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[libvirt] [libvirt PATCHv5 1/2] add DHCP snooping



This patch adds DHCP Snooping support to libvirt.

Signed-off-by: David L Stevens <dlstevens us ibm com>
---
 docs/formatnwfilter.html.in              |   17 +
 examples/xml/nwfilter/no-ip-spoofing.xml |    5 +
 src/Makefile.am                          |    2 +
 src/nwfilter/nwfilter_dhcpsnoop.c        |  745 ++++++++++++++++++++++++++++++
 src/nwfilter/nwfilter_dhcpsnoop.h        |   38 ++
 src/nwfilter/nwfilter_driver.c           |    6 +
 src/nwfilter/nwfilter_gentech_driver.c   |   53 ++-
 7 files changed, 853 insertions(+), 13 deletions(-)
 create mode 100644 src/nwfilter/nwfilter_dhcpsnoop.c
 create mode 100644 src/nwfilter/nwfilter_dhcpsnoop.h

diff --git a/docs/formatnwfilter.html.in b/docs/formatnwfilter.html.in
index 8df4a93..8003320 100644
--- a/docs/formatnwfilter.html.in
+++ b/docs/formatnwfilter.html.in
@@ -1775,6 +1775,23 @@
        <br/><br/>
        In case a VM is resumed after suspension or migrated, IP address
        detection will be restarted.
+       <br/><br/>
+       Variable <i>ip_learning</i> may be used to specify
+       the IP address learning method. Valid values are <i>any</i>, <i>dhcp</i>,
+       or <i>none</i>. The default value is <i>any</i>, meaning that libvirt
+       may use any packet to determine the address in use by a VM. A value of
+       <i>dhcp</i> specifies that libvirt should only honor DHCP server-assigned
+       addresses with valid leases. If <i>ip_learning</i> is set to <i>none</i>,
+       libvirt does not do address learning and referencing <i>IP</i> without
+       assigning it an explicit value is an error.
+       <br/><br/>
+       Use of <i>ip_learning=dhcp</i> (DHCP snooping) provides additional
+       anti-spoofing security, especially when combined with a filter allowing
+       only trusted DHCP servers to assign addresses. If the DHCP lease expires,
+       the VM will no longer be able to use the IP address until it acquires a
+       new, valid lease from a DHCP server. If the VM is migrated, it must get
+       a new valid DHCP lease to use an IP address (e.g., by
+       bringing the VM interface down and up again).
      </p>
 
     <h3><a name="nwflimitsmigr">VM Migration</a></h3>
diff --git a/examples/xml/nwfilter/no-ip-spoofing.xml b/examples/xml/nwfilter/no-ip-spoofing.xml
index b8c94c8..7c7fd46 100644
--- a/examples/xml/nwfilter/no-ip-spoofing.xml
+++ b/examples/xml/nwfilter/no-ip-spoofing.xml
@@ -1,5 +1,10 @@
 <filter name='no-ip-spoofing' chain='ipv4'>
 
+    <!-- allow DHCP requests -->
+    <rule action='accept' direction='out'>
+        <ip match='yes' srcipaddr='0.0.0.0' protocol='udp' srcportstart='68'
+                  srcportend='68' />
+    </rule>
     <!-- drop if srcipaddr is not the IP address of the guest -->
     <rule action='drop' direction='out'>
         <ip match='no' srcipaddr='$IP' />
diff --git a/src/Makefile.am b/src/Makefile.am
index 87d91ed..c948cbf 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -481,6 +481,8 @@ NWFILTER_DRIVER_SOURCES =					\
 		nwfilter/nwfilter_driver.h nwfilter/nwfilter_driver.c	\
 		nwfilter/nwfilter_gentech_driver.c			\
 		nwfilter/nwfilter_gentech_driver.h			\
+		nwfilter/nwfilter_dhcpsnoop.c				\
+		nwfilter/nwfilter_dhcpsnoop.h				\
 		nwfilter/nwfilter_ebiptables_driver.c			\
 		nwfilter/nwfilter_ebiptables_driver.h			\
 		nwfilter/nwfilter_learnipaddr.c				\
diff --git a/src/nwfilter/nwfilter_dhcpsnoop.c b/src/nwfilter/nwfilter_dhcpsnoop.c
new file mode 100644
index 0000000..8a37a6f
--- /dev/null
+++ b/src/nwfilter/nwfilter_dhcpsnoop.c
@@ -0,0 +1,745 @@
+/*
+ * nwfilter_dhcpsnoop.c: support for DHCP snooping used by a VM
+ *                         on an interface
+ *
+ * Copyright (C) 2011 IBM Corp.
