Subject: Re: [iproute2 patch]: Add 'ip tuntap' facility for managing tun/tap devices

From: Stephen Hemminger <[email-masked]>
Date: Wed, 27 May 2009 21:58:23 -0700

On Mon, 04 May 2009 11:42:58 +0100
David Woodhouse <[email-masked]> wrote:

> This patch provides support for 'ip tuntap', allowing creation and
> deletion of persistent tun/tap devices.
> 
> The support for _listing_ devices relies on the patch I just sent to
> netdev (<[email-masked]>), although
> creation and deletion work without that patch.
> 
> diff --git a/ip/Makefile b/ip/Makefile
> index 98ba876..e868f3e 100644
> --- a/ip/Makefile
> +++ b/ip/Makefile
> @@ -1,6 +1,6 @@
>  IPOBJ=ip.o ipaddress.o ipaddrlabel.o iproute.o iprule.o \
>      rtm_map.o iptunnel.o ip6tunnel.o tunnel.o ipneigh.o ipntable.o iplink.o \
> -    ipmaddr.o ipmonitor.o ipmroute.o ipprefix.o \
> +    ipmaddr.o ipmonitor.o ipmroute.o ipprefix.o iptuntap.o \
>      ipxfrm.o xfrm_state.o xfrm_policy.o xfrm_monitor.o \
>      iplink_vlan.o link_veth.o link_gre.o
>  
> diff --git a/ip/ip.c b/ip/ip.c
> index 2bd54b2..d846a76 100644
> --- a/ip/ip.c
> +++ b/ip/ip.c
> @@ -47,7 +47,7 @@ static void usage(void)
>  "Usage: ip [ OPTIONS ] OBJECT { COMMAND | help }\n"
>  "       ip [ -force ] -batch filename\n"
>  "where  OBJECT := { link | addr | addrlabel | route | rule | neigh | ntable |\n"
> -"                   tunnel | maddr | mroute | monitor | xfrm }\n"
> +"                   tunnel | tuntap | maddr | mroute | monitor | xfrm }\n"
>  "       OPTIONS := { -V[ersion] | -s[tatistics] | -d[etails] | -r[esolve] |\n"
>  "                    -f[amily] { inet | inet6 | ipx | dnet | link } |\n"
>  "                    -o[neline] | -t[imestamp] | -b[atch] [filename] }\n");
> @@ -75,6 +75,8 @@ static const struct cmd {
>  	{ "link",	do_iplink },
>  	{ "tunnel",	do_iptunnel },
>  	{ "tunl",	do_iptunnel },
> +	{ "tuntap",	do_iptuntap },
> +	{ "tap",	do_iptuntap },
>  	{ "monitor",	do_ipmonitor },
>  	{ "xfrm",	do_xfrm },
>  	{ "mroute",	do_multiroute },
> diff --git a/ip/ip_common.h b/ip/ip_common.h
> index 273065f..c857667 100644
> --- a/ip/ip_common.h
> +++ b/ip/ip_common.h
> @@ -32,6 +32,7 @@ extern int do_ipneigh(int argc, char **argv);
>  extern int do_ipntable(int argc, char **argv);
>  extern int do_iptunnel(int argc, char **argv);
>  extern int do_ip6tunnel(int argc, char **argv);
> +extern int do_iptuntap(int argc, char **argv);
>  extern int do_iplink(int argc, char **argv);
>  extern int do_ipmonitor(int argc, char **argv);
>  extern int do_multiaddr(int argc, char **argv);
> diff --git a/ip/iptuntap.c b/ip/iptuntap.c
> new file mode 100644
> index 0000000..b480296
> --- /dev/null
> +++ b/ip/iptuntap.c
> @@ -0,0 +1,322 @@
> +/*
> + * iptunnel.c	       "ip tuntap"
> + *
> + *		This program is free software; you can redistribute it and/or
> + *		modify it under the terms of the GNU General Public License
> + *		as published by the Free Software Foundation; either version
> + *		2 of the License, or (at your option) any later version.
> + *
> + * Authors:	David Woodhouse <[email-masked]>
> + *
> + */
> +
> +#include <stdio.h>
> +#include <stdlib.h>
> +#include <string.h>
> +#include <unistd.h>
> +#include <sys/types.h>
> +#include <sys/socket.h>
> +#include <arpa/inet.h>
> +#include <sys/ioctl.h>
> +#include <linux/if.h>
> +#include <linux/if_tun.h>
> +#include <pwd.h>
> +#include <grp.h>
> +#include <fcntl.h>
> +#include <dirent.h>
> +#include <errno.h>
> +
> +#include "rt_names.h"
> +#include "utils.h"
> +#include "ip_common.h"
> +
> +#define TUNDEV "/dev/net/tun"

