qemu-e2k/qemu-bridge-helper.c

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/*
* QEMU Bridge Helper
*
* Copyright IBM, Corp. 2011
*
* Authors:
* Anthony Liguori <aliguori@us.ibm.com>
* Richa Marwaha <rmarwah@linux.vnet.ibm.com>
* Corey Bryant <coreyb@linux.vnet.ibm.com>
*
* This work is licensed under the terms of the GNU GPL, version 2. See
* the COPYING file in the top-level directory.
*
*/
#include "qemu/osdep.h"
Add access control support to qemu bridge helper We go to great lengths to restrict ourselves to just cap_net_admin as an OS enforced security mechanism. However, we further restrict what we allow users to do to simply adding a tap device to a bridge interface by virtue of the fact that this is the only functionality we expose. This is not good enough though. An administrator is likely to want to restrict the bridges that an unprivileged user can access, in particular, to restrict an unprivileged user from putting a guest on what should be isolated networks. This patch implements an ACL mechanism that is enforced by qemu-bridge-helper. The ACLs are fairly simple whitelist/blacklist mechanisms with a wildcard of 'all'. All users are blacklisted by default, and deny takes precedence over allow. An interesting feature of this ACL mechanism is that you can include external ACL files. The main reason to support this is so that you can set different file system permissions on those external ACL files. This allows an administrator to implement rather sophisticated ACL policies based on user/group policies via the file system. As an example: /etc/qemu/bridge.conf root:qemu 0640 allow br0 include /etc/qemu/alice.conf include /etc/qemu/bob.conf include /etc/qemu/charlie.conf /etc/qemu/alice.conf root:alice 0640 allow br1 /etc/qemu/bob.conf root:bob 0640 allow br2 /etc/qemu/charlie.conf root:charlie 0640 deny all This ACL pattern allows any user in the qemu group to get a tap device connected to br0 (which is bridged to the physical network). Users in the alice group can additionally get a tap device connected to br1. This allows br1 to act as a private bridge for the alice group. Users in the bob group can additionally get a tap device connected to br2. This allows br2 to act as a private bridge for the bob group. Users in the charlie group cannot get a tap device connected to any bridge. Under no circumstance can the bob group get access to br1 or can the alice group get access to br2. And under no cicumstance can the charlie group get access to any bridge. Signed-off-by: Anthony Liguori <aliguori@us.ibm.com> Signed-off-by: Richa Marwaha <rmarwah@linux.vnet.ibm.com> Signed-off-by: Corey Bryant <coreyb@linux.vnet.ibm.com> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
2012-01-26 15:42:25 +01:00
#include <glib.h>
#include <sys/ioctl.h>
#include <sys/socket.h>
#include <sys/un.h>
#include <sys/prctl.h>
#include <net/if.h>
#include <linux/sockios.h>
#ifndef SIOCBRADDIF
#include <linux/if_bridge.h>
#endif
#include "qemu/queue.h"
Add access control support to qemu bridge helper We go to great lengths to restrict ourselves to just cap_net_admin as an OS enforced security mechanism. However, we further restrict what we allow users to do to simply adding a tap device to a bridge interface by virtue of the fact that this is the only functionality we expose. This is not good enough though. An administrator is likely to want to restrict the bridges that an unprivileged user can access, in particular, to restrict an unprivileged user from putting a guest on what should be isolated networks. This