+ * Copyright (C) 2011 David L Stevens
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307  USA
+ *
+ * Author: David L Stevens <dlstevens us ibm com>
+ * Based in part on work by Stefan Berger <stefanb us ibm com>
+ */
+
+#include <config.h>
+
+#ifdef HAVE_LIBPCAP
+#include <pcap.h>
+#endif
+
+#include <fcntl.h>
+#include <sys/ioctl.h>
+#include <signal.h>
+
+#include <arpa/inet.h>
+#include <net/ethernet.h>
+#include <netinet/ip.h>
+#include <netinet/udp.h>
+#include <net/if.h>
+#include <net/if_arp.h>
+#include <intprops.h>
+
+#include "internal.h"
+
+#include "buf.h"
+#include "memory.h"
+#include "logging.h"
+#include "datatypes.h"
+#include "interface.h"
+#include "virterror_internal.h"
+#include "threads.h"
+#include "conf/nwfilter_params.h"
+#include "conf/domain_conf.h"
+#include "nwfilter_gentech_driver.h"
+#include "nwfilter_ebiptables_driver.h"
+#include "nwfilter_dhcpsnoop.h"
+
+#define VIR_FROM_THIS VIR_FROM_NWFILTER
+
+#ifdef HAVE_LIBPCAP
+
+static virHashTablePtr SnoopReqs;
+static pthread_mutex_t SnoopLock;
+
+#define snoop_lock()    { pthread_mutex_lock(&SnoopLock); }
+#define snoop_unlock()  { pthread_mutex_unlock(&SnoopLock); }
+
+struct virNWFilterSnoopReq {
+    virNWFilterTechDriverPtr  techdriver;
+    const char               *ifname;
+    int                       ifindex;
+    const char               *linkdev;
+    enum virDomainNetType     nettype;
+    unsigned char             macaddr[VIR_MAC_STRING_BUFLEN];
+    const char               *filtername;
+    virNWFilterHashTablePtr   vars;
+    virNWFilterDriverStatePtr driver;
+    /* start and end of lease list, ordered by lease time */
+    struct iplease           *start;
+    struct iplease           *end;
+    bool                      die;
+};
+
+#define POLL_INTERVAL    10*1000 /* 10 secs */
+
+struct iplease {
+    uint32_t                    ipl_ipaddr;
+    uint32_t                    ipl_server;
+    struct virNWFilterSnoopReq *ipl_req;
+    unsigned int                ipl_timeout;
+    /* timer list */
+    struct iplease             *ipl_prev;
+    struct iplease             *ipl_next;
+};
+
+static struct iplease *ipl_getbyip(struct iplease *start, uint32_t ipaddr);
+static void ipl_update(struct iplease *pl, uint32_t timeout);
+
+
+/*
+ * ipl_ladd - add an IP lease to a list
+ */
+static void
+ipl_ladd(struct iplease *plnew, struct iplease **start, struct iplease **end)
+{
+    struct iplease             *pl;
+
+    plnew->ipl_next = plnew->ipl_prev = 0;
+    if (!*start) {
+        *start = *end = plnew;
+        return;
+    }
+    for (pl = *end; pl && plnew->ipl_timeout < pl->ipl_timeout;
+         pl = pl->ipl_prev)
+        /* empty */ ;
+    if (!pl) {
+        plnew->ipl_next = *start;
+        *start = plnew;
+    } else {
+        plnew->ipl_next = pl->ipl_next;
+        pl->ipl_next = plnew;
+    }
+    plnew->ipl_prev = pl;
+    if (plnew->ipl_next)
+        plnew->ipl_next->ipl_prev = plnew;
+    else
+        *end = plnew;
+}
+
+/*
+ * ipl_tadd - add an IP lease to the timer list
+ */
+static void
+ipl_tadd(struct iplease *plnew)
+{
+    struct virNWFilterSnoopReq *req = plnew->ipl_req;
+
+    ipl_ladd(plnew, &req->start, &req->end);
+}
+ 
+/*
+ * ipl_install - install rule for a lease
+ */
+static int
+ipl_install(struct iplease *ipl)
+{
+    char            ipbuf[20];             /* dotted decimal IP addr string */
