From patchwork Thu Oct 6 15:38:26 2011 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Richa Marwaha X-Patchwork-Id: 118111 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from lists.gnu.org (lists.gnu.org [140.186.70.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (Client did not present a certificate) by ozlabs.org (Postfix) with ESMTPS id CB68FB7091 for ; Fri, 7 Oct 2011 02:39:52 +1100 (EST) Received: from localhost ([::1]:48313 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RBq2t-0004RZ-Eu for incoming@patchwork.ozlabs.org; Thu, 06 Oct 2011 11:39:39 -0400 Received: from eggs.gnu.org ([140.186.70.92]:37387) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RBq2l-0004E9-Eh for qemu-devel@nongnu.org; Thu, 06 Oct 2011 11:39:32 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1RBq2j-0004um-8d for qemu-devel@nongnu.org; Thu, 06 Oct 2011 11:39:31 -0400 Received: from e9.ny.us.ibm.com ([32.97.182.139]:35844) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1RBq2j-0004hW-2z for qemu-devel@nongnu.org; Thu, 06 Oct 2011 11:39:29 -0400 Received: from d01relay01.pok.ibm.com (d01relay01.pok.ibm.com [9.56.227.233]) by e9.ny.us.ibm.com (8.14.4/8.13.1) with ESMTP id p96F36Tk022162 for ; Thu, 6 Oct 2011 11:03:06 -0400 Received: from d01av04.pok.ibm.com (d01av04.pok.ibm.com [9.56.224.64]) by d01relay01.pok.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id p96FcrSM230094 for ; Thu, 6 Oct 2011 11:38:54 -0400 Received: from d01av04.pok.ibm.com (loopback [127.0.0.1]) by d01av04.pok.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id p96FclnF013959 for ; Thu, 6 Oct 2011 11:38:47 -0400 Received: from localhost (richa-laptop-009056115168.pok.ibm.com [9.56.115.168]) by d01av04.pok.ibm.com (8.14.4/8.13.1/NCO v10.0 AVin) with ESMTP id p96FckwY013891; Thu, 6 Oct 2011 11:38:46 -0400 From: Richa Marwaha To: qemu-devel@nongnu.org Date: Thu, 6 Oct 2011 11:38:26 -0400 Message-Id: <1317915508-15491-3-git-send-email-rmarwah@linux.vnet.ibm.com> X-Mailer: git-send-email 1.7.0.4 In-Reply-To: <1317915508-15491-1-git-send-email-rmarwah@linux.vnet.ibm.com> References: <1317915508-15491-1-git-send-email-rmarwah@linux.vnet.ibm.com> X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.6, seldom 2.4 (older, 4) X-Received-From: 32.97.182.139 Cc: aliguori@us.ibm.com, coreyb@linux.vnet.ibm.com, Richa Marwaha Subject: [Qemu-devel] [PATCH 2/4] Add access control support to qemu-bridge-helper X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org 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 a ACL mechanism that is enforced by qemu-bridge-helper. The ACLs are fairly simple whitelist/blacklist mechanisms with a wildcard of 'all'. 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 sophisicated ACL policies based on user/group policies via the file system. As an example: /etc/qemu/bridge.conf root:qemu 0640 deny all allow br0 include /etc/qemu/alice.conf include /etc/qemu/bob.conf /etc/qemu/alice.conf root:alice 0640 allow br1 /etc/qemu/bob.conf root:bob 0640 allow br2 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. Under no circumstance can the bob group get access to br1 or can the alice group get access to br2. Signed-off-by: Richa Marwaha --- qemu-bridge-helper.c | 141 ++++++++++++++++++++++++++++++++++++++++++++++++++ 1 files changed, 141 insertions(+), 0 deletions(-) diff --git a/qemu-bridge-helper.c b/qemu-bridge-helper.c index 4ac7b36..5e09fea 100644 --- a/qemu-bridge-helper.c +++ b/qemu-bridge-helper.c @@ -33,6 +33,105 @@ #include "net/tap-linux.h" +#define MAX_ACLS (128) +#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]; +} ACLRule; + +static int parse_acl_file(const char *filename, ACLRule *acls, int *pacl_count) +{ + int acl_count = *pacl_count; + FILE *f; + char line[4096]; + + f = fopen(filename, "r"); + if (f == NULL) { + return -1; + } + + while (acl_count != MAX_ACLS && + 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) { + if (strcmp(arg, "all") == 0) { + acls[acl_count].type = ACL_DENY_ALL; + } else { + acls[acl_count].type = ACL_DENY; + snprintf(acls[acl_count].iface, IFNAMSIZ, "%s", arg); + } + acl_count++; + } else if (strcmp(cmd, "allow") == 0) { + if (strcmp(arg, "all") == 0) { + acls[acl_count].type = ACL_ALLOW_ALL; + } else { + acls[acl_count].type = ACL_ALLOW; + snprintf(acls[acl_count].iface, IFNAMSIZ, "%s", arg); + } + acl_count++; + } else if (strcmp(cmd, "include") == 0) { + /* ignore errors */ + parse_acl_file(arg, acls, &acl_count); + } else { + fprintf(stderr, "Unknown command `%s'\n", cmd); + fclose(f); + errno = EINVAL; + return -1; + } + } + + *pacl_count = acl_count; + + fclose(f); + + return 0; +} + static int has_vnet_hdr(int fd) { unsigned int features = 0; @@ -95,6 +194,9 @@ int main(int argc, char **argv) const char *bridge; char iface[IFNAMSIZ]; int index; + ACLRule acls[MAX_ACLS]; + int acl_count = 0; + int i, access_allowed, access_denied; /* parse arguments */ if (argc < 3 || argc > 4) { @@ -115,6 +217,45 @@ int main(int argc, char **argv) bridge = argv[index++]; unixfd = atoi(argv[index++]); + /* parse default acl file */ + if (parse_acl_file(DEFAULT_ACL_FILE, acls, &acl_count) == -1) { + fprintf(stderr, "failed to parse default acl file `%s'\n", + DEFAULT_ACL_FILE); + return -errno; + } + + /* 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; + for (i = 0; i < acl_count; i++) { + switch (acls[i].type) { + case ACL_ALLOW_ALL: + access_allowed = 1; + break; + case ACL_ALLOW: + if (strcmp(bridge, acls[i].iface) == 0) { + access_allowed = 1; + } + break; + case ACL_DENY_ALL: + access_denied = 1; + break; + case ACL_DENY: + if (strcmp(bridge, acls[i].iface) == 0) { + access_denied = 1; + } + break; + } + } + + if ((access_allowed == 0) || (access_denied == 1)) { + fprintf(stderr, "access denied by acl file\n"); + return -EPERM; + } + /* open a socket to use to control the network interfaces */ ctlfd = socket(AF_INET, SOCK_STREAM, 0); if (ctlfd == -1) {