					 */
-				case PASSWORD_TYPE_SCRAM_SHA_256:
-					return pstrdup(password);
-			}
-			break;
+		case PASSWORD_TYPE_PLAINTEXT:
+			elog(ERROR, "cannot encrypt password with 'plaintext'");
 	}
 
 	/*
@@ -197,10 +172,17 @@ md5_crypt_verify(const char *role, const char *shadow_pass,
 {
 	int			retval;
 	char		crypt_pwd[MD5_PASSWD_LEN + 1];
-	char		crypt_pwd2[MD5_PASSWD_LEN + 1];
 
 	Assert(md5_salt_len > 0);
 
+	if (get_password_type(shadow_pass) != PASSWORD_TYPE_MD5)
+	{
+		/* incompatible password hash format. */
+		*logdetail = psprintf(_("User \"%s\" has a password that cannot be used with MD5 authentication."),
+							  role);
+		return STATUS_ERROR;
+	}
+
 	/*
 	 * Compute the correct answer for the MD5 challenge.
 	 *
@@ -208,40 +190,12 @@ md5_crypt_verify(const char *role, const char *shadow_pass,
 	 * below: the only possible error is out-of-memory, which is unlikely, and
 	 * if it did happen adding a psprintf call would only make things worse.
 	 */
-	switch (get_password_type(shadow_pass))
+	/* stored password already encrypted, only do salt */
+	if (!pg_md5_encrypt(shadow_pass + strlen("md5"),
+						md5_salt, md5_salt_len,
+						crypt_pwd))
 	{
-		case PASSWORD_TYPE_MD5:
-			/* stored password already encrypted, only do salt */
-			if (!pg_md5_encrypt(shadow_pass + strlen("md5"),
-								md5_salt, md5_salt_len,
-								crypt_pwd))
-			{
-				return STATUS_ERROR;
-			}
-			break;
-
-		case PASSWORD_TYPE_PLAINTEXT:
-			/* stored password is plain, double-encrypt */
-			if (!pg_md5_encrypt(shadow_pass,
-								role,
-								strlen(role),
-								crypt_pwd2))
-			{
-				return STATUS_ERROR;
-			}
-			if (!pg_md5_encrypt(crypt_pwd2 + strlen("md5"),
-								md5_salt, md5_salt_len,
-								crypt_pwd))
-			{
-				return STATUS_ERROR;
-			}
-			break;
-
-		default:
-			/* unknown password hash format. */
-			*logdetail = psprintf(_("User \"%s\" has a password that cannot be used with MD5 authentication."),
-								  role);
-			return STATUS_ERROR;
+		return STATUS_ERROR;
 	}
 
 	if (strcmp(client_pass, crypt_pwd) == 0)
@@ -259,8 +213,8 @@ md5_crypt_verify(const char *role, const char *shadow_pass,
 /*
  * Check given password for given user, and return STATUS_OK or STATUS_ERROR.
  *
- * 'shadow_pass' is the user's correct password or password hash, as stored
- * in pg_authid.rolpassword.
+ * 'shadow_pass' is the user's correct password hash, as stored in
+ * pg_authid.rolpassword.
  * 'client_pass' is the password given by the remote user.
  *
  * In the error case, optionally store a palloc'd string at *logdetail
@@ -320,14 +274,10 @@ plain_crypt_verify(const char *role, const char *shadow_pass,
 			break;
 
 		case PASSWORD_TYPE_PLAINTEXT:
-			if (strcmp(client_pass, shadow_pass) == 0)
-				return STATUS_OK;
-			else
-			{
-				*logdetail = psprintf(_("Password does not match for user \"%s\"."),
-									  role);
-				return STATUS_ERROR;
-			}
+			/*
+			 * We never store passwords in plaintext, so this shouldn't
+			 * happen.
+			 */
 			break;
 	}