+    char           *ipstr;
+    int             rc;
+
+    if (!inet_ntop(AF_INET, &ipl->ipl_ipaddr, ipbuf, sizeof(ipbuf))) {
+        virNWFilterReportError(VIR_ERR_INTERNAL_ERROR,
+                               _("ipl_install inet_ntop " "failed (0x%08X)"),
+                               ipl->ipl_ipaddr);
+        return -1;
+    }
+
+    ipstr = strdup(ipbuf);
+    if (!ipstr) {
+        virReportOOMError();
+        return -1;
+    }
+    if (virNWFilterHashTablePut(ipl->ipl_req->vars, "IP", ipstr, 1)) {
+        virNWFilterReportError(VIR_ERR_INTERNAL_ERROR,
+                               _("Could not add variable \"IP\" to hashmap"));
+        VIR_FREE(ipstr);
+        return -1;
+    }
+    rc = virNWFilterInstantiateFilterLate(NULL,
+                                          ipl->ipl_req->ifname,
+                                          ipl->ipl_req->ifindex,
+                                          ipl->ipl_req->linkdev,
+                                          ipl->ipl_req->nettype,
+                                          ipl->ipl_req->macaddr,
+                                          ipl->ipl_req->filtername,
+                                          ipl->ipl_req->vars,
+                                          ipl->ipl_req->driver);
+    if (rc) {
+        VIR_FREE(ipstr);
+        return -1;
+    }
+    return 0;
+}
+
+/*
+ * ipl_add - create or update an IP lease
+ */
+static void
+ipl_add(struct iplease *plnew)
+{
+    struct iplease *pl;
+    struct virNWFilterSnoopReq *req = plnew->ipl_req;
+
+    pl = ipl_getbyip(req->start, plnew->ipl_ipaddr);
+    if (pl) {
+        ipl_update(pl, plnew->ipl_timeout);
+        return;
+    }
+    /* support for multiple addresses requires the ability to add filters
+     * to existing chains, or to instantiate address lists via
+     * virNWFilterInstantiateFilterLate(). Until one of those capabilities
+     * is added, don't allow a new address when one is already assigned to
+     * this interface.
+     */
+    if (req->start)
+         return;    /* silently ignore multiple addresses */
+
+    if (VIR_ALLOC(pl) < 0) {
+        virReportOOMError();
+        return;
+    }
+    *pl = *plnew;
+
+    if (ipl_install(pl) < 0) {
+        VIR_FREE(pl);
+        return;
+    }
+    ipl_tadd(pl);
+}
+
+/*
+ * ipl_tdel - remove an IP lease from a list
+ */
+static void
+ipl_ldel(struct iplease *ipl, struct iplease **start, struct iplease **end)
+{
+    if (ipl->ipl_prev)
+        ipl->ipl_prev->ipl_next = ipl->ipl_next;
+    else
+        *start = ipl->ipl_next;
+    if (ipl->ipl_next)
+        ipl->ipl_next->ipl_prev = ipl->ipl_prev;
+    else
+        *end = ipl->ipl_prev;
+    ipl->ipl_next = ipl->ipl_prev = 0;
+}
+
+/*
+ * ipl_tdel - remove an IP lease from the timer list
+ */
+static void
+ipl_tdel(struct iplease *ipl)
+{
+    struct virNWFilterSnoopReq *req = ipl->ipl_req;
+
+    ipl_ldel(ipl, &req->start, &req->end);
+    ipl->ipl_timeout = 0;
+}
+
+/*
+ * ipl_del - delete an IP lease
+ */
+static void
+ipl_del(struct virNWFilterSnoopReq *req, uint32_t ipaddr)
+{
+    struct iplease *ipl;
+
+    ipl = ipl_getbyip(req->start, ipaddr);
+    if (ipl == NULL)
+        return;
+
+    ipl_tdel(ipl);
+
+    /* for multiple address support, this needs to remove those rules
+     * referencing "IP" with ipl's ip value.