patch implements an ACL mechanism that is enforced by qemu-bridge-helper. The ACLs are fairly simple whitelist/blacklist mechanisms with a wildcard of 'all'. All users are blacklisted by default, and deny takes precedence over allow. An interesting feature of this ACL mechanism is that you can include external ACL files. The main reason to support this is so that you can set different file system permissions on those external ACL files. This allows an administrator to implement rather sophisticated ACL policies based on user/group policies via the file system. As an example: /etc/qemu/bridge.conf root:qemu 0640 allow br0 include /etc/qemu/alice.conf include /etc/qemu/bob.conf include /etc/qemu/charlie.conf /etc/qemu/alice.conf root:alice 0640 allow br1 /etc/qemu/bob.conf root:bob 0640 allow br2 /etc/qemu/charlie.conf root:charlie 0640 deny all This ACL pattern allows any user in the qemu group to get a tap device connected to br0 (which is bridged to the physical network). Users in the alice group can additionally get a tap device connected to br1. This allows br1 to act as a private bridge for the alice group. Users in the bob group can additionally get a tap device connected to br2. This allows br2 to act as a private bridge for the bob group. Users in the charlie group cannot get a tap device connected to any bridge. Under no circumstance can the bob group get access to br1 or can the alice group get access to br2. And under no cicumstance can the charlie group get access to any bridge. Signed-off-by: Anthony Liguori <aliguori@us.ibm.com> Signed-off-by: Richa Marwaha <rmarwah@linux.vnet.ibm.com> Signed-off-by: Corey Bryant <coreyb@linux.vnet.ibm.com> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
2012-01-26 15:42:25 +01:00
#include "net/tap-linux.h"
#ifdef CONFIG_LIBCAP
#include <cap-ng.h>
#endif
Add access control support to qemu bridge helper We go to great lengths to restrict ourselves to just cap_net_admin as an OS enforced security mechanism. However, we further restrict what we allow users to do to simply adding a tap device to a bridge interface by virtue of the fact that this is the only functionality we expose. This is not good enough though. An administrator is likely to want to restrict the bridges that an unprivileged user can access, in particular, to restrict an unprivileged user from putting a guest on what should be isolated networks. This patch implements an ACL mechanism that is enforced by qemu-bridge-helper. The ACLs are fairly simple whitelist/blacklist mechanisms with a wildcard of 'all'. All users are blacklisted by default, and deny takes precedence over allow. An interesting feature of this ACL mechanism is that you can include external ACL files. The main reason to support this is so that you can set different file system permissions on those external ACL files. This allows an administrator to implement rather sophisticated ACL policies based on user/group policies via the file system. As an example: /etc/qemu/bridge.conf root:qemu 0640 allow br0 include /etc/qemu/alice.conf include /etc/qemu/bob.conf include /etc/qemu/charlie.conf /etc/qemu/alice.conf root:alice 0640 allow br1 /etc/qemu/bob.conf root:bob 0640 allow br2 /etc/qemu/charlie.conf root:charlie 0640 deny all This ACL pattern allows any user in the qemu group to get a tap device connected to br0 (which is bridged to the physical network). Users in the alice group can additionally get a tap device connected to br1. This allows br1 to act as a private bridge for the alice group. Users in the bob group