Support host names in pg_hba.conf

Peter Eisentraut, reviewed by KaiGai Kohei and Tom Lane

doc/src/sgml/client-auth.sgml

@@ -80,9 +80,9 @@
    A record is made
    up of a number of fields which are separated by spaces and/or tabs.
    Fields can contain white space if the field value is quoted.
-   Quoting one of the keywords in a database or user name field (e.g.,
+   Quoting one of the keywords in a database, user, or address field (e.g.,
    <literal>all</> or <literal>replication</>) makes the word lose its special
-   character, and just match a database or user with that name.
+   character, and just match a database, user, or host with that name.
   </para>
 
   <para>
@@ -101,9 +101,9 @@
    A record can have one of the seven formats
 <synopsis>
 local      <replaceable>database</replaceable>  <replaceable>user</replaceable>  <replaceable>auth-method</replaceable>  <optional><replaceable>auth-options</replaceable></optional>
-host       <replaceable>database</replaceable>  <replaceable>user</replaceable>  <replaceable>CIDR-address</replaceable>  <replaceable>auth-method</replaceable>  <optional><replaceable>auth-options</replaceable></optional>
-hostssl    <replaceable>database</replaceable>  <replaceable>user</replaceable>  <replaceable>CIDR-address</replaceable>  <replaceable>auth-method</replaceable>  <optional><replaceable>auth-options</replaceable></optional>
-hostnossl  <replaceable>database</replaceable>  <replaceable>user</replaceable>  <replaceable>CIDR-address</replaceable>  <replaceable>auth-method</replaceable>  <optional><replaceable>auth-options</replaceable></optional>
+host       <replaceable>database</replaceable>  <replaceable>user</replaceable>  <replaceable>address</replaceable>  <replaceable>auth-method</replaceable>  <optional><replaceable>auth-options</replaceable></optional>
+hostssl    <replaceable>database</replaceable>  <replaceable>user</replaceable>  <replaceable>address</replaceable>  <replaceable>auth-method</replaceable>  <optional><replaceable>auth-options</replaceable></optional>
+hostnossl  <replaceable>database</replaceable>  <replaceable>user</replaceable>  <replaceable>address</replaceable>  <replaceable>auth-method</replaceable>  <optional><replaceable>auth-options</replaceable></optional>
 host       <replaceable>database</replaceable>  <replaceable>user</replaceable>  <replaceable>IP-address</replaceable>  <replaceable>IP-mask</replaceable>  <replaceable>auth-method</replaceable>  <optional><replaceable>auth-options</replaceable></optional>
 hostssl    <replaceable>database</replaceable>  <replaceable>user</replaceable>  <replaceable>IP-address</replaceable>  <replaceable>IP-mask</replaceable>  <replaceable>auth-method</replaceable>  <optional><replaceable>auth-options</replaceable></optional>
 hostnossl  <replaceable>database</replaceable>  <replaceable>user</replaceable>  <replaceable>IP-address</replaceable>  <replaceable>IP-mask</replaceable>  <replaceable>auth-method</replaceable>  <optional><replaceable>auth-options</replaceable></optional>
@@ -218,13 +218,17 @@ hostnossl  <replaceable>database</replaceable>  <replaceable>user</replaceable>
     </varlistentry>
 
     <varlistentry>
-     <term><replaceable>CIDR-address</replaceable></term>
+     <term><replaceable>address</replaceable></term>
      <listitem>
       <para>
-       Specifies the client machine IP address range that this record
-       matches. This field contains an IP address in standard dotted decimal
-       notation and a <acronym>CIDR</> mask length. (IP addresses can only be
-       specified numerically, not as domain or host names.)  The mask
+       Specifies the client machine addresses that this record
+       matches.  This field can contain either a host name, an IP
+       address range, or one of the special key words mentioned below.
+      </para>
+
+      <para>
+       An IP address is specified in standard dotted decimal
+       notation with a <acronym>CIDR</> mask length.  The mask
        length indicates the number of high-order bits of the client
        IP address that must match.  Bits to the right of this must
        be zero in the given IP address.
@@ -233,14 +237,7 @@ hostnossl  <replaceable>database</replaceable>  <replaceable>user</replaceable>
       </para>
 