+     */
+    if (req->techdriver->applyDHCPOnlyRules(req->ifname, req->macaddr, NULL)) {
+        virNWFilterReportError(VIR_ERR_INTERNAL_ERROR, "ipl_ldel failed");
+    }
+    VIR_FREE(ipl);
+}
+
+/*
+ * ipl_update - update the timeout on an IP lease
+ */
+static void
+ipl_update(struct iplease *ipl, uint32_t timeout)
+{
+    if (timeout < ipl->ipl_timeout)
+        return;  /* no take-backs */
+    ipl_tdel(ipl);
+    ipl->ipl_timeout = timeout;
+    ipl_tadd(ipl);
+    return;
+}
+
+/*
+ * ipl_getbyip - lookup IP lease by IP address
+ */
+static struct iplease *
+ipl_getbyip(struct iplease *start, uint32_t ipaddr)
+{
+    struct iplease *pl;
+
+    for (pl = start; pl && pl->ipl_ipaddr != ipaddr; pl = pl->ipl_next)
+        /* empty */ ;
+    return pl;
+}
+
+/*
+ * ipl_trun - run the IP lease timeout list
+ */
+static unsigned int
+ipl_trun(struct virNWFilterSnoopReq *req)
+{
+    uint32_t now;
+
+    now = time(0);
+    while (req->start && req->start->ipl_timeout <= now)
+        ipl_del(req, req->start->ipl_ipaddr);
+    return 0;
+}
+
+typedef unsigned char Eaddr[6];
+
+struct eth {
+    Eaddr eh_dst;
+    Eaddr eh_src;
+    unsigned short eh_type;
+    union {
+        unsigned char eu_data[0];
+        struct vlan_hdr {
+            unsigned short ev_flags;
+            unsigned short ev_type;
+            unsigned char  ev_data[0];
+        } eu_vlh;
+    } eth_un;
+} ATTRIBUTE_PACKED;
+
+#define eh_data eth_un.eu_data
+#define ehv_data eth_un.eu_vlh.ev_data
+#define ehv_type eth_un.eu_vlh.ev_type
+
+struct dhcp {
+    unsigned char  d_op;
+    unsigned char  d_htype;
+    unsigned char  d_hlen;
+    unsigned char  d_hops;
+    unsigned int   d_xid;
+    unsigned short d_secs;
+    unsigned short d_flags;
+    unsigned int   d_ciaddr;
+    unsigned int   d_yiaddr;
+    unsigned int   d_siaddr;
+    unsigned int   d_giaddr;
+    unsigned char  d_chaddr[16];
+    char           d_sname[64];
+    char           d_file[128];
+    unsigned char  d_opts[0];
+};
+
+/* DHCP options */
+
+#define DHCPO_PAD         0
+#define DHCPO_LEASE      51     /* lease time in secs */
+#define DHCPO_MTYPE      53     /* message type */
+#define DHCPO_END       255     /* end of options */
+
+/* DHCP message types */
+#define DHCPDECLINE     4
+#define DHCPACK         5
+#define DHCPRELEASE     7
+
+unsigned char dhcp_magic[4] = { 99, 130, 83, 99 };
+
+static int
+dhcp_getopt(struct dhcp *pd, int len, int *pmtype, int *pleasetime)
+{
+    int oind, olen;
+    int oend;
+
+    olen = len - sizeof *pd;
+    oind = 0;
+
+    if (olen < 4)               /* bad magic */
+        return -1;
+    if (memcmp(dhcp_magic, pd->d_opts, sizeof dhcp_magic) != 0)
+        return -1;              /* bad magic */
+    oind += sizeof dhcp_magic;
+
+    oend = 0;
+
+    *pmtype = *pleasetime = 0;
+
+    while (oind < olen) {
+        switch (pd->d_opts[oind]) {
+            case DHCPO_LEASE:
+                if (olen - oind < 6)
+                    goto malformed;
+                if (*pleasetime)
+                    return -1;  /* duplicate lease time */
+                *pleasetime =
+                    ntohl(*(unsigned int *) (pd->d_opts + oind + 2));
+                break;
+            case DHCPO_MTYPE:
+                if (olen - oind < 3)
+                    goto malformed;
+                if (*pmtype)
+                    return -1;  /* duplicate message type */
+                *pmtype = pd->d_opts[oind + 2];
