Add realhostname() - a function to correctly lookup

a name by address and ensure that the name resolves
back to the original address.

4 files changed, 190 insertions, 3 deletions

diff --git a/lib/libutil/Makefile b/lib/libutil/Makefile
index 7754e6e..9e9d04b 100644
--- a/lib/libutil/Makefile
+++ b/lib/libutil/Makefile
@@ -7,10 +7,10 @@ CFLAGS+=-Wall -DLIBC_SCCS -I${.CURDIR} -I${.CURDIR}/../../sys
 #CFLAGS+=LOGIN_CAP_AUTH
 SRCS=	login.c login_tty.c logout.c logwtmp.c pty.c setproctitle.c \
 	login_cap.c login_class.c login_auth.c login_times.c login_ok.c \
-	_secure_path.c uucplock.c property.c auth.c
+	_secure_path.c uucplock.c property.c auth.c realhostname.c
 MAN3+=	login.3 login_auth.3 login_tty.3 logout.3 logwtmp.3 pty.3 \
 	setproctitle.3 login_cap.3 login_class.3 login_times.3 login_ok.3 \
-	_secure_path.3 uucplock.3 property.3 auth.3
+	_secure_path.3 uucplock.3 property.3 auth.3 realhostname.3
 MAN5+=	login.conf.5 auth.conf.5
 MLINKS+= property.3 properties_read.3  property.3 properties_free.3
 MLINKS+= property.3 property_find.3
diff --git a/lib/libutil/libutil.h b/lib/libutil/libutil.h
index dda01c1..32957d9 100644
--- a/lib/libutil/libutil.h
+++ b/lib/libutil/libutil.h
@@ -18,7 +18,7 @@
  * 5. Modifications may be freely made to this file providing the above
  *    conditions are met.
  *
- * $Id: libutil.h,v 1.20 1998/10/09 07:32:38 jkh Exp $
+ * $Id: libutil.h,v 1.21 1998/12/16 17:52:15 bde Exp $
  */
 
 #ifndef _LIBUTIL_H_
@@ -37,6 +37,7 @@ typedef struct _property {
 struct termios;
 struct winsize;
 struct utmp;
+struct in_addr;
 
 __BEGIN_DECLS
 void	setproctitle __P((const char *_fmt, ...)) __printf0like(1, 2);
@@ -58,6 +59,7 @@ properties properties_read __P((int fd));
 void	properties_free __P((properties list));
 char	*property_find __P((properties list, const char *name));
 char	*auth_getval __P((const char *name));
+int	realhostname __P((char *host, size_t hsize, const struct in_addr *ip));
 __END_DECLS
 
 #define UU_LOCK_INUSE (1)
@@ -70,4 +72,10 @@ __END_DECLS
 #define UU_LOCK_TRY_ERR (-6)
 #define UU_LOCK_OWNER_ERR (-7)
 
+/* return values from realhostname() */
+#define HOSTNAME_FOUND		(0)
+#define HOSTNAME_INCORRECTNAME	(1)
+#define HOSTNAME_INVALIDADDR	(2)
+#define HOSTNAME_INVALIDNAME	(3)
+
 #endif /* !_LIBUTIL_H_ */
diff --git a/lib/libutil/realhostname.3 b/lib/libutil/realhostname.3
new file mode 100644
index 0000000..4298e7f
--- /dev/null
+++ b/lib/libutil/realhostname.3
@@ -0,0 +1,106 @@
+.\" Copyright (c) 1999 Brian Somers <brian@Awfulhak.org>
+.\" All rights reserved.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.\"	$Id:$
+.\"
+.Dd April 6, 1999
+.Os
+.Dt REALHOSTNAME 3
+.Sh NAME
+.Nm realhostname
+.Nd "convert an IP number to the real host name"
+.Sh SYNOPSIS
+.Fd #include <sys/types.h>
+.Fd #include <netinet/in.h>
+.Fd #include <libutil.h>
+.Ft int
+.Fn realhostname "char *host" "size_t hsize" "const struct in_addr *ip"
+.Pp
+Link with
+.Va -lutil
+on the
+.Xr cc 1
+command line.
+.Sh DESCRIPTION
+The function
+.Fn realhostname
+converts
+.Ar ip
+to the corresponding host name.  This is done by resolving
+.Ar ip
+to a host name and then ensuring that the host name resolves
+back to
+.Ar ip .
+.Pp
+.Ar host
+must point to a buffer of at least
+.Ar hsize
+bytes, and will always be written to by this function.
+.Pp
+If the name resolution doesn't work both ways or if the host name is longer
+than
+.Ar hsize
+bytes,
+.Xr inet_ntoa 3
+is used to convert
+.Ar ip
+to an ascii form.
+.Pp
+If the string written to
+.Ar host
+is
+.Ar hsize
+bytes long,
+.Ar host
+will not be NUL terminated.
+.Sh RETURN VALUES
+.Fn realhostname
+will return one of the following constants which are defined in
+.Pa libutil.h :
+.Pp
+.Bl -tag -width XXX -offset XXX
+.It Li HOSTNAME_FOUND
+A valid host name was found.
+.It Li HOSTNAME_INCORRECTNAME
+A host name was found, but it did not resolve back to the passed
+.Ar ip .
+.Ar host
+now contains the numeric value of
+.Ar ip .
+.It Li HOSTNAME_INVALIDADDR
+.Ar ip
+could not be resolved.
+.Ar host
+now contains the numeric value of
+.Ar ip .
+.It Li HOSTNAME_INVALIDNAME
+A host name was found, but it could not be resolved back to any ip number.
+.Ar host
+now contains the numeric value of
+.Ar ip .
+.El
+.Sh SEE ALSO
+.Xr gethostbyaddr 3 ,
+.Xr gethostbyname 3 ,
+.Xr inet_ntoa 3
diff --git a/lib/libutil/realhostname.c b/lib/libutil/realhostname.c
new file mode 100644
index 0000000..ff57011
--- /dev/null
+++ b/lib/libutil/realhostname.c
@@ -0,0 +1,73 @@
+/*-
+ * Copyright (c) 1999 Brian Somers <brian@Awfulhak.org>
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ *	$Id:$
+ */
+
+#include <sys/param.h>
+
+#include <sys/socket.h>
+#include <netdb.h>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+
+#include <stdio.h>
+#include <string.h>
+
+#include "libutil.h"
+
+int
+realhostname(char *host, size_t hsize, const struct in_addr *ip)
+{
+	int result;
+	struct hostent *hp;
+
+	result = HOSTNAME_INVALIDADDR;
+	hp = gethostbyaddr((char *)ip, sizeof *ip, AF_INET);
+
+	if (hp != NULL && strlen(hp->h_name) <= hsize) {
+		char lookup[MAXHOSTNAMELEN + 1];
+
+		strncpy(lookup, hp->h_name, sizeof lookup - 1);
+		lookup[sizeof lookup - 1] = '\0';
+		hp = gethostbyname(lookup);
+		if (hp == NULL)
+			result = HOSTNAME_INVALIDNAME;
+		else for (; ; hp->h_addr_list++) {
+			if (hp->h_addr_list[0] == NULL) {
+				result = HOSTNAME_INCORRECTNAME;
+				break;
+			}
+			if (!memcmp(*hp->h_addr_list, ip, sizeof *ip)) {
+				strncpy(host, lookup, hsize);
+				return HOSTNAME_FOUND;
+			}
+		}
+	}
+
+	strncpy(host, inet_ntoa(*ip), hsize);
+
+	return result;
+}