can additionally get a tap device connected to br2. This allows br2 to act as a private bridge for the bob group. Users in the charlie group cannot get a tap device connected to any bridge. Under no circumstance can the bob group get access to br1 or can the alice group get access to br2. And under no cicumstance can the charlie group get access to any bridge. Signed-off-by: Anthony Liguori <aliguori@us.ibm.com> Signed-off-by: Richa Marwaha <rmarwah@linux.vnet.ibm.com> Signed-off-by: Corey Bryant <coreyb@linux.vnet.ibm.com> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
2012-01-26 15:42:25 +01:00
#define DEFAULT_ACL_FILE CONFIG_QEMU_CONFDIR "/bridge.conf"
enum {
ACL_ALLOW = 0,
ACL_ALLOW_ALL,
ACL_DENY,
ACL_DENY_ALL,
};
typedef struct ACLRule {
int type;
char iface[IFNAMSIZ];
QSIMPLEQ_ENTRY(ACLRule) entry;
} ACLRule;
typedef QSIMPLEQ_HEAD(ACLList, ACLRule) ACLList;
static void usage(void)
{
fprintf(stderr,
"Usage: qemu-bridge-helper [--use-vnet] --br=bridge --fd=unixfd\n");
}
Add access control support to qemu bridge helper We go to great lengths to restrict ourselves to just cap_net_admin as an OS enforced security mechanism. However, we further restrict what we allow users to do to simply adding a tap device to a bridge interface by virtue of the fact that this is the only functionality we expose. This is not good enough though. An administrator is likely to want to restrict the bridges that an unprivileged user can access, in particular, to restrict an unprivileged user from putting a guest on what should be isolated networks. This patch implements an ACL mechanism that is enforced by qemu-bridge-helper. The ACLs are fairly simple whitelist/blacklist mechanisms with a wildcard of 'all'. All users are blacklisted by default, and deny takes precedence over allow. An interesting feature of this ACL mechanism is that you can include external ACL files. The main reason to support this is so that you can set different file system permissions on those external ACL files. This allows an administrator to implement rather sophisticated ACL policies based on user/group policies via the file system. As an example: /etc/qemu/bridge.conf root:qemu 0640 allow br0 include /etc/qemu/alice.conf include /etc/qemu/bob.conf include /etc/qemu/charlie.conf /etc/qemu/alice.conf root:alice 0640 allow br1 /etc/qemu/bob.conf root:bob 0640 allow br2 /etc/qemu/charlie.conf root:charlie 0640 deny all This ACL pattern allows any user in the qemu group to get a tap device connected to br0 (which is bridged to the physical network). Users in the alice group can additionally get a tap device connected to br1. This allows br1 to act as a private bridge for the alice group. Users in the bob group can additionally get a tap device connected to br2. This allows br2 to act as a private bridge for the bob group. Users in the charlie group cannot get a tap device connected to any bridge. Under no circumstance can the bob group get access to br1 or can the alice group get access to br2. And under no cicumstance can the charlie group get access to any bridge. Signed-off-by: Anthony Liguori <aliguori@us.ibm.com> Signed-off-by: Richa Marwaha <rmarwah@linux.vnet.ibm.com> Signed-off-by: Corey Bryant <coreyb@linux.vnet.ibm.com> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
2012-01-26 15:42:25 +01:00
static int parse_acl_file(const char *filename, ACLList *acl_list)
{
FILE *f;
char line[4096];
ACLRule *acl_rule;
f = fopen(filename, "r");
if (f == NULL) {
return -1;
}
while (fgets(line, sizeof(line), f) != NULL) {
char *ptr = line;