+                break;
+            case DHCPO_PAD:
+                oind++;
+                continue;
+
+            case DHCPO_END:
+                oend = 1;
+                break;
+            default:
+                if (olen - oind < 2)
+                    goto malformed;
+        }
+        if (oend)
+            break;
+        oind += pd->d_opts[oind + 1] + 2;
+    }
+    return 0;
+  malformed:
+    VIR_WARN("got lost in the options!");
+    return -1;
+}
+
+static void
+dhcpdecode(struct virNWFilterSnoopReq *req, struct eth *pep, int len)
+{
+    struct iphdr   *pip;
+    struct udphdr  *pup;
+    struct dhcp    *pd;
+    struct iplease  ipl;
+    int             mtype, leasetime;
+
+    /* go through the protocol headers */
+    switch (ntohs(pep->eh_type)) {
+    case ETHERTYPE_IP:
+        pip = (struct iphdr *) pep->eh_data;
+        len -= offsetof(struct eth, eh_data);
+        break;
+    case ETHERTYPE_VLAN:
+        if (ntohs(pep->ehv_type) != ETHERTYPE_IP)
+            return;
+        pip = (struct iphdr *) pep->ehv_data;
+        len -= offsetof(struct eth, ehv_data);
+        break;
+    default:
+        return;
+    }
+    pip = (struct iphdr *) pep->eh_data;
+    len -= sizeof(*pep);
+    pup = (struct udphdr *) ((char *) pip + (pip->ihl << 2));
+    len -= pip->ihl << 2;
+    pd = (struct dhcp *) ((char *) pup + sizeof(*pup));
+    len -= sizeof(*pup);
+    if (len < 0)
+        return;                 /* dhcpdecode: invalid packet length */
+    if (dhcp_getopt(pd, len, &mtype, &leasetime) < 0)
+        return;
+
+    memset(&ipl, 0, sizeof(ipl));
+    ipl.ipl_ipaddr = pd->d_yiaddr;
+    ipl.ipl_server = pd->d_siaddr;
+    if (leasetime == ~0)
+        ipl.ipl_timeout = ~0;
+    else
+        ipl.ipl_timeout = time(0) + leasetime;
+    ipl.ipl_req = req;
+
+    switch (mtype) {
+        case DHCPACK:
+            ipl_add(&ipl);
+            break;
+        case DHCPDECLINE:
+        case DHCPRELEASE:
+            ipl_del(req, ipl.ipl_ipaddr);
+            break;
+        default:
+            break;
+    }
+}
+
+#define PBUFSIZE        576     /* >= IP/TCP/DHCP headers */
+
+static pcap_t *
+dhcpopen(const char *intf)
+{
+    pcap_t             *handle;
+    struct bpf_program  fp;
+    char                filter[64];
+    char                pcap_errbuf[PCAP_ERRBUF_SIZE];
+
+    handle = pcap_open_live(intf, PBUFSIZE, 0, POLL_INTERVAL, pcap_errbuf);
+    if (handle == NULL) {
+        virNWFilterReportError(VIR_ERR_INTERNAL_ERROR,
+                               _("pcap_open_live: %s"), pcap_errbuf);
+        return 0;
+    }
+
+    sprintf(filter, "port 67 or dst port 68");
+    if (pcap_compile(handle, &fp, filter, 1, PCAP_NETMASK_UNKNOWN) != 0) {
+        virNWFilterReportError(VIR_ERR_INTERNAL_ERROR,
+                               _("pcap_compile: %s"), pcap_geterr(handle));
+        return 0;
+    }
+    if (pcap_setfilter(handle, &fp) != 0) {
+        virNWFilterReportError(VIR_ERR_INTERNAL_ERROR,
+                               _("pcap_setfilter: %s"), pcap_geterr(handle));
+        return 0;
+    }
+    pcap_freecode(&fp);
+    return handle;
+}
+
+static void
+snoopReqFree(struct virNWFilterSnoopReq *req)
+{
+    struct iplease *ipl;
+
+    if (!req)
+        return;
+
+    /* free all leases */
+    snoop_lock();
+    for (ipl = req->start; ipl; ipl = req->start)
+        ipl_del(req, ipl->ipl_ipaddr);
+    snoop_unlock();
+
+    /* free all req data */
