Date: Fri, 1 Apr 2022 15:06:48 -0700
From: Nathan Bossart <nathandbossart@gmail.com>
To: pgsql-hackers@postgresql.org
Subject: use has_privs_of_role() for pg_hba.conf
Message-ID: <20220401220648.GA615994@nathanxps13>
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Hi hackers,

6198420 ensured that has_privs_of_role() is used for predefined roles,
which means that the role inheritance hierarchy is checked instead of mere
role membership.  However, inheritance is still not respected for
pg_hba.conf.  Specifically, "samerole", "samegroup", and "+" still use
is_member_of_role_nosuper().

The attached patch introduces has_privs_of_role_nosuper() and uses it for
the aforementioned pg_hba.conf functionality.  I think this is desirable
for consistency.  If a role_a has membership in role_b but none of its
privileges (i.e., NOINHERIT), does it make sense that role_a should match
+role_b in pg_hba.conf?  It is true that role_a could always "SET ROLE
role_b", and with this change, the user won't even have the ability to log
in to run SET ROLE.  But I'm not sure if that's a strong enough argument
for deviating from the standard role privilege checks.

Thoughts?

-- 
Nathan Bossart
Amazon Web Services: https://aws.amazon.com

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From 5c1a5aaaff949fc25afaa6856ca2a85a54c8efdc Mon Sep 17 00:00:00 2001
From: Nathan Bossart <nathandbossart@gmail.com>
Date: Fri, 1 Apr 2022 11:40:51 -0700
Subject: [PATCH v1 1/1] Use has_privs_of_role for samerole, samegroup, and +
 in pg_hba.conf.

6198420 ensured that has_privs_of_role() is used for predefined
roles, which means that the role privilege inheritance hierarchy is
checked instead of mere role membership.  However, inheritance is
still not respected for pg_hba.conf.  This change alters the
authentication logic to consider role privileges instead of just
role membership.

Do not back-patch.

Author: Nathan Bossart
---
 doc/src/sgml/client-auth.sgml | 18 +++++++++---------
 src/backend/libpq/hba.c       | 19 ++++++++++---------
 src/backend/utils/adt/acl.c   | 23 +++++++++++++++++++++++
 src/include/utils/acl.h       |  1 +
 4 files changed, 43 insertions(+), 18 deletions(-)

diff --git a/doc/src/sgml/client-auth.sgml b/doc/src/sgml/client-auth.sgml
index 142b0affcb..5c63842e52 100644
--- a/doc/src/sgml/client-auth.sgml
+++ b/doc/src/sgml/client-auth.sgml
@@ -221,12 +221,12 @@ hostnogssenc  <replaceable>database</replaceable>  <replaceable>user</replaceabl
        The value <literal>sameuser</literal> specifies that the record
        matches if the requested database has the same name as the
        requested user.  The value <literal>samerole</literal> specifies that
-       the requested user must be a member of the role with the same
+       the requested user must have privileges of the role with the same
        name as the requested database.  (<literal>samegroup</literal> is an
        obsolete but still accepted spelling of <literal>samerole</literal>.)
-       Superusers are not considered to be members of a role for the
-       purposes of <literal>samerole</literal> unless they are explicitly
-       members of the role, directly or indirectly, and not just by
+       Superusers are not considered to have privileges of a role for the
+       purposes of <literal>samerole</literal> unless they explicitly have
+       privileges of the role, directly or indirectly, and not just by
        virtue of being a superuser.
        The value <literal>replication</literal> specifies that the record
        matches if a physical replication connection is requested, however, it
@@ -252,10 +252,10 @@ hostnogssenc  <replaceable>database</replaceable>  <replaceable>user</replaceabl
        database user, or a group name preceded by <literal>+</literal>.
        (Recall that there is no real distinction between users and groups
        in <productname>PostgreSQL</productname>; a <literal>+</literal> mark really means
-       <quote>match any of the roles that are directly or indirectly members
+       <quote>match any of the roles that directly or indirectly have privileges
        of this role</quote>, while a name without a <literal>+</literal> mark matches
        only that specific role.) For this purpose, a superuser is only
-       considered to be a member of a role if they are explicitly a member
+       considered to have privileges of a role if they explicitly have privileges
        of the role, directly or indirectly, and not just by virtue of
        being a superuser.
        Multiple user names can be supplied by separating them with commas.
@@ -788,9 +788,9 @@ host    all             all             192.168.0.0/16          ident map=omicro
 # If these are the only three lines for local connections, they will
 # allow local users to connect only to their own databases (databases
 # with the same name as their database user name) except for administrators
-# and members of role "support", who can connect to all databases.  The file
-# $PGDATA/admins contains a list of names of administrators.  Passwords
-# are required in all cases.
+# and roles with privileges of role "support", who can connect to all
+# databases.  The file $PGDATA/admins contains a list of names of
+# administrators.  Passwords are required in all cases.
 #
 # TYPE  DATABASE        USER            ADDRESS                 METHOD
 local   sameuser        all                                     md5
diff --git a/src/backend/libpq/hba.c b/src/backend/libpq/hba.c
index f8393ca8ed..247118fa30 100644
--- a/src/backend/libpq/hba.c
+++ b/src/backend/libpq/hba.c
@@ -546,13 +546,13 @@ tokenize_auth_file(const char *filename, FILE *file, List **tok_lines,
 
