Support ACLs for controlling VNC access ("Daniel P. Berrange")

This patch introduces a generic internal API for access control lists
to be used by network servers in QEMU. It adds support for checking
these ACL in the VNC server, in two places. The first ACL is for the
SASL authentication mechanism, checking the SASL username. This ACL
is called 'vnc.username'. The second is for the TLS authentication
mechanism, when x509 client certificates are turned on, checking against
the Distinguished Name of the client. This ACL is called 'vnc.x509dname'

The internal API provides for an ACL with the following characteristics

 - A unique name, eg  vnc.username, and vnc.x509dname.
 - A default policy, allow or deny
 - An ordered series of match rules, with allow or deny policy

If none of the match rules apply, then the default policy is
used.

There is a monitor API to manipulate the ACLs, which I'll describe via
examples

  (qemu) acl show vnc.username
  policy: allow
  (qemu) acl policy vnc.username denya
  acl: policy set to 'deny'
  (qemu) acl allow vnc.username fred
  acl: added rule at position 1
  (qemu) acl allow vnc.username bob
  acl: added rule at position 2
  (qemu) acl allow vnc.username joe 1
  acl: added rule at position 1
  (qemu) acl show vnc.username
  policy: deny
  0: allow fred
  1: allow joe
  2: allow bob


  (qemu) acl show vnc.x509dname
  policy: allow
  (qemu) acl policy vnc.x509dname deny
  acl: policy set to 'deny'
  (qemu) acl allow vnc.x509dname C=GB,O=ACME,L=London,CN=*
  acl: added rule at position 1
  (qemu) acl allow vnc.x509dname C=GB,O=ACME,L=Boston,CN=bob
  acl: added rule at position 2
  (qemu) acl show vnc.x509dname
  policy: deny
  0: allow C=GB,O=ACME,L=London,CN=*
  1: allow C=GB,O=ACME,L=Boston,CN=bob

By default the VNC server will not use any ACLs, allowing access to
the server if the user successfully authenticates. To enable use of
ACLs to restrict user access, the ',acl' flag should be given when
starting QEMU. The initial ACL activated will be a 'deny all' policy
and should be customized using monitor commands.

eg enable SASL auth and ACLs

    qemu ....  -vnc localhost:1,sasl,acl

The next patch will provide a way to load a pre-defined ACL when
starting up


 Makefile        |    6 +
 b/acl.c         |  185 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 b/acl.h         |   74 ++++++++++++++++++++++
 configure       |   18 +++++
 monitor.c       |   95 ++++++++++++++++++++++++++++
 qemu-doc.texi   |   49 ++++++++++++++
 vnc-auth-sasl.c |   16 +++-
 vnc-auth-sasl.h |    7 ++
 vnc-tls.c       |   19 +++++
 vnc-tls.h       |    3 
 vnc.c           |   21 ++++++
 vnc.h           |    3 
 12 files changed, 491 insertions(+), 5 deletions(-)
Signed-off-by: NDaniel P. Berrange <berrange@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>


git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6726 c046a42c-6fe2-441c-8c8c-71466251a162

Makefile

@@ -144,7 +144,7 @@ endif
 ifdef CONFIG_CURSES
 OBJS+=curses.o
 endif
-OBJS+=vnc.o d3des.o
+OBJS+=vnc.o acl.o d3des.o
 ifdef CONFIG_VNC_TLS
 OBJS+=vnc-tls.o vnc-auth-vencrypt.o
 endif
@@ -174,9 +174,11 @@ sdl.o: sdl.c keymaps.h sdl_keysym.h
 
 sdl.o audio/sdlaudio.o: CFLAGS += $(SDL_CFLAGS)
 
+acl.o: acl.h acl.c
+
 vnc.h: vnc-tls.h vnc-auth-vencrypt.h vnc-auth-sasl.h keymaps.h
 