char *cmd, *arg, *argend;
while (isspace(*ptr)) {
ptr++;
}
/* skip comments and empty lines */
if (*ptr == '#' || *ptr == 0) {
continue;
}
cmd = ptr;
arg = strchr(cmd, ' ');
if (arg == NULL) {
arg = strchr(cmd, '\t');
}
if (arg == NULL) {
fprintf(stderr, "Invalid config line:\n %s\n", line);
fclose(f);
errno = EINVAL;
return -1;
}
*arg = 0;
arg++;
while (isspace(*arg)) {
arg++;
}
argend = arg + strlen(arg);
while (arg != argend && isspace(*(argend - 1))) {
argend--;
}
*argend = 0;
if (strcmp(cmd, "deny") == 0) {
acl_rule = g_malloc(sizeof(*acl_rule));
if (strcmp(arg, "all") == 0) {
acl_rule->type = ACL_DENY_ALL;
} else {
acl_rule->type = ACL_DENY;
snprintf(acl_rule->iface, IFNAMSIZ, "%s", arg);
}
QSIMPLEQ_INSERT_TAIL(acl_list, acl_rule, entry);
} else if (strcmp(cmd, "allow") == 0) {
acl_rule = g_malloc(sizeof(*acl_rule));
if (strcmp(arg, "all") == 0) {
acl_rule->type = ACL_ALLOW_ALL;
} else {
acl_rule->type = ACL_ALLOW;
snprintf(acl_rule->iface, IFNAMSIZ, "%s", arg);
}
QSIMPLEQ_INSERT_TAIL(acl_list, acl_rule, entry);
} else if (strcmp(cmd, "include") == 0) {
/* ignore errors */
parse_acl_file(arg, acl_list);
} else {
fprintf(stderr, "Unknown command `%s'\n", cmd);
fclose(f);
errno = EINVAL;
return -1;
}
}
fclose(f);
return 0;
}
static bool has_vnet_hdr(int fd)
{
unsigned int features = 0;
if (ioctl(fd, TUNGETFEATURES, &features) == -1) {
return false;
}
if (!(features & IFF_VNET_HDR)) {
return false;
}
return true;
}
static void prep_ifreq(struct ifreq *ifr, const char *ifname)
{
memset(ifr, 0, sizeof(*ifr));
snprintf(ifr->ifr_name, IFNAMSIZ, "%s", ifname);
}
static int send_fd(int c, int fd)
{
char msgbuf[CMSG_SPACE(sizeof(fd))];
struct msghdr msg = {
.msg_control = msgbuf,
.msg_controllen = sizeof(msgbuf),
};
struct cmsghdr *cmsg;
struct iovec iov;
char req[1] = { 0x00 };
cmsg = CMSG_FIRSTHDR(&msg);
cmsg->cmsg_level = SOL_SOCKET;
cmsg->cmsg_type = SCM_RIGHTS;
cmsg->cmsg_len = CMSG_LEN(sizeof(fd));
msg.msg_controllen = cmsg->cmsg_len;
iov.iov_base = req;
iov.iov_len = sizeof(req);
msg.msg_iov = &iov;
msg.msg_iovlen = 1;
memcpy(CMSG_DATA(cmsg), &fd, sizeof(fd));
return sendmsg(c, &msg, 0);
}
#ifdef CONFIG_LIBCAP
static int drop_privileges(void)
{
/* clear all capabilities */
capng_clear(CAPNG_SELECT_BOTH);
if (capng_update(CAPNG_ADD, CAPNG_EFFECTIVE | CAPNG_PERMITTED,
CAP_NET_ADMIN) < 0) {
return -1;
}
/* change to calling user's real uid and gid, retaining supplemental
* groups and CAP_NET_ADMIN */
if (capng_change_id(getuid(), getgid(), CAPNG_CLEAR_BOUNDING)) {
return -1;
}
return 0;
}
#endif
int main(int argc, char **argv)
{
struct ifreq ifr;
#ifndef SIOCBRADDIF
unsigned long ifargs[4];
#endif
int ifindex;
int fd = -1, ctlfd = -1, unixfd = -1;
int use_vnet = 0;
int mtu;
const char *bridge = NULL;
char iface[IFNAMSIZ];
int index;
Add access control support to qemu bridge helper We go to great lengths to restrict ourselves to just cap_net_admin as an OS enforced security mechanism. However, we further restrict what we allow users to do to simply adding a tap device to a bridge interface by virtue of the fact that this is the only functionality we expose. This is not good enough though. An administrator is likely to want to restrict the bridges that an unprivileged user can access, in particular, to restrict an unprivileged user from putting a guest on what should be isolated networks. This patch implements an ACL mechanism that is enforced by qemu-bridge-helper. The ACLs are fairly simple whitelist/blacklist mechanisms with a wildcard of 'all'. All users are blacklisted by default, and deny takes