+    VIR_FREE(req->ifname);
+    VIR_FREE(req->linkdev);
+    VIR_FREE(req->filtername);
+    virNWFilterHashTableFree(req->vars);
+    VIR_FREE(req);
+}
+
+static void *
+virNWFilterDHCPSnoop(void *req0)
+{
+    struct virNWFilterSnoopReq *req = req0;
+    pcap_t                     *handle;
+    struct pcap_pkthdr          hdr;
+    struct eth                 *packet;
+    int                         ifindex;
+
+    handle = dhcpopen(req->ifname);
+    if (!handle)
+        return 0;
+
+    ifindex = if_nametoindex(req->ifname);
+
+    while (1) {
+        if (req->die)
+            break;
+        snoop_lock();
+        ipl_trun(req);
+        snoop_unlock();
+
+        packet = (struct eth *) pcap_next(handle, &hdr);
+
+        if (!packet) {
+            if (ifaceCheck(false, req->ifname, NULL, ifindex))
+                virNWFilterDHCPSnoopEnd(req->ifname);
+            continue;
+        }
+
+        snoop_lock();
+        dhcpdecode(req, packet, hdr.caplen);
+        snoop_unlock();
+    }
+    snoopReqFree(req);
+    return 0;
+}
+
+int
+virNWFilterDHCPSnoopReq(virNWFilterTechDriverPtr techdriver,
+                        const char *ifname,
+                        int ifindex,
+                        const char *linkdev,
+                        enum virDomainNetType nettype,
+                        const unsigned char *macaddr,
+                        const char *filtername,
+                        virNWFilterHashTablePtr filterparams,
+                        virNWFilterDriverStatePtr driver)
+{
+    struct virNWFilterSnoopReq *req;
+    pthread_t                   thread;
+
+    snoop_lock();
+    req = virHashLookup(SnoopReqs, ifname);
+    snoop_unlock();
+    if (req)
+        return 0;
+
+    if (VIR_ALLOC(req) < 0) {
+        virReportOOMError();
+        return 1;
+    }
+
+    req->ifname = strdup(ifname);
+    if (req->ifname == NULL) {
+        snoopReqFree(req);
+        virReportOOMError();
+        return 1;
+    }
+
+    req->techdriver = techdriver;
+    req->ifindex = ifindex;
+    req->linkdev = linkdev ? strdup(linkdev) : NULL;
+    req->nettype = nettype;
+    memcpy(req->macaddr, macaddr, sizeof(req->macaddr));
+    req->filtername = strdup(filtername);
+    if (req->filtername == NULL) {
+        snoopReqFree(req);
+        virReportOOMError();
+        return 1;
+    }
+
+    if (techdriver->applyDHCPOnlyRules(req->ifname, req->macaddr, NULL)) {
+        virNWFilterReportError(VIR_ERR_INTERNAL_ERROR, "applyDHCPOnlyRules "
+                               "failed - spoofing not protected!");
+    }
+
+    req->vars = virNWFilterHashTableCreate(0);
+    if (!req->vars) {
+        snoopReqFree(req);
+        virReportOOMError();
+        return 1;
+    }
+    if (virNWFilterHashTablePutAll(filterparams, req->vars)) {
+        virNWFilterReportError(VIR_ERR_INTERNAL_ERROR,
+                               _("virNWFilterDHCPSnoopReq: can't copy variables"
+                                " on if %s"), ifname);
+        snoopReqFree(req);
+        return 1;
+    }
+    req->driver = driver;
+
+    snoop_lock();
+    if (virHashAddEntry(SnoopReqs, ifname, req)) {
+        snoop_unlock();
+        virNWFilterReportError(VIR_ERR_INTERNAL_ERROR,
+                               _("virNWFilterDHCPSnoopReq req add failed on "
+                                "interface \"%s\""), ifname);
+        snoopReqFree(req);
+        return 1;
+    }
+    snoop_unlock();