I know this is historical legacy, but how does this play with network namespaces?

> +
> +static void usage(void) __attribute__((noreturn));
> +
> +static void usage(void)
> +{
> +	fprintf(stderr, "Usage: ip tuntap { add | del } [ dev PHYS_DEV ] \n");
> +	fprintf(stderr, "          [ mode { tun | tap } ] [ user USER ] [ group GROUP ]\n");
> +	fprintf(stderr, "          [ one_queue ] [ no_pi ] [ vnet_hdr ]\n");
> +	fprintf(stderr, "\n");
> +	fprintf(stderr, "Where: USER  := { STRING | NUMBER }\n");
> +	fprintf(stderr, "       GROUP := { STRING | NUMBER }\n");
> +	exit(-1);
> +}
> +
> +static int tap_add_ioctl(struct ifreq *ifr, uid_t uid, gid_t gid)
> +{
> +	int fd = open(TUNDEV, O_RDWR);
> +	int ret = -1;
> +
> +#ifndef IFF_TUN_EXCL
> +#define IFF_TUN_EXCL	0x8000
> +#endif

This shouldn't be here.
It should be defined in include/linux/if_tun.h in kernel source
and then a kernel sanitized version of if_tun.h should be put
in iproute2 source for backwards compatibility.  But why bother
it doesn't seem to be defined or used by current kernel??

> +	ifr->ifr_flags |= IFF_TUN_EXCL;

Would prefer open() next to the test.

> +	if (fd < 0) {
> +		perror("open");
> +		return -1;
> +	}
> +	if (ioctl(fd, TUNSETIFF, ifr)) {
> +		perror("ioctl(TUNSETIFF)");
> +		goto out;
> +	}
> +	if (uid != -1 && ioctl(fd, TUNSETOWNER, uid)) {
> +		perror("ioctl(TUNSETOWNER)");
> +		goto out;
> +	}
> +	if (gid != -1 && ioctl(fd, TUNSETGROUP, gid)) {
> +		perror("ioctl(TUNSETGROUP)");
> +		goto out;
> +	}
> +	if (ioctl(fd, TUNSETPERSIST, 1)) {
> +		perror("ioctl(TUNSETPERSIST)");
> +		goto out;
> +	}
> +	ret = 0;
> + out:
> +	close(fd);
> +	return ret;
> +}
> +
> +static int tap_del_ioctl(struct ifreq *ifr)
> +{
> +	int fd = open(TUNDEV, O_RDWR);
> +	int ret = -1;
> +
> +	if (fd < 0) {
> +		perror("open");
> +		return -1;
> +	}
> +	if (ioctl(fd, TUNSETIFF, ifr)) {
> +		perror("ioctl(TUNSETIFF)");
> +		goto out;
> +	}
> +	if (ioctl(fd, TUNSETPERSIST, 0)) {
> +		perror("ioctl(TUNSETPERSIST)");
> +		goto out;
> +	}
> +	ret = 0;
> + out:
> +	close(fd);
> +	return ret;
> +	
> +}
> +static int parse_args(int argc, char **argv, struct ifreq *ifr, uid_t *uid, gid_t *gid)
> +{
> +	int count = 0;
> +
> +	memset(ifr, 0, sizeof(*ifr));
> +
> +	ifr->ifr_flags |= IFF_NO_PI;
> +
> +	while (argc > 0) {
> +		if (strcmp(*argv, "mode") == 0) {

The argument parsing in ip commands uses matches() rather than strcmp to allow
for partial completion.  