       <para>
-       Instead of a <replaceable>CIDR-address</replaceable>, you can write
-       <literal>samehost</literal> to match any of the server's own IP
-       addresses, or <literal>samenet</literal> to match any address in any
-       subnet that the server is directly connected to.
-      </para>
-
-      <para>
-       Typical examples of a <replaceable>CIDR-address</replaceable> are
+       Typical examples of an IP address range specified this way are
        <literal>172.20.143.89/32</literal> for a single host, or
        <literal>172.20.143.0/24</literal> for a small network, or
        <literal>10.6.0.0/16</literal> for a larger one.
@@ -259,6 +256,67 @@ hostnossl  <replaceable>database</replaceable>  <replaceable>user</replaceable>
        support for IPv6 addresses.
       </para>
 
+      <para>
+       You can also write
+       <literal>samehost</literal> to match any of the server's own IP
+       addresses, or <literal>samenet</literal> to match any address in any
+       subnet that the server is directly connected to.
+      </para>
+
+      <para>
+       If a host name is specified (anything that is not an IP address
+       or a special key word is processed as a potential host name),
+       that name is compared with the result of a reverse name
+       resolution of the client's IP address (e.g., reverse DNS
+       lookup, if DNS is used).  Host name comparisons are case
+       insensitive.  If there is a match, then a forward name
+       resolution (e.g., forward DNS lookup) is performed on the host
+       name to check whether any of the addresses it resolves to are
+       equal to the client's IP address.  If both directions match,
+       then the entry is considered to match.  (The host name that is
+       used in <filename>pg_hba.conf</filename> should be the one that
+       address-to-name resolution of the client's IP address returns,
+       otherwise the line won't be matched.  Some host name databases
+       allow associating an IP address with multiple host names, but
+       the operating system will only return one host name when asked
+       to resolve an IP address.)
+      </para>
+
+      <para>
+       When host names are specified
+       in <filename>pg_hba.conf</filename>, you should make sure that
+       name resolution is reasonably fast.  It can be of advantage to
+       set up a local name resolution cache such
+       as <command>nscd</command>.  Also, you may wish to enable the
+       configuration parameter <varname>log_hostname</varname> to see
+       the client's host name instead of the IP address in the log.
+      </para>
+
+      <sidebar>
+       <para>
+        Occasionally, users have wondered why host names are handled
+        in this seemingly complicated way with two name resolutions
+        and requiring reverse lookup of IP addresses, which is
+        sometimes not set up or points to some undesirable host name.
+        It is primarily for efficiency: A connection attempt requires
+        two resolver lookups of the current client's address.  If
+        there is resolver problem with that address, it becomes only
+        that client's problem.  A hypothetical alternative
+        implementation which only does forward lookups would have to
+        resolve every host name mentioned in
+        <filename>pg_hba.conf</filename> at every connection attempt.
+        That would already be slow by itself.  And if there is a
+        resolver problem with one of the host names, it becomes
+        everyone's problem.
+       </para>
+
+       <para>
+        Note that this behavior is consistent with other popular
+        implementations of host name-based access control, such as the
+        Apache HTTP Server and TCP Wrappers.
+       </para>
+      </sidebar>
+
       <para>
        This field only applies to <literal>host</literal>,
        <literal>hostssl</literal>, and <literal>hostnossl</> records.
@@ -511,12 +569,12 @@ hostnossl  <replaceable>database</replaceable>  <replaceable>user</replaceable>
 # any database user name using Unix-domain sockets (the default for local
 # connections).
 #
-# TYPE  DATABASE        USER            CIDR-ADDRESS            METHOD
+# TYPE  DATABASE        USER            ADDRESS                 METHOD
 local   all             all                                     trust
 
 # The same using local loopback TCP/IP connections.
 #
-# TYPE  DATABASE        USER            CIDR-ADDRESS            METHOD
+# TYPE  DATABASE        USER            ADDRESS                 METHOD
 host    all             all             127.0.0.1/32            trust
 
 # The same as the previous line, but using a separate netmask column
@@ -524,17 +582,27 @@ host    all             all             127.0.0.1/32            trust
 # TYPE  DATABASE        USER            IP-ADDRESS      IP-MASK             METHOD
 host    all             all             127.0.0.1       255.255.255.255     trust
 
+# The same over IPv6.
+#
+# TYPE  DATABASE        USER            ADDRESS                 METHOD
+host    all             all             ::1/128                 trust
+
+# The same using a host name (would typically cover both IPv4 and IPv6).
+#
+# TYPE  DATABASE        USER            ADDRESS                 METHOD
+host    all             all             localhost               trust
+
 # Allow any user from any host with IP address 192.168.93.x to connect
 # to database "postgres" as the same user name that ident reports for
 # the connection (typically the operating system user name).
 #
-# TYPE  DATABASE        USER            CIDR-ADDRESS            METHOD
+# TYPE  DATABASE        USER            ADDRESS                 METHOD
 host    postgres        all             192.168.93.0/24         ident
 