precedence over allow. An interesting feature of this ACL mechanism is that you can include external ACL files. The main reason to support this is so that you can set different file system permissions on those external ACL files. This allows an administrator to implement rather sophisticated ACL policies based on user/group policies via the file system. As an example: /etc/qemu/bridge.conf root:qemu 0640 allow br0 include /etc/qemu/alice.conf include /etc/qemu/bob.conf include /etc/qemu/charlie.conf /etc/qemu/alice.conf root:alice 0640 allow br1 /etc/qemu/bob.conf root:bob 0640 allow br2 /etc/qemu/charlie.conf root:charlie 0640 deny all This ACL pattern allows any user in the qemu group to get a tap device connected to br0 (which is bridged to the physical network). Users in the alice group can additionally get a tap device connected to br1. This allows br1 to act as a private bridge for the alice group. Users in the bob group can additionally get a tap device connected to br2. This allows br2 to act as a private bridge for the bob group. Users in the charlie group cannot get a tap device connected to any bridge. Under no circumstance can the bob group get access to br1 or can the alice group get access to br2. And under no cicumstance can the charlie group get access to any bridge. Signed-off-by: Anthony Liguori <aliguori@us.ibm.com> Signed-off-by: Richa Marwaha <rmarwah@linux.vnet.ibm.com> Signed-off-by: Corey Bryant <coreyb@linux.vnet.ibm.com> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
2012-01-26 15:42:25 +01:00
ACLRule *acl_rule;
ACLList acl_list;
int access_allowed, access_denied;
int ret = EXIT_SUCCESS;
#ifdef CONFIG_LIBCAP
/* if we're run from an suid binary, immediately drop privileges preserving
* cap_net_admin */
if (geteuid() == 0 && getuid() != geteuid()) {
if (drop_privileges() == -1) {
fprintf(stderr, "failed to drop privileges\n");
return 1;
}
}
#endif
/* parse arguments */
for (index = 1; index < argc; index++) {
if (strcmp(argv[index], "--use-vnet") == 0) {
use_vnet = 1;
} else if (strncmp(argv[index], "--br=", 5) == 0) {
bridge = &argv[index][5];
} else if (strncmp(argv[index], "--fd=", 5) == 0) {
unixfd = atoi(&argv[index][5]);
} else {
usage();
return EXIT_FAILURE;
}
}
if (bridge == NULL || unixfd == -1) {
usage();
return EXIT_FAILURE;
}
Add access control support to qemu bridge helper We go to great lengths to restrict ourselves to just cap_net_admin as an OS enforced security mechanism. However, we further restrict what we allow users to do to simply adding a tap device to a bridge interface by virtue of the fact that this is the only functionality we expose. This is not good enough though. An administrator is likely to want to restrict the bridges that an unprivileged user can access, in particular, to restrict an unprivileged user from putting a guest on what should be isolated networks. This patch implements an ACL mechanism that is enforced by qemu-bridge-helper. The ACLs are fairly simple whitelist/blacklist mechanisms with a wildcard of 'all'. All users are blacklisted by default, and deny takes precedence over allow. An interesting feature of this ACL mechanism is that you can include external ACL files. The main reason to support this is so that you can set different file system permissions on those external ACL files. This allows an administrator to implement rather sophisticated ACL policies based on user/group policies via the file system. As an example: /etc/qemu/bridge.conf root:qemu 0640 allow br0 include /etc/qemu/alice.conf include /etc/qemu/bob.conf