-vnc.o: vnc.c vnc.h vnc_keysym.h vnchextile.h d3des.c d3des.h
+vnc.o: vnc.c vnc.h vnc_keysym.h vnchextile.h d3des.c d3des.h acl.h
 
 vnc.o: CFLAGS += $(CONFIG_VNC_TLS_CFLAGS)
 

acl.c

+/*
+ * QEMU access control list management
+ *
+ * Copyright (C) 2009 Red Hat, Inc
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+
+#include "qemu-common.h"
+#include "sysemu.h"
+#include "acl.h"
+
+#ifdef HAVE_FNMATCH_H
+#include <fnmatch.h>
+#endif
+
+
+static unsigned int nacls = 0;
+static qemu_acl **acls = NULL;
+
+
+
+qemu_acl *qemu_acl_find(const char *aclname)
+{
+    int i;
+    for (i = 0 ; i < nacls ; i++) {
+	if (strcmp(acls[i]->aclname, aclname) == 0)
+	    return acls[i];
+    }
+
+    return NULL;
+}
+
+qemu_acl *qemu_acl_init(const char *aclname)
+{
+    qemu_acl *acl;
+
+    acl = qemu_acl_find(aclname);
+    if (acl)
+	return acl;
+
+    acl = qemu_malloc(sizeof(*acl));
+    acl->aclname = qemu_strdup(aclname);
+    /* Deny by default, so there is no window of "open
+     * access" between QEMU starting, and the user setting
+     * up ACLs in the monitor */
+    acl->defaultDeny = 1;
+
+    acl->nentries = 0;
+    TAILQ_INIT(&acl->entries);
+
+    acls = qemu_realloc(acls, sizeof(*acls) * (nacls +1));
+    acls[nacls] = acl;
+    nacls++;
+
+    return acl;
+}
+
+int qemu_acl_party_is_allowed(qemu_acl *acl,
+			      const char *party)
+{
+    qemu_acl_entry *entry;
+
+    TAILQ_FOREACH(entry, &acl->entries, next) {
+#ifdef HAVE_FNMATCH_H
+	if (fnmatch(entry->match, party, 0) == 0)
+	    return entry->deny ? 0 : 1;
+#else
+	/* No fnmatch, so fallback to exact string matching
+	 * instead of allowing wildcards */
+	if (strcmp(entry->match, party) == 0)
+	    return entry->deny ? 0 : 1;
+#endif
+    }
+
+    return acl->defaultDeny ? 0 : 1;
+}
+
+
+void qemu_acl_reset(qemu_acl *acl)
+{
+    qemu_acl_entry *entry;
+
+    /* Put back to deny by default, so there is no window
+     * of "open access" while the user re-initializes the
+     * access control list */
+    acl->defaultDeny = 1;
+    TAILQ_FOREACH(entry, &acl->entries, next) {
+	TAILQ_REMOVE(&acl->entries, entry, next);
+	free(entry->match);
+	free(entry);
+    }
+    acl->nentries = 0;
+}
+
+
+int qemu_acl_append(qemu_acl *acl,
+		    int deny,
+		    const char *match)
+{
+    qemu_acl_entry *entry;
+
+    entry = qemu_malloc(sizeof(*entry));
+    entry->match = qemu_strdup(match);
+    entry->deny = deny;
+
+    TAILQ_INSERT_TAIL(&acl->entries, entry, next);
+    acl->nentries++;
+
+    return acl->nentries;
+}
+
+
+int qemu_acl_insert(qemu_acl *acl,
+		    int deny,
+		    const char *match,
+		    int index)
+{
+    qemu_acl_entry *entry;
+    qemu_acl_entry *tmp;
+    int i = 0;
+
+    if (index <= 0)
+	return -1;
+    if (index >= acl->nentries)
+	return qemu_acl_append(acl, deny, match);
+
+
+    entry = qemu_malloc(sizeof(*entry));
+    entry->match = qemu_strdup(match);
+    entry->deny = deny;
+
+    TAILQ_FOREACH(tmp, &acl->entries, next) {
+	i++;
+	if (i == index) {
+	    TAILQ_INSERT_BEFORE(tmp, entry, next);
+	    acl->nentries++;
+	    break;
+	}
+    }
+
+    return i;
+}
+
+int qemu_acl_remove(qemu_acl *acl,
+		    const char *match)
+{
+    qemu_acl_entry *entry;
+    int i = 0;
+
+    TAILQ_FOREACH(entry, &acl->entries, next) {
+	i++;
+	if (strcmp(entry->match, match) == 0) {
+	    TAILQ_REMOVE(&acl->entries, entry, next);
+	    return i;
+	}
+    }
+    return -1;
+}
+
+
+/*
+ * Local variables:
+ *  c-indent-level: 4
+ *  c-basic-offset: 4
+ *  tab-width: 8
+ * End:
+ */