> +			NEXT_ARG();
> +			if (strcmp(*argv, "tun") == 0) {
> +				if (ifr->ifr_flags & IFF_TAP) {
> +					fprintf(stderr,"You managed to ask for more than one tunnel mode.\n");
> +					exit(-1);
> +				}
> +				ifr->ifr_flags |= IFF_TUN;
> +			} else if (strcmp(*argv, "tap") == 0) {
> +				if (ifr->ifr_flags & IFF_TUN) {
> +					fprintf(stderr,"You managed to ask for more than one tunnel mode.\n");
> +					exit(-1);
> +				}
> +				ifr->ifr_flags |= IFF_TAP;
> +			} else {
> +				fprintf(stderr,"Cannot guess tunnel mode.\n");
> +				exit(-1);
> +			}
> +		} else if (uid && strcmp(*argv, "user") == 0) {
> +			char *end;
> +			unsigned long user;
> +
> +			NEXT_ARG();
> +			if (**argv && ((user = strtol(*argv, &end, 10)), !*end))
> +				*uid = user;
> +			else {
> +				struct passwd *pw = getpwnam(*argv);
> +				if (!pw) {
> +					fprintf(stderr, "invalid user \"%s\"\n", *argv);
> +					exit(-1);
> +				}
> +				*uid = pw->pw_uid;
> +			}
> +		} else if (gid && strcmp(*argv, "group") == 0) {
> +			char *end;
> +			unsigned long group;
> +
> +			NEXT_ARG();
> +			
> +			if (**argv && ((group = strtol(*argv, &end, 10)), !*end))
> +				*gid = group;
> +			else {
> +				struct group *gr = getgrnam(*argv);
> +				if (!gr) {
> +					fprintf(stderr, "invalid group \"%s\"\n", *argv);
> +					exit(-1);
> +				}
> +				*gid = gr->gr_gid;
> +			}
> +		} else if (strcmp(*argv, "pi") == 0) {
> +			ifr->ifr_flags &= ~IFF_NO_PI;
> +		} else if (strcmp(*argv, "one_queue") == 0) {
> +			ifr->ifr_flags |= IFF_ONE_QUEUE;
> +		} else if (strcmp(*argv, "vnet_hdr") == 0) {
> +			ifr->ifr_flags |= IFF_VNET_HDR;
> +		} else if (strcmp(*argv, "dev") == 0) {
> +			NEXT_ARG();
> +			strncpy(ifr->ifr_name, *argv, IFNAMSIZ-1);
> +		} else {
> +			if (strcmp(*argv, "name") == 0) {
> +				NEXT_ARG();
> +			} else if (matches(*argv, "help") == 0)
> +				usage();
> +			if (ifr->ifr_name[0])
> +				duparg2("name", *argv);
> +			strncpy(ifr->ifr_name, *argv, IFNAMSIZ);
> +		}
> +		count++;
> +		argc--; argv++;
> +	}
> +
> +	return 0;
> +}
> +
> +
> +static int do_add(int argc, char **argv)
> +{
> +	struct ifreq ifr;
> +	uid_t uid = -1;
> +	gid_t gid = -1;
> +
> +	if (parse_args(argc, argv, &ifr, &uid, &gid) < 0)
> +		return -1;
> +
> +	if (!(ifr.ifr_flags & TUN_TYPE_MASK)) {
> +		fprintf(stderr, "You failed to specify a tunnel mode\n");
> +		return -1;
> +	}
> +	return tap_add_ioctl(&ifr, uid, gid);
> +}
> +
> +static int do_del(int argc, char **argv)
> +{
> +	struct ifreq ifr;
> +
> +	if (parse_args(argc, argv, &ifr, NULL, NULL) < 0)
> +		return -1;
> +
> +	return tap_del_ioctl(&ifr);