 # Allow any user from host 192.168.12.10 to connect to database
 # "postgres" if the user's password is correctly supplied.
 #
-# TYPE  DATABASE        USER            CIDR-ADDRESS            METHOD
+# TYPE  DATABASE        USER            ADDRESS                 METHOD
 host    postgres        all             192.168.12.10/32        md5
 
 # In the absence of preceding "host" lines, these two lines will
@@ -543,7 +611,7 @@ host    postgres        all             192.168.12.10/32        md5
 # on the Internet.  The zero mask causes no bits of the host IP
 # address to be considered, so it matches any host.
 #
-# TYPE  DATABASE        USER            CIDR-ADDRESS            METHOD
+# TYPE  DATABASE        USER            ADDRESS                 METHOD
 host    all             all             192.168.54.1/32         reject
 host    all             all             0.0.0.0/0               krb5
 
@@ -553,7 +621,7 @@ host    all             all             0.0.0.0/0               krb5
 # connection is allowed if there is an entry in pg_ident.conf for map
 # "omicron" that says "bryanh" is allowed to connect as "guest1".
 #
-# TYPE  DATABASE        USER            CIDR-ADDRESS            METHOD
+# TYPE  DATABASE        USER            ADDRESS                 METHOD
 host    all             all             192.168.0.0/16          ident map=omicron
 
 # If these are the only three lines for local connections, they will
@@ -563,7 +631,7 @@ host    all             all             192.168.0.0/16          ident map=omicro
 # $PGDATA/admins contains a list of names of administrators.  Passwords
 # are required in all cases.
 #
-# TYPE  DATABASE        USER            CIDR-ADDRESS            METHOD
+# TYPE  DATABASE        USER            ADDRESS                 METHOD
 local   sameuser        all                                     md5
 local   all             @admins                                 md5
 local   all             +support                                md5

src/backend/libpq/hba.c

@@ -102,8 +102,8 @@ pg_isblank(const char c)
  * whichever comes first. If no more tokens on line, position the file to the
  * beginning of the next line or EOF, whichever comes first.
  *
- * Handle comments. Treat unquoted keywords that might be role names or
- * database names specially, by appending a newline to them.  Also, when
+ * Handle comments. Treat unquoted keywords that might be role, database, or
+ * host names specially, by appending a newline to them.  Also, when
  * a token is terminated by a comma, the comma is included in the returned
  * token.
  */
@@ -198,6 +198,8 @@ next_token(FILE *fp, char *buf, int bufsz, bool *initial_quote)
 
 	if (!saw_quote &&
 		(strcmp(start_buf, "all") == 0 ||
+		 strcmp(start_buf, "samehost") == 0 ||
+		 strcmp(start_buf, "samenet") == 0 ||
 		 strcmp(start_buf, "sameuser") == 0 ||
 		 strcmp(start_buf, "samegroup") == 0 ||
 		 strcmp(start_buf, "samerole") == 0 ||
@@ -540,6 +542,102 @@ check_db(const char *dbname, const char *role, Oid roleid, char *param_str)
 	return false;
 }
 