acl.h

+/*
+ * QEMU access control list management
+ *
+ * Copyright (C) 2009 Red Hat, Inc
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#ifndef __QEMU_ACL_H__
+#define __QEMU_ACL_H__
+
+#include "sys-queue.h"
+
+typedef struct qemu_acl_entry qemu_acl_entry;
+typedef struct qemu_acl qemu_acl;
+
+struct qemu_acl_entry {
+    char *match;
+    int deny;
+
+    TAILQ_ENTRY(qemu_acl_entry) next;
+};
+
+struct qemu_acl {
+    char *aclname;
+    unsigned int nentries;
+    TAILQ_HEAD(,qemu_acl_entry) entries;
+    int defaultDeny;
+};
+
+qemu_acl *qemu_acl_init(const char *aclname);
+
+qemu_acl *qemu_acl_find(const char *aclname);
+
+int qemu_acl_party_is_allowed(qemu_acl *acl,
+			      const char *party);
+
+void qemu_acl_reset(qemu_acl *acl);
+
+int qemu_acl_append(qemu_acl *acl,
+		    int deny,
+		    const char *match);
+int qemu_acl_insert(qemu_acl *acl,
+		    int deny,
+		    const char *match,
+		    int index);
+int qemu_acl_remove(qemu_acl *acl,
+		    const char *match);
+
+#endif /* __QEMU_ACL_H__ */
+
+/*
+ * Local variables:
+ *  c-indent-level: 4
+ *  c-basic-offset: 4
+ *  tab-width: 8
+ * End:
+ */

configure

@@ -861,6 +861,21 @@ EOF
     fi
 fi
 
+##########################################
+# fnmatch() probe, used for ACL routines
+fnmatch="no"
+cat > $TMPC << EOF
+#include <fnmatch.h>
+int main(void)
+{
+    fnmatch("foo", "foo", 0);
+    return 0;
+}
+EOF
+if $cc $ARCH_CFLAGS -o $TMPE $TMPC > /dev/null 2> /dev/null ; then
+   fnmatch="yes"
+fi
+
 ##########################################
 # vde libraries probe
 if test "$vde" = "yes" ; then
@@ -1421,6 +1436,9 @@ if test "$vnc_sasl" = "yes" ; then
   echo "CONFIG_VNC_SASL_LIBS=$vnc_sasl_libs" >> $config_mak
   echo "#define CONFIG_VNC_SASL 1" >> $config_h
 fi
+if test "$fnmatch" = "yes" ; then
+  echo "#define HAVE_FNMATCH_H 1" >> $config_h
+fi
 qemu_version=`head $source_path/VERSION`
 echo "VERSION=$qemu_version" >>$config_mak
 echo "#define QEMU_VERSION \"$qemu_version\"" >> $config_h

monitor.c

@@ -41,6 +41,7 @@
 #include "qemu-timer.h"
 #include "migration.h"
 #include "kvm.h"
+#include "acl.h"
 
 //#define DEBUG
 //#define DEBUG_COMPLETION
@@ -1532,6 +1533,86 @@ static void do_info_balloon(Monitor *mon)
         monitor_printf(mon, "balloon: actual=%d\n", (int)(actual >> 20));
 }
 