include /etc/qemu/charlie.conf /etc/qemu/alice.conf root:alice 0640 allow br1 /etc/qemu/bob.conf root:bob 0640 allow br2 /etc/qemu/charlie.conf root:charlie 0640 deny all This ACL pattern allows any user in the qemu group to get a tap device connected to br0 (which is bridged to the physical network). Users in the alice group can additionally get a tap device connected to br1. This allows br1 to act as a private bridge for the alice group. Users in the bob group can additionally get a tap device connected to br2. This allows br2 to act as a private bridge for the bob group. Users in the charlie group cannot get a tap device connected to any bridge. Under no circumstance can the bob group get access to br1 or can the alice group get access to br2. And under no cicumstance can the charlie group get access to any bridge. Signed-off-by: Anthony Liguori <aliguori@us.ibm.com> Signed-off-by: Richa Marwaha <rmarwah@linux.vnet.ibm.com> Signed-off-by: Corey Bryant <coreyb@linux.vnet.ibm.com> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
2012-01-26 15:42:25 +01:00
/* parse default acl file */
QSIMPLEQ_INIT(&acl_list);
if (parse_acl_file(DEFAULT_ACL_FILE, &acl_list) == -1) {
fprintf(stderr, "failed to parse default acl file `%s'\n",
DEFAULT_ACL_FILE);
ret = EXIT_FAILURE;
goto cleanup;
}
/* validate bridge against acl -- default policy is to deny
* according acl policy if we have a deny and allow both
* then deny should always win over allow
*/
access_allowed = 0;
access_denied = 0;
QSIMPLEQ_FOREACH(acl_rule, &acl_list, entry) {
switch (acl_rule->type) {
case ACL_ALLOW_ALL:
access_allowed = 1;
break;
case ACL_ALLOW:
if (strcmp(bridge, acl_rule->iface) == 0) {
access_allowed = 1;
}
break;
case ACL_DENY_ALL:
access_denied = 1;
break;
case ACL_DENY:
if (strcmp(bridge, acl_rule->iface) == 0) {
access_denied = 1;
}
break;
}
}
if ((access_allowed == 0) || (access_denied == 1)) {
fprintf(stderr, "access denied by acl file\n");
ret = EXIT_FAILURE;
goto cleanup;
}
/* open a socket to use to control the network interfaces */
ctlfd = socket(AF_INET, SOCK_STREAM, 0);
if (ctlfd == -1) {
fprintf(stderr, "failed to open control socket: %s\n", strerror(errno));
ret = EXIT_FAILURE;
goto cleanup;
}
/* open the tap device */
fd = open("/dev/net/tun", O_RDWR);
if (fd == -1) {
fprintf(stderr, "failed to open /dev/net/tun: %s\n", strerror(errno));
ret = EXIT_FAILURE;
goto cleanup;
}
/* request a tap device, disable PI, and add vnet header support if
* requested and it's available. */
prep_ifreq(&ifr, "tap%d");
ifr.ifr_flags = IFF_TAP|IFF_NO_PI;
if (use_vnet && has_vnet_hdr(fd)) {
ifr.ifr_flags |= IFF_VNET_HDR;
}
if (ioctl(fd, TUNSETIFF, &ifr) == -1) {
fprintf(stderr, "failed to create tun device: %s\n", strerror(errno));
ret = EXIT_FAILURE;
goto cleanup;
}
/* save tap device name */
snprintf(iface, sizeof(iface), "%s", ifr.ifr_name);
/* get the mtu of the bridge */
prep_ifreq(&ifr, bridge);
if (ioctl(ctlfd, SIOCGIFMTU, &ifr) == -1) {
fprintf(stderr, "failed to get mtu of bridge `%s': %s\n",
bridge, strerror(errno));
ret = EXIT_FAILURE;
goto cleanup;
}
/* save mtu */
mtu = ifr.ifr_mtu;
/* set the mtu of the interface based on the bridge */
prep_ifreq(&ifr, iface);
ifr.ifr_mtu = mtu;
if (ioctl(ctlfd, SIOCSIFMTU, &ifr) == -1) {
fprintf(stderr, "failed to set mtu of device `%s' to %d: %s\n",
iface, mtu, strerror(errno));
ret = EXIT_FAILURE;
goto cleanup;
}
/* Linux uses the lowest enslaved MAC address as the MAC address of
* the bridge. Set MAC address to a high value so that it doesn't
* affect the MAC address of the bridge.