+static bool
+ipv4eq(struct sockaddr_in *a, struct sockaddr_in *b)
+{
+	return (a->sin_addr.s_addr == b->sin_addr.s_addr);
+}
+
+static bool
+ipv6eq(struct sockaddr_in6 *a, struct sockaddr_in6 *b)
+{
+	int i;
+
+	for (i = 0; i < 16; i++)
+		if (a->sin6_addr.s6_addr[i] != b->sin6_addr.s6_addr[i])
+			return false;
+
+	return true;
+}
+
+/*
+ * Check to see if a connecting IP matches a given host name.
+ */
+static bool
+check_hostname(hbaPort *port, const char *hostname)
+{
+	struct addrinfo *gai_result, *gai;
+	int			ret;
+	bool		found;
+
+	/* Lookup remote host name if not already done */
+	if (!port->remote_hostname)
+	{
+		char		remote_hostname[NI_MAXHOST];
+
+		if (pg_getnameinfo_all(&port->raddr.addr, port->raddr.salen,
+							   remote_hostname, sizeof(remote_hostname),
+							   NULL, 0,
+							   0))
+			return false;
+
+		port->remote_hostname = pstrdup(remote_hostname);
+	}
+
+	if (pg_strcasecmp(port->remote_hostname, hostname) != 0)
+		return false;
+
+	/* Lookup IP from host name and check against original IP */
+
+	if (port->remote_hostname_resolv == +1)
+		return true;
+	if (port->remote_hostname_resolv == -1)
+		return false;
+
+	ret = getaddrinfo(port->remote_hostname, NULL, NULL, &gai_result);
+	if (ret != 0)
+		ereport(ERROR,
+				(errmsg("could not translate host name \"%s\" to address: %s",
+						port->remote_hostname, gai_strerror(ret))));
+
+	found = false;
+	for (gai = gai_result; gai; gai = gai->ai_next)
+	{
+		if (gai->ai_addr->sa_family == port->raddr.addr.ss_family)
+		{
+			if (gai->ai_addr->sa_family == AF_INET)
+			{
+				if (ipv4eq((struct sockaddr_in *) gai->ai_addr,
+						   (struct sockaddr_in *) &port->raddr.addr))
+				{
+					found = true;
+					break;
+				}
+			}
+			else if (gai->ai_addr->sa_family == AF_INET6)
+			{
+				if (ipv6eq((struct sockaddr_in6 *) gai->ai_addr,
+						   (struct sockaddr_in6 *) &port->raddr.addr))
+				{
+					found = true;
+					break;
+				}
+			}
+		}
+	}
+
+	if (gai_result)
+		freeaddrinfo(gai_result);
+
+	if (!found)
+		elog(DEBUG2, "pg_hba.conf host name \"%s\" rejected because address resolution did not return a match with IP address of client",
+			 hostname);
+
+	port->remote_hostname_resolv = found ? +1 : -1;
+
+	return found;
+}
+
 /*
  * Check to see if a connecting IP matches the given address and netmask.
  */
@@ -782,12 +880,12 @@ parse_hba_line(List *line, int line_num, HbaLine *parsedline)
 		token = lfirst(line_item);
 
 		/* Is it equal to 'samehost' or 'samenet'? */
-		if (strcmp(token, "samehost") == 0)
+		if (strcmp(token, "samehost\n") == 0)
 		{
 			/* Any IP on this host is allowed to connect */
 			parsedline->ip_cmp_method = ipCmpSameHost;
 		}
-		else if (strcmp(token, "samenet") == 0)
+		else if (strcmp(token, "samenet\n") == 0)
 		{
 			/* Any IP on the host's subnets is allowed to connect */
 			parsedline->ip_cmp_method = ipCmpSameNet;
@@ -816,7 +914,12 @@ parse_hba_line(List *line, int line_num, HbaLine *parsedline)
 			hints.ai_next = NULL;
 
 			ret = pg_getaddrinfo_all(token, NULL, &hints, &gai_result);
-			if (ret || !gai_result)
+			if (ret == 0 && gai_result)
+				memcpy(&parsedline->addr, gai_result->ai_addr,
+					   gai_result->ai_addrlen);
+			else if (ret == EAI_NONAME)
+				parsedline->hostname = token;
+			else
 			{
 				ereport(LOG,
 						(errcode(ERRCODE_CONFIG_FILE_ERROR),
@@ -830,13 +933,24 @@ parse_hba_line(List *line, int line_num, HbaLine *parsedline)
 				return false;
 			}
 
-			memcpy(&parsedline->addr, gai_result->ai_addr,
-				   gai_result->ai_addrlen);
 			pg_freeaddrinfo_all(hints.ai_family, gai_result);
 
 			/* Get the netmask */
 			if (cidr_slash)
 			{
+				if (parsedline->hostname)
+				{
+					*cidr_slash = '/';	/* restore token for message */
+					ereport(LOG,
+							(errcode(ERRCODE_CONFIG_FILE_ERROR),
+							 errmsg("specifying both host name and CIDR mask is invalid: \"%s\"",
+									token),
+							 errcontext("line %d of configuration file \"%s\"",
+										line_num, HbaFileName)));
+					pfree(token);
+					return false;
+				}
+
 				if (pg_sockaddr_cidr_mask(&parsedline->mask, cidr_slash + 1,
 										  parsedline->addr.ss_family) < 0)
 				{
@@ -852,7 +966,7 @@ parse_hba_line(List *line, int line_num, HbaLine *parsedline)
 				}
 				pfree(token);
 			}
-			else
+			else if (!parsedline->hostname)
 			{
 				/* Read the mask field. */
 				pfree(token);
@@ -1369,10 +1483,19 @@ check_hba(hbaPort *port)
 			switch (hba->ip_cmp_method)
 			{
 				case ipCmpMask:
-					if (!check_ip(&port->raddr,
-								  (struct sockaddr *) & hba->addr,
-								  (struct sockaddr *) & hba->mask))
-						continue;
+					if (hba->hostname)
+					{
+						if (!check_hostname(port,
+											hba->hostname))
+							continue;
+					}
+					else
+					{
+						if (!check_ip(&port->raddr,
+									  (struct sockaddr *) & hba->addr,
+									  (struct sockaddr *) & hba->mask))
+							continue;
+					}
 					break;
 				case ipCmpSameHost:
 				case ipCmpSameNet:

src/backend/libpq/pg_hba.conf.sample

@@ -10,9 +10,9 @@
 # databases they can access.  Records take one of these forms:
 #
 # local      DATABASE  USER  METHOD  [OPTIONS]
-# host       DATABASE  USER  CIDR-ADDRESS  METHOD  [OPTIONS]
-# hostssl    DATABASE  USER  CIDR-ADDRESS  METHOD  [OPTIONS]
-# hostnossl  DATABASE  USER  CIDR-ADDRESS  METHOD  [OPTIONS]
+# host       DATABASE  USER  ADDRESS  METHOD  [OPTIONS]
+# hostssl    DATABASE  USER  ADDRESS  METHOD  [OPTIONS]
+# hostnossl  DATABASE  USER  ADDRESS  METHOD  [OPTIONS]
 #
 # (The uppercase items must be replaced by actual values.)
 #
@@ -29,14 +29,15 @@
 # you can also write a file name prefixed with "@" to include names
 # from a separate file.
 #
-# CIDR-ADDRESS specifies the set of hosts the record matches.  It is
-# made up of an IP address and a CIDR mask that is an integer (between
-# 0 and 32 (IPv4) or 128 (IPv6) inclusive) that specifies the number
-# of significant bits in the mask.  Alternatively, you can write an IP
-# address and netmask in separate columns to specify the set of hosts.
-# Instead of a CIDR-address, you can write "samehost" to match any of
-# the server's own IP addresses, or "samenet" to match any address in
-# any subnet that the server is directly connected to.
+# ADDRESS specifies the set of hosts the record matches.  It can be a
+# host name, or it is made up of an IP address and a CIDR mask that is
+# an integer (between 0 and 32 (IPv4) or 128 (IPv6) inclusive) that
+# specifies the number of significant bits in the mask.
+# Alternatively, you can write an IP address and netmask in separate
+# columns to specify the set of hosts.  Instead of a CIDR-address, you
+# can write "samehost" to match any of the server's own IP addresses,
+# or "samenet" to match any address in any subnet that the server is
+# directly connected to.
 #
 # METHOD can be "trust", "reject", "md5", "password", "gss", "sspi",
 # "krb5", "ident", "pam", "ldap", "radius" or "cert".  Note that
@@ -70,7 +71,7 @@
 
 @authcomment@
 
-# TYPE  DATABASE        USER            CIDR-ADDRESS            METHOD
+# TYPE  DATABASE        USER            ADDRESS                 METHOD
 
 @remove-line-for-nolocal@# "local" is for Unix domain socket connections only
 @remove-line-for-nolocal@local   all             all                                     @authmethod@

src/backend/postmaster/postmaster.c

@@ -3422,6 +3422,8 @@ BackendInitialize(Port *port)
 	 */
 	port->remote_host = strdup(remote_host);
 	port->remote_port = strdup(remote_port);
+	if (log_hostname)
+		port->remote_hostname = port->remote_host;
 
 	/*
 	 * Ready to begin client interaction.  We will give up and exit(1) after a

src/include/libpq/hba.h

@@ -56,6 +56,7 @@ typedef struct
 	struct sockaddr_storage addr;
 	struct sockaddr_storage mask;
 	IPCompareMethod ip_cmp_method;
+	char	   *hostname;
 	UserAuth	auth_method;
 
 	char	   *usermap;

src/include/libpq/libpq-be.h

@@ -109,6 +109,10 @@ typedef struct Port
 	SockAddr	laddr;			/* local addr (postmaster) */
 	SockAddr	raddr;			/* remote addr (client) */
 	char	   *remote_host;	/* name (or ip addr) of remote host */
+	char	   *remote_hostname; /* name (not ip addr) of remote host, if available */
+	int			remote_hostname_resolv; /* +1 = remote_hostname is known to resolve to client's IP address;
+										   -1 = remote_hostname is known NOT to resolve to client's IP address;
+										   0 = we have not done the forward DNS lookup yet */
 	char	   *remote_port;	/* text rep of remote port */
 	CAC_state	canAcceptConnections;	/* postmaster connection status */