+static void do_acl(Monitor *mon,
+                   const char *command,
+		   const char *aclname,
+		   const char *match,
+		   int has_index,
+		   int index)
+{
+    qemu_acl *acl;
+
+    acl = qemu_acl_find(aclname);
+    if (!acl) {
+	monitor_printf(mon, "acl: unknown list '%s'\n", aclname);
+	return;
+    }
+
+    if (strcmp(command, "show") == 0) {
+	int i = 0;
+	qemu_acl_entry *entry;
+	monitor_printf(mon, "policy: %s\n",
+                       acl->defaultDeny ? "deny" : "allow");
+	TAILQ_FOREACH(entry, &acl->entries, next) {
+	    i++;
+	    monitor_printf(mon, "%d: %s %s\n", i,
+                           entry->deny ? "deny" : "allow",
+                           entry->match);
+	}
+    } else if (strcmp(command, "reset") == 0) {
+	qemu_acl_reset(acl);
+	monitor_printf(mon, "acl: removed all rules\n");
+    } else if (strcmp(command, "policy") == 0) {
+	if (!match) {
+	    monitor_printf(mon, "acl: missing policy parameter\n");
+	    return;
+	}
+
+	if (strcmp(match, "allow") == 0) {
+	    acl->defaultDeny = 0;
+	    monitor_printf(mon, "acl: policy set to 'allow'\n");
+	} else if (strcmp(match, "deny") == 0) {
+	    acl->defaultDeny = 1;
+	    monitor_printf(mon, "acl: policy set to 'deny'\n");
+	} else {
+	    monitor_printf(mon, "acl: unknown policy '%s', expected 'deny' or 'allow'\n", match);
+	}
+    } else if ((strcmp(command, "allow") == 0) ||
+	       (strcmp(command, "deny") == 0)) {
+	int deny = strcmp(command, "deny") == 0 ? 1 : 0;
+	int ret;
+
+	if (!match) {
+	    monitor_printf(mon, "acl: missing match parameter\n");
+	    return;
+	}
+
+	if (has_index)
+	    ret = qemu_acl_insert(acl, deny, match, index);
+	else
+	    ret = qemu_acl_append(acl, deny, match);
+	if (ret < 0)
+	    monitor_printf(mon, "acl: unable to add acl entry\n");
+	else
+	    monitor_printf(mon, "acl: added rule at position %d\n", ret);
+    } else if (strcmp(command, "remove") == 0) {
+	int ret;
+
+	if (!match) {
+	    monitor_printf(mon, "acl: missing match parameter\n");
+	    return;
+	}
+
+	ret = qemu_acl_remove(acl, match);
+	if (ret < 0)
+	    monitor_printf(mon, "acl: no matching acl entry\n");
+	else
+	    monitor_printf(mon, "acl: removed rule at position %d\n", ret);
+    } else {
+	monitor_printf(mon, "acl: unknown command '%s'\n", command);
+    }
+}
+
 /* Please update qemu-doc.texi when adding or changing commands */
 static const mon_cmd_t mon_cmds[] = {
     { "help|?", "s?", help_cmd,
@@ -1636,6 +1717,12 @@ static const mon_cmd_t mon_cmds[] = {
       "target", "request VM to change it's memory allocation (in MB)" },
     { "set_link", "ss", do_set_link,
       "name [up|down]", "change the link status of a network adapter" },
+    { "acl", "sss?i?", do_acl, "<command> <aclname> [<match>] [<index>]\n",
+                               "acl show vnc.username\n"
+                               "acl policy vnc.username deny\n"
+                               "acl allow vnc.username fred\n"
+                               "acl deny vnc.username bob\n"
+                               "acl reset vnc.username\n" },
     { NULL, NULL, },
 };
 
@@ -2961,6 +3048,15 @@ static void monitor_event(void *opaque, int event)
     }
 }
 
+
+/*
+ * Local variables:
+ *  c-indent-level: 4
+ *  c-basic-offset: 4
+ *  tab-width: 8
+ * End:
+ */
+
 void monitor_init(CharDriverState *chr, int flags)
 {
     static int is_first_init = 1;

qemu-doc.texi

@@ -631,6 +631,19 @@ ensures a data encryption preventing compromise of authentication
 credentials. See the @ref{vnc_security} section for details on using
 SASL authentication.
 
+@item acl
+
+Turn on access control lists for checking of the x509 client certificate
+and SASL party. For x509 certs, the ACL check is made against the
+certificate's distinguished name. This is something that looks like
+@code{C=GB,O=ACME,L=Boston,CN=bob}. For SASL party, the ACL check is
+made against the username, which depending on the SASL plugin, may
+include a realm component, eg @code{bob} or @code{bob\@EXAMPLE.COM}.
+When the @option{acl} flag is set, the initial access list will be
+empty, with a @code{deny} policy. Thus no one will be allowed to
+use the VNC server until the ACLs have been loaded. This can be
+achieved using the @code{acl} monitor command.
+
 @end table
 
 @end table
@@ -1392,6 +1405,42 @@ Password: ********
 
 @end table
 
+@item acl @var{subcommand} @var{aclname} @var{match} @var{index}
+
+Manage access control lists for network services. There are currently
+two named access control lists, @var{vnc.x509dname} and @var{vnc.username}
+matching on the x509 client certificate distinguished name, and SASL
+username respectively.
+
+@table @option
+@item acl show <aclname>
+list all the match rules in the access control list, and the default
+policy
+@item acl policy <aclname> @code{allow|deny}
+set the default access control list policy, used in the event that
+none of the explicit rules match. The default policy at startup is
+always @code{deny}
+@item acl allow <aclname> <match> [<index>]
+add a match to the access control list, allowing access. The match will
+normally be an exact username or x509 distinguished name, but can
+optionally include wildcard globs. eg @code{*\@EXAMPLE.COM} to allow
+all users in the @code{EXAMPLE.COM} kerberos realm. The match will
+normally be appended to the end of the ACL, but can be inserted
+earlier in the list if the optional @code{index} parameter is supplied.
+@item acl deny <aclname> <match> [<index>]
+add a match to the access control list, denying access. The match will
+normally be an exact username or x509 distinguished name, but can
+optionally include wildcard globs. eg @code{*\@EXAMPLE.COM} to allow
+all users in the @code{EXAMPLE.COM} kerberos realm. The match will
+normally be appended to the end of the ACL, but can be inserted
+earlier in the list if the optional @code{index} parameter is supplied.
+@item acl remove <aclname> <match>
+remove the specified match rule from the access control list.
+@item acl reset <aclname>
+remove all matches from the access control list, and set the default
+policy back to @code{deny}.
+@end table
+
 @item screendump @var{filename}
 Save screen into PPM image @var{filename}.
 

