From 930b785d40cf53d679c72ffc2c34a63d412bee5b Mon Sep 17 00:00:00 2001
From: Tom Lane <tgl@sss.pgh.pa.us>
Date: Sat, 8 Sep 2018 18:20:36 -0400
Subject: [PATCH] Minor cleanup/future-proofing for pg_saslprep().

Ensure that pg_saslprep() initializes its output argument to NULL in
all failure paths, and then remove the redundant initialization that
some (not all) of its callers did.  This does not fix any live bug,
but it reduces the odds of future bugs of omission.

Also add a comment about why the existing failure-path coding is
adequate.

Back-patch so as to keep the function's API consistent across branches,
again to forestall future bug introduction.

Patch by me, reviewed by Michael Paquier

Discussion: https://postgr.es/m/16558.1536407783@sss.pgh.pa.us
---
 src/backend/libpq/auth-scram.c       |  4 ++--
 src/common/saslprep.c                | 11 ++++++++---
 src/interfaces/libpq/fe-auth-scram.c |  2 +-
 3 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/src/backend/libpq/auth-scram.c b/src/backend/libpq/auth-scram.c
index 7cd31ebe8e2..d69d7dde06a 100644
--- a/src/backend/libpq/auth-scram.c
+++ b/src/backend/libpq/auth-scram.c
@@ -382,7 +382,7 @@ pg_be_scram_exchange(void *opaq, char *input, int inputlen,
 char *
 pg_be_scram_build_verifier(const char *password)
 {
-	char	   *prep_password = NULL;
+	char	   *prep_password;
 	pg_saslprep_rc rc;
 	char		saltbuf[SCRAM_DEFAULT_SALT_LEN];
 	char	   *result;
@@ -428,7 +428,7 @@ scram_verify_plain_password(const char *username, const char *password,
 	uint8		stored_key[SCRAM_KEY_LEN];
 	uint8		server_key[SCRAM_KEY_LEN];
 	uint8		computed_key[SCRAM_KEY_LEN];
-	char	   *prep_password = NULL;
+	char	   *prep_password;
 	pg_saslprep_rc rc;
 
 	if (!parse_scram_verifier(verifier, &iterations, &encoded_salt,
diff --git a/src/common/saslprep.c b/src/common/saslprep.c
index 0a3585850b8..32efc31591e 100644
--- a/src/common/saslprep.c
+++ b/src/common/saslprep.c
@@ -1081,6 +1081,9 @@ pg_saslprep(const char *input, char **output)
 	unsigned char *p;
 	pg_wchar   *wp;
 
+	/* Ensure we return *output as NULL on failure */
+	*output = NULL;
+
 	/* Check that the password isn't stupendously long */
 	if (strlen(input) > MAX_PASSWORD_LENGTH)
 	{
@@ -1112,10 +1115,7 @@ pg_saslprep(const char *input, char **output)
 	 */
 	input_size = pg_utf8_string_len(input);
 	if (input_size < 0)
-	{
-		*output = NULL;
 		return SASLPREP_INVALID_UTF8;
-	}
 
 	input_chars = ALLOC((input_size + 1) * sizeof(pg_wchar));
 	if (!input_chars)
@@ -1246,6 +1246,11 @@ pg_saslprep(const char *input, char **output)
 	result = ALLOC(result_size + 1);
 	if (!result)
 		goto oom;
+
+	/*
+	 * There are no error exits below here, so the error exit paths don't need
+	 * to worry about possibly freeing "result".
+	 */
 	p = (unsigned char *) result;
 	for (wp = output_chars; *wp; wp++)
 	{
diff --git a/src/interfaces/libpq/fe-auth-scram.c b/src/interfaces/libpq/fe-auth-scram.c
index edfd42df854..7fa7f34c80b 100644
--- a/src/interfaces/libpq/fe-auth-scram.c
+++ b/src/interfaces/libpq/fe-auth-scram.c
@@ -621,7 +621,7 @@ verify_server_signature(fe_scram_state *state)
 char *
 pg_fe_scram_build_verifier(const char *password)
 {
-	char	   *prep_password = NULL;
+	char	   *prep_password;
 	pg_saslprep_rc rc;
 	char		saltbuf[SCRAM_DEFAULT_SALT_LEN];
 	char	   *result;