*/
if (ioctl(ctlfd, SIOCGIFHWADDR, &ifr) < 0) {
fprintf(stderr, "failed to get MAC address of device `%s': %s\n",
iface, strerror(errno));
ret = EXIT_FAILURE;
goto cleanup;
}
ifr.ifr_hwaddr.sa_data[0] = 0xFE;
if (ioctl(ctlfd, SIOCSIFHWADDR, &ifr) < 0) {
fprintf(stderr, "failed to set MAC address of device `%s': %s\n",
iface, strerror(errno));
ret = EXIT_FAILURE;
goto cleanup;
}
/* add the interface to the bridge */
prep_ifreq(&ifr, bridge);
ifindex = if_nametoindex(iface);
#ifndef SIOCBRADDIF
ifargs[0] = BRCTL_ADD_IF;
ifargs[1] = ifindex;
ifargs[2] = 0;
ifargs[3] = 0;
ifr.ifr_data = (void *)ifargs;
ret = ioctl(ctlfd, SIOCDEVPRIVATE, &ifr);
#else
ifr.ifr_ifindex = ifindex;
ret = ioctl(ctlfd, SIOCBRADDIF, &ifr);
#endif
if (ret == -1) {
fprintf(stderr, "failed to add interface `%s' to bridge `%s': %s\n",
iface, bridge, strerror(errno));
ret = EXIT_FAILURE;
goto cleanup;
}
/* bring the interface up */
prep_ifreq(&ifr, iface);
if (ioctl(ctlfd, SIOCGIFFLAGS, &ifr) == -1) {
fprintf(stderr, "failed to get interface flags for `%s': %s\n",
iface, strerror(errno));
ret = EXIT_FAILURE;
goto cleanup;
}
ifr.ifr_flags |= IFF_UP;
if (ioctl(ctlfd, SIOCSIFFLAGS, &ifr) == -1) {
fprintf(stderr, "failed to bring up interface `%s': %s\n",
iface, strerror(errno));
ret = EXIT_FAILURE;
goto cleanup;
}
/* write fd to the domain socket */
if (send_fd(unixfd, fd) == -1) {
fprintf(stderr, "failed to write fd to unix socket: %s\n",
strerror(errno));
ret = EXIT_FAILURE;
goto cleanup;
}
/* ... */
/* profit! */
cleanup:
if (fd >= 0) {
close(fd);
}
if (ctlfd >= 0) {
close(ctlfd);
}
Add access control support to qemu bridge helper We go to great lengths to restrict ourselves to just cap_net_admin as an OS enforced security mechanism. However, we further restrict what we allow users to do to simply adding a tap device to a bridge interface by virtue of the fact that this is the only functionality we expose. This is not good enough though. An administrator is likely to want to restrict the bridges that an unprivileged user can access, in particular, to restrict an unprivileged user from putting a guest on what should be isolated networks. This patch implements an ACL mechanism that is enforced by qemu-bridge-helper. The ACLs are fairly simple whitelist/blacklist mechanisms with a wildcard of 'all'. All users are blacklisted by default, and deny takes precedence over allow. An interesting feature of this ACL mechanism is that you can include external ACL files. The main reason to support this is so that you can set different file system permissions on those external ACL files. This allows an administrator to implement rather sophisticated ACL policies based on user/group policies via the file system. As an example: /etc/qemu/bridge.conf root:qemu 0640 allow br0 include /etc/qemu/alice.conf include /etc/qemu/bob.conf include /etc/qemu/charlie.conf /etc/qemu/alice.conf root:alice 0640 allow br1 /etc/qemu/bob.conf root:bob 0640 allow br2 /etc/qemu/charlie.conf root:charlie 0640 deny all This ACL pattern allows any user in the qemu group to get a tap device connected to br0 (which is bridged to the physical network). Users in the alice group can additionally get a tap device connected to br1. This allows br1 to act as a private bridge for the alice group. Users in the bob group can additionally get a tap device connected to br2. This allows br2 to act as a private bridge for the bob group. Users in the charlie group cannot get a tap device connected to any bridge. Under no circumstance can the bob group get access to br1 or can the alice group get access to br2. And under no cicumstance can the charlie group get access to any bridge. Signed-off-by: Anthony Liguori <aliguori@us.ibm.com> Signed-off-by: Richa Marwaha <rmarwah@linux.vnet.ibm.com> Signed-off-by: Corey Bryant <coreyb@linux.vnet.ibm.com> Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
2012-01-26 15:42:25 +01:00
while ((acl_rule = QSIMPLEQ_FIRST(&acl_list)) != NULL) {
QSIMPLEQ_REMOVE_HEAD(&acl_list, entry);
g_free(acl_rule);
}
return ret;
}