Fix inconsistent quoting of role names in ACLs.

getid() and putid(), which parse and deparse role names within ACL
input/output, applied isalnum() to see if a character within a role
name requires quoting.  They did this even for non-ASCII characters,
which is problematic because the results would depend on encoding,
locale, and perhaps even platform.  So it's possible that putid()
could elect not to quote some string that, later in some other
environment, getid() will decide is not a valid identifier, causing
dump/reload or similar failures.

To fix this in a way that won't risk interoperability problems
with unpatched versions, make getid() treat any non-ASCII as a
legitimate identifier character (hence not requiring quotes),
while making putid() treat any non-ASCII as requiring quoting.
We could remove the resulting excess quoting once we feel that
no unpatched servers remain in the wild, but that'll be years.

A lesser problem is that getid() did the wrong thing with an input
consisting of just two double quotes ("").  That has to represent an
empty string, but getid() read it as a single double quote instead.
The case cannot arise in the normal course of events, since we don't
allow empty-string role names.  But let's fix it while we're here.

Although we've not heard field reports of problems with non-ASCII
role names, there's clearly a hazard there, so back-patch to all
supported versions.

Reported-by: Peter Eisentraut <peter@eisentraut.org>
Author: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: https://postgr.es/m/3792884.1751492172@sss.pgh.pa.us
Backpatch-through: 13

src/backend/utils/adt/acl.c

@@ -130,6 +130,22 @@ static AclResult pg_role_aclcheck(Oid role_oid, Oid roleid, AclMode mode);
 static void RoleMembershipCacheCallback(Datum arg, int cacheid, uint32 hashvalue);
 
 
+/*
+ * Test whether an identifier char can be left unquoted in ACLs.
+ *
+ * Formerly, we used isalnum() even on non-ASCII characters, resulting in
+ * unportable behavior.  To ensure dump compatibility with old versions,
+ * we now treat high-bit-set characters as always requiring quoting during
+ * putid(), but getid() will always accept them without quotes.
+ */
+static inline bool
+is_safe_acl_char(unsigned char c, bool is_getid)
+{
+	if (IS_HIGHBIT_SET(c))
+		return is_getid;
+	return isalnum(c) || c == '_';
+}
+
 /*
  * getid
  *		Consumes the first alphanumeric string (identifier) found in string
@@ -155,21 +171,22 @@ getid(const char *s, char *n, Node *escontext)
 
 	while (isspace((unsigned char) *s))
 		s++;
-	/* This code had better match what putid() does, below */
 	for (;
 		 *s != '\0' &&
-		 (isalnum((unsigned char) *s) ||
+		 (in_quotes || *s == '"' || is_safe_acl_char(*s, true));
-		  *s == '_' ||
-		  *s == '"' ||
-		  in_quotes);
 		 s++)
 	{
 		if (*s == '"')
 		{
+			if (!in_quotes)
+			{
+				in_quotes = true;
+				continue;
+			}
 			/* safe to look at next char (could be '\0' though) */
 			if (*(s + 1) != '"')
 			{
-				in_quotes = !in_quotes;
+				in_quotes = false;
 				continue;
 			}
 			/* it's an escaped double quote; skip the escaping char */
@@ -203,10 +220,10 @@ putid(char *p, const char *s)
 	const char *src;
 	bool		safe = true;
 
+	/* Detect whether we need to use double quotes */
 	for (src = s; *src; src++)
 	{
-		/* This test had better match what getid() does, above */
+		if (!is_safe_acl_char(*src, false))
-		if (!isalnum((unsigned char) *src) && *src != '_')
 		{
 			safe = false;
 			break;

src/test/regress/expected/privileges.out

@@ -2332,6 +2332,26 @@ SELECT makeaclitem('regress_priv_user1'::regrole, 'regress_priv_user2'::regrole,
 SELECT makeaclitem('regress_priv_user1'::regrole, 'regress_priv_user2'::regrole,
 	'SELECT, fake_privilege', FALSE);  -- error
 ERROR:  unrecognized privilege type: "fake_privilege"
+-- Test quoting and dequoting of user names in ACLs
+CREATE ROLE "regress_""quoted";
+SELECT makeaclitem('regress_"quoted'::regrole, 'regress_"quoted'::regrole,
+                   'SELECT', TRUE);
+               makeaclitem                
+------------------------------------------
+ "regress_""quoted"=r*/"regress_""quoted"
+(1 row)
+
+SELECT '"regress_""quoted"=r*/"regress_""quoted"'::aclitem;
+                 aclitem                  
+------------------------------------------
+ "regress_""quoted"=r*/"regress_""quoted"
+(1 row)
+
+SELECT '""=r*/""'::aclitem;  -- used to be misparsed as """"
+ERROR:  a name must follow the "/" sign
+LINE 1: SELECT '""=r*/""'::aclitem;
+               ^
+DROP ROLE "regress_""quoted";
 -- Test non-throwing aclitem I/O
 SELECT pg_input_is_valid('regress_priv_user1=r/regress_priv_user2', 'aclitem');
  pg_input_is_valid 

src/test/regress/sql/privileges.sql

@@ -1481,6 +1481,14 @@ SELECT makeaclitem('regress_priv_user1'::regrole, 'regress_priv_user2'::regrole,
 SELECT makeaclitem('regress_priv_user1'::regrole, 'regress_priv_user2'::regrole,
 	'SELECT, fake_privilege', FALSE);  -- error
 
+-- Test quoting and dequoting of user names in ACLs
+CREATE ROLE "regress_""quoted";
+SELECT makeaclitem('regress_"quoted'::regrole, 'regress_"quoted'::regrole,
+                   'SELECT', TRUE);
+SELECT '"regress_""quoted"=r*/"regress_""quoted"'::aclitem;
+SELECT '""=r*/""'::aclitem;  -- used to be misparsed as """"
+DROP ROLE "regress_""quoted";
+
 -- Test non-throwing aclitem I/O
 SELECT pg_input_is_valid('regress_priv_user1=r/regress_priv_user2', 'aclitem');
 SELECT pg_input_is_valid('regress_priv_user1=r/', 'aclitem');