Fix detection of passwords hashed with MD5 or SCRAM-SHA-256

This commit fixes a couple of issues related to the way password
verifiers hashed with MD5 or SCRAM-SHA-256 are detected, leading to
being able to store in catalogs passwords which do not follow the
supported hash formats:
- A MD5-hashed entry was checked based on if its header uses "md5" and
if the string length matches what is expected.  Unfortunately the code
never checked if the hash only used hexadecimal characters, as reported
by Tom Lane.
- A SCRAM-hashed entry was checked based on only its header, which
should be "SCRAM-SHA-256$", but it never checked for any fields
afterwards, as reported by Jonathan Katz.

Backpatch down to v10, which is where SCRAM has been introduced, and
where password verifiers in plain format have been removed.

Author: Jonathan Katz
Reviewed-by: Tom Lane, Michael Paquier
Discussion: https://postgr.es/m/016deb6b-1f0a-8e9f-1833-a8675b170aa9@postgresql.org
Backpatch-through: 10

src/backend/libpq/auth-scram.c

@@ -161,8 +161,6 @@ static char *build_server_first_message(scram_state *state);
 static char *build_server_final_message(scram_state *state);
 static bool verify_client_proof(scram_state *state);
 static bool verify_final_nonce(scram_state *state);
-static bool parse_scram_verifier(const char *verifier, int *iterations,
-					 char **salt, uint8 *stored_key, uint8 *server_key);
 static void mock_scram_verifier(const char *username, int *iterations,
 					char **salt, uint8 *stored_key, uint8 *server_key);
 static bool is_scram_printable(char *p);
@@ -546,7 +544,7 @@ scram_verify_plain_password(const char *username, const char *password,
  *
  * Returns true if the SCRAM verifier has been parsed, and false otherwise.
  */
-static bool
+bool
 parse_scram_verifier(const char *verifier, int *iterations, char **salt,
 					 uint8 *stored_key, uint8 *server_key)
 {

src/backend/libpq/crypt.c

@@ -20,6 +20,7 @@
 
 #include "catalog/pg_authid.h"
 #include "common/md5.h"
+#include "common/scram-common.h"
 #include "libpq/crypt.h"
 #include "libpq/scram.h"
 #include "miscadmin.h"
@@ -90,9 +91,17 @@ get_role_password(const char *role, char **logdetail)
 PasswordType
 get_password_type(const char *shadow_pass)
 {
-	if (strncmp(shadow_pass, "md5", 3) == 0 && strlen(shadow_pass) == MD5_PASSWD_LEN)
+	char	   *encoded_salt;
+	int			iterations;
+	uint8		stored_key[SCRAM_KEY_LEN];
+	uint8		server_key[SCRAM_KEY_LEN];
+
+	if (strncmp(shadow_pass, "md5", 3) == 0 &&
+		strlen(shadow_pass) == MD5_PASSWD_LEN &&
+		strspn(shadow_pass + 3, MD5_PASSWD_CHARSET) == MD5_PASSWD_LEN - 3)
 		return PASSWORD_TYPE_MD5;
-	if (strncmp(shadow_pass, "SCRAM-SHA-256$", strlen("SCRAM-SHA-256$")) == 0)
+	if (parse_scram_verifier(shadow_pass, &iterations, &encoded_salt,
+							 stored_key, server_key))
 		return PASSWORD_TYPE_SCRAM_SHA_256;
 	return PASSWORD_TYPE_PLAINTEXT;
 }

src/include/common/md5.h

@@ -16,6 +16,7 @@
 #ifndef PG_MD5_H
 #define PG_MD5_H
 
+#define MD5_PASSWD_CHARSET	"0123456789abcdef"
 #define MD5_PASSWD_LEN	35
 
 extern bool pg_md5_hash(const void *buff, size_t len, char *hexsum);

src/include/libpq/scram.h

@@ -29,6 +29,8 @@ extern int pg_be_scram_exchange(void *opaq, const char *input, int inputlen,
 