> +}
> +
> +static int read_prop(char *dev, char *prop, long *value)
> +{
> +	char fname[IFNAMSIZ+25], buf[80], *endp;
> +	ssize_t len;
> +	int fd;
> +	long result;
> +
> +	sprintf(fname, "/sys/class/net/%s/%s", dev, prop);
> +	fd = open(fname, O_RDONLY);
> +	if (fd < 0) {
> +		if (strcmp(prop, "tun_flags"))
> +			fprintf(stderr, "open %s: %s\n", fname, strerror(errno));
> +		return -1;
> +	}
> +	len = read(fd, buf, sizeof(buf)-1);
> +	close(fd);
> +	if (len < 0) {
> +		fprintf(stderr, "read %s: %s", fname, strerror(errno));
> +		return -1;
> +	}
> +
> +	buf[len] = 0;
> +	result = strtol(buf, &endp, 0);
> +	if (*endp != '\n') {
> +		fprintf(stderr, "Failed to parse %s\n", fname);
> +		return -1;
> +	}
> +	*value = result;
> +	return 0;
> +}
> +
> +static void print_flags(long flags)
> +{
> +	if (flags & IFF_TUN)
> +		printf(" tun");
> +
> +	if (flags & IFF_TAP)
> +		printf(" tap");
> +
> +	if (!(flags & IFF_NO_PI))
> +		printf(" pi");
> +
> +	if (flags & IFF_ONE_QUEUE)
> +		printf(" one_queue");
> +
> +	if (flags & IFF_VNET_HDR)
> +		printf(" vnet_hdr");
> +
> +	flags &= ~(IFF_TUN|IFF_TAP|IFF_NO_PI|IFF_ONE_QUEUE|IFF_VNET_HDR);
> +	if (flags)
> +		printf(" UNKNOWN_FLAGS:%x", flags);
> +}
> +
> +static int do_show(int argc, char **argv)
> +{
> +	DIR *dir;
> +	struct dirent *d;
> +	long flags, owner = -1, group = -1;
> +	int i;
> +
> +	dir = opendir("/sys/class/net");
> +	if (!dir) {
> +		perror("opendir");
> +		return -1;
> +	}
> +	while ((d = readdir(dir))) {
> +		if (d->d_name[0] == '.' &&
> +		    (d->d_name[1] == 0 || d->d_name[1] == '.'))
> +			continue;
> +
> +		if (read_prop(d->d_name, "tun_flags", &flags))
> +			continue;
> +
> +		read_prop(d->d_name, "owner", &owner);
> +		read_prop(d->d_name, "group", &group);
> +		
> +		printf("%s:", d->d_name);
> +		print_flags(flags);
> +		if (owner != -1)
> +			printf(" user %ld", owner);
> +		if (group != -1)
> +			printf(" group %ld", group);
> +		printf("\n");
> +	}
> +	return 0;
> +}
> +
> +int do_iptuntap(int argc, char **argv)
> +{
> +	if (argc > 0) {
> +		if (matches(*argv, "add") == 0)
> +			return do_add(argc-1, argv+1);
> +		if (matches(*argv, "del") == 0)
> +			return do_del(argc-1, argv+1);
> +		if (matches(*argv, "show") == 0 ||
> +                    matches(*argv, "lst") == 0 ||
> +                    matches(*argv, "list") == 0)
> +                        return do_show(argc-1, argv+1);
> +		if (matches(*argv, "help") == 0)
> +			usage();
> +	} else
> +		return do_show(0, NULL);
> +
> +	fprintf(stderr, "Command \"%s\" is unknown, try \"ip tuntap help\".\n", *argv);
> +	exit(-1);
> +}
> 

--