vnc-auth-sasl.c

@@ -120,22 +120,32 @@ static int vnc_auth_sasl_check_access(VncState *vs)
 {
     const void *val;
     int err;
+    int allow;
 
     err = sasl_getprop(vs->sasl.conn, SASL_USERNAME, &val);
     if (err != SASL_OK) {
-	VNC_DEBUG("cannot query SASL username on connection %d (%s)\n",
+	VNC_DEBUG("cannot query SASL username on connection %d (%s), denying access\n",
 		  err, sasl_errstring(err, NULL, NULL));
 	return -1;
     }
     if (val == NULL) {
-	VNC_DEBUG("no client username was found\n");
+	VNC_DEBUG("no client username was found, denying access\n");
 	return -1;
     }
     VNC_DEBUG("SASL client username %s\n", (const char *)val);
 
     vs->sasl.username = qemu_strdup((const char*)val);
 
-    return 0;
+    if (vs->vd->sasl.acl == NULL) {
+	VNC_DEBUG("no ACL activated, allowing access\n");
+	return 0;
+    }
+
+    allow = qemu_acl_party_is_allowed(vs->vd->sasl.acl, vs->sasl.username);
+
+    VNC_DEBUG("SASL client %s %s by ACL\n", vs->sasl.username,
+	      allow ? "allowed" : "denied");
+    return allow ? 0 : -1;
 }
 
 static int vnc_auth_sasl_check_ssf(VncState *vs)

vnc-auth-sasl.h

@@ -30,6 +30,9 @@
 #include <sasl/sasl.h>
 
 typedef struct VncStateSASL VncStateSASL;
+typedef struct VncDisplaySASL VncDisplaySASL;
+
+#include "acl.h"
 
 struct VncStateSASL {
     sasl_conn_t *conn;
@@ -56,6 +59,10 @@ struct VncStateSASL {
     char *mechlist;
 };
 
+struct VncDisplaySASL {
+    qemu_acl *acl;
+};
+
 void vnc_sasl_client_cleanup(VncState *vs);
 
 long vnc_client_read_sasl(VncState *vs);

vnc.c

@@ -28,6 +28,7 @@
 #include "sysemu.h"
 #include "qemu_socket.h"
 #include "qemu-timer.h"
+#include "acl.h"
 
 #define VNC_REFRESH_INTERVAL (1000 / 30)
 
@@ -2083,6 +2084,7 @@ int vnc_display_open(DisplayState *ds, const char *display)
     int sasl = 0;
     int saslErr;
 #endif
+    int acl = 0;
 
     if (!vnc_display)
         return -1;
@@ -2139,9 +2141,28 @@ int vnc_display_open(DisplayState *ds, const char *display)
 		return -1;
 	    }
 #endif
+	} else if (strncmp(options, "acl", 3) == 0) {
+	    acl = 1;
 	}
     }
 
+#ifdef CONFIG_VNC_TLS
+    if (acl && x509 && vs->tls.x509verify) {
+	if (!(vs->tls.acl = qemu_acl_init("vnc.x509dname"))) {
+	    fprintf(stderr, "Failed to create x509 dname ACL\n");
+	    exit(1);
+	}
+    }
+#endif
+#ifdef CONFIG_VNC_SASL
+    if (acl && sasl) {
+	if (!(vs->sasl.acl = qemu_acl_init("vnc.username"))) {
+	    fprintf(stderr, "Failed to create username ACL\n");
+	    exit(1);
+	}
+    }
+#endif
+
     /*
      * Combinations we support here:
      *

vnc.h

@@ -99,6 +99,9 @@ struct VncDisplay
     int subauth; /* Used by VeNCrypt */
     VncDisplayTLS tls;
 #endif
+#ifdef CONFIG_VNC_SASL
+    VncDisplaySASL sasl;
+#endif
 };
 
 struct VncState