 
 /*
- * Does user belong to role?
+ * Does user have privileges of role?
  *
  * userid is the OID of the role given as the attempted login identifier.
- * We check to see if it is a member of the specified role name.
+ * We check to see if it has privileges of the specified role name.
  */
 static bool
-is_member(Oid userid, const char *role)
+has_privs(Oid userid, const char *role)
 {
 	Oid			roleid;
 
@@ -565,11 +565,12 @@ is_member(Oid userid, const char *role)
 		return false;			/* if target role not exist, say "no" */
 
 	/*
-	 * See if user is directly or indirectly a member of role. For this
-	 * purpose, a superuser is not considered to be automatically a member of
-	 * the role, so group auth only applies to explicit membership.
+	 * See if user directly or indirectly has privileges of role. For this
+	 * purpose, a superuser is not considered to automatically have
+	 * privileges of the role, so group auth only applies to explicit
+	 * privileges.
 	 */
-	return is_member_of_role_nosuper(userid, roleid);
+	return has_privs_of_role_nosuper(userid, roleid);
 }
 
 /*
@@ -586,7 +587,7 @@ check_role(const char *role, Oid roleid, List *tokens)
 		tok = lfirst(cell);
 		if (!tok->quoted && tok->string[0] == '+')
 		{
-			if (is_member(roleid, tok->string + 1))
+			if (has_privs(roleid, tok->string + 1))
 				return true;
 		}
 		else if (token_matches(tok, role) ||
@@ -627,7 +628,7 @@ check_db(const char *dbname, const char *role, Oid roleid, List *tokens)
 		else if (token_is_keyword(tok, "samegroup") ||
 				 token_is_keyword(tok, "samerole"))
 		{
-			if (is_member(roleid, dbname))
+			if (has_privs(roleid, dbname))
 				return true;
 		}
 		else if (token_is_keyword(tok, "replication"))
diff --git a/src/backend/utils/adt/acl.c b/src/backend/utils/adt/acl.c
index 83cf7ac9ff..061fa171fc 100644
--- a/src/backend/utils/adt/acl.c
+++ b/src/backend/utils/adt/acl.c
@@ -4855,6 +4855,29 @@ has_privs_of_role(Oid member, Oid role)
 }
 
 
+/*
+ * Does member have the privileges of role, not considering superuserness?
+ *
+ * This is identical to has_privs_of_role except we ignore superuser
+ * status.
+ */
+bool
+has_privs_of_role_nosuper(Oid member, Oid role)
+{
+	/* Fast path for simple case */
+	if (member == role)
+		return true;
+
+	/*
+	 * Find all the roles that member has the privileges of, including
+	 * multi-level recursion, then see if target role is any one of them.
+	 */
+	return list_member_oid(roles_is_member_of(member, ROLERECURSE_PRIVS,
+											  InvalidOid, NULL),
+						   role);
+}
+
+
 /*
  * Is member a member of role (directly or indirectly)?
  *
diff --git a/src/include/utils/acl.h b/src/include/utils/acl.h
index 91ce3d8e9c..bf9f22124e 100644
--- a/src/include/utils/acl.h
+++ b/src/include/utils/acl.h
@@ -208,6 +208,7 @@ extern AclMode aclmask(const Acl *acl, Oid roleid, Oid ownerId,
 extern int	aclmembers(const Acl *acl, Oid **roleids);
 
 extern bool has_privs_of_role(Oid member, Oid role);
+extern bool has_privs_of_role_nosuper(Oid member, Oid role);
 extern bool is_member_of_role(Oid member, Oid role);
 extern bool is_member_of_role_nosuper(Oid member, Oid role);
 extern bool is_admin_of_role(Oid member, Oid role);
-- 
2.25.1


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