 /* Routines to handle and check SCRAM-SHA-256 verifier */
 extern char *pg_be_scram_build_verifier(const char *password);
+extern bool parse_scram_verifier(const char *verifier, int *iterations, char **salt,
+					 uint8 *stored_key, uint8 *server_key);
 extern bool scram_verify_plain_password(const char *username,
 							const char *password, const char *verifier);
 

src/test/regress/expected/password.out

@@ -62,6 +62,15 @@ SET password_encryption = 'scram-sha-256';
 ALTER ROLE  regress_passwd4 PASSWORD 'foo';
 -- already encrypted with MD5, use as it is
 CREATE ROLE regress_passwd5 PASSWORD 'md5e73a4b11df52a6068f8b39f90be36023';
+-- This looks like a valid SCRAM-SHA-256 verifier, but it is not
+-- so it should be hashed with SCRAM-SHA-256.
+CREATE ROLE regress_passwd6 PASSWORD 'SCRAM-SHA-256$1234';
+-- These may look like valid MD5 verifiers, but they are not, so they
+-- should be hashed with SCRAM-SHA-256.
+-- trailing garbage at the end
+CREATE ROLE regress_passwd7 PASSWORD 'md5012345678901234567890123456789zz';
+-- invalid length
+CREATE ROLE regress_passwd8 PASSWORD 'md501234567890123456789012345678901zz';
 SELECT rolname, regexp_replace(rolpassword, '(SCRAM-SHA-256)\$(\d+):([a-zA-Z0-9+/=]+)\$([a-zA-Z0-9+=/]+):([a-zA-Z0-9+/=]+)', '\1$\2:<salt>$<storedkey>:<serverkey>') as rolpassword_masked
     FROM pg_authid
     WHERE rolname LIKE 'regress_passwd%'
@@ -73,7 +82,10 @@ SELECT rolname, regexp_replace(rolpassword, '(SCRAM-SHA-256)\$(\d+):([a-zA-Z0-9+
  regress_passwd3 | SCRAM-SHA-256$4096:<salt>$<storedkey>:<serverkey>
  regress_passwd4 | SCRAM-SHA-256$4096:<salt>$<storedkey>:<serverkey>
  regress_passwd5 | md5e73a4b11df52a6068f8b39f90be36023
-(5 rows)
+ regress_passwd6 | SCRAM-SHA-256$4096:<salt>$<storedkey>:<serverkey>
+ regress_passwd7 | SCRAM-SHA-256$4096:<salt>$<storedkey>:<serverkey>
+ regress_passwd8 | SCRAM-SHA-256$4096:<salt>$<storedkey>:<serverkey>
+(8 rows)
 
 -- An empty password is not allowed, in any form
 CREATE ROLE regress_passwd_empty PASSWORD '';
@@ -93,6 +105,9 @@ DROP ROLE regress_passwd2;
 DROP ROLE regress_passwd3;
 DROP ROLE regress_passwd4;
 DROP ROLE regress_passwd5;
+DROP ROLE regress_passwd6;
+DROP ROLE regress_passwd7;
+DROP ROLE regress_passwd8;
 DROP ROLE regress_passwd_empty;
 -- all entries should have been removed
 SELECT rolname, rolpassword

src/test/regress/sql/password.sql

@@ -54,6 +54,16 @@ ALTER ROLE  regress_passwd4 PASSWORD 'foo';
 -- already encrypted with MD5, use as it is
 CREATE ROLE regress_passwd5 PASSWORD 'md5e73a4b11df52a6068f8b39f90be36023';
 
+-- This looks like a valid SCRAM-SHA-256 verifier, but it is not
+-- so it should be hashed with SCRAM-SHA-256.
+CREATE ROLE regress_passwd6 PASSWORD 'SCRAM-SHA-256$1234';
+-- These may look like valid MD5 verifiers, but they are not, so they
+-- should be hashed with SCRAM-SHA-256.
+-- trailing garbage at the end
+CREATE ROLE regress_passwd7 PASSWORD 'md5012345678901234567890123456789zz';
+-- invalid length
+CREATE ROLE regress_passwd8 PASSWORD 'md501234567890123456789012345678901zz';
+
 SELECT rolname, regexp_replace(rolpassword, '(SCRAM-SHA-256)\$(\d+):([a-zA-Z0-9+/=]+)\$([a-zA-Z0-9+=/]+):([a-zA-Z0-9+/=]+)', '\1$\2:<salt>$<storedkey>:<serverkey>') as rolpassword_masked
     FROM pg_authid
     WHERE rolname LIKE 'regress_passwd%'
@@ -70,6 +80,9 @@ DROP ROLE regress_passwd2;
 DROP ROLE regress_passwd3;
 DROP ROLE regress_passwd4;
 DROP ROLE regress_passwd5;
+DROP ROLE regress_passwd6;
+DROP ROLE regress_passwd7;
+DROP ROLE regress_passwd8;
 DROP ROLE regress_passwd_empty;
 
 -- all entries should have been removed