+    if (pthread_create(&thread, NULL, virNWFilterDHCPSnoop, req) != 0) {
+        (void) virHashRemoveEntry(SnoopReqs, ifname);
+        snoopReqFree(req);
+        virNWFilterReportError(VIR_ERR_INTERNAL_ERROR,
+                               _("virNWFilterDHCPSnoopReq pthread_create failed"
+                                " on interface \"%s\""), ifname);
+        return 1;
+    }
+    return 0;
+}
+
+/*
+ * freeReq - hash table free function to kill a request
+ */
+static void
+freeReq(void *req0, const void *name ATTRIBUTE_UNUSED)
+{
+    struct virNWFilterSnoopReq *req = (struct virNWFilterSnoopReq *) req0;
+
+    if (!req)
+        return;
+
+    req->die = 1;
+}
+
+int
+virNWFilterDHCPSnoopInit(void)
+{
+    if (SnoopReqs)
+        return 0;
+
+    if (pthread_mutex_init(&SnoopLock, 0) < 0) {
+        virNWFilterReportError(VIR_ERR_INTERNAL_ERROR,
+                               _("pthread_mutex_init: %s"), strerror(errno));
+        return -1;
+    }
+    snoop_lock();
+    SnoopReqs = virHashCreate(0, freeReq);
+    if (!SnoopReqs) {
+        snoop_unlock();
+        virReportOOMError();
+        return -1;
+    }
+    snoop_unlock();
+    return 0;
+}
+
+void
+virNWFilterDHCPSnoopEnd(const char *ifname)
+{
+    snoop_lock();
+    if (!SnoopReqs) {
+        snoop_unlock();
+        return;
+    }
+    if (ifname)
+        virHashRemoveEntry(SnoopReqs, ifname);
+    else {                      /* free all of them */
+        virHashFree(SnoopReqs);
+        SnoopReqs = virHashCreate(0, freeReq);
+        if (!SnoopReqs) {
+            snoop_unlock();
+            virReportOOMError();
+            return;
+        }
+    }
+    snoop_unlock();
+}
+
+#else /* HAVE_LIBPCAP */
+int
+virNWFilterDHCPSnoopInit(void)
+{
+    return -1;
+}
+
+void
+virNWFilterDHCPSnoopEnd(const char *ifname ATTRIBUTE_UNUSED)
+{
+    return;
+}
+
+int
+virNWFilterDHCPSnoopReq(virNWFilterTechDriverPtr techdriver ATTRIBUTE_UNUSED,
+                        const char *ifname ATTRIBUTE_UNUSED,
+                        int ifindex ATTRIBUTE_UNUSED,
+                        const char *linkdev ATTRIBUTE_UNUSED,
+                        enum virDomainNetType nettype ATTRIBUTE_UNUSED,
+                        const unsigned char *macaddr ATTRIBUTE_UNUSED,
+                        const char *filtername ATTRIBUTE_UNUSED,
+                        virNWFilterHashTablePtr filterparams ATTRIBUTE_UNUSED,
+                        virNWFilterDriverStatePtr driver ATTRIBUTE_UNUSED)
+{
+    virNWFilterReportError(VIR_ERR_INTERNAL_ERROR, _("libvirt was not compiled "
+                           "with libpcap and \"ip_learning='dhcp'\" requires"
+                           " it."));
+    return 1;
+}
+#endif /* HAVE_LIBPCAP */
diff --git a/src/nwfilter/nwfilter_dhcpsnoop.h b/src/nwfilter/nwfilter_dhcpsnoop.h
new file mode 100644
index 0000000..94762d1
--- /dev/null
+++ b/src/nwfilter/nwfilter_dhcpsnoop.h
@@ -0,0 +1,38 @@
+/*
+ * nwfilter_dhcpsnoop.h: support DHCP snooping for a VM on an interface
+ *
+ * Copyright (C) 2010 IBM Corp.
+ * Copyright (C) 2010 David L Stevens
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307  USA
+ *
+ * Author: David L Stevens <dlstevens us ibm com>
+ */
+
+#ifndef __NWFILTER_DHCPSNOOP_H
+#define __NWFILTER_DHCPSNOOP_H
+
+int virNWFilterDHCPSnoopInit(void);
+int virNWFilterDHCPSnoopReq(virNWFilterTechDriverPtr techdriver,
+                            const char *ifname,
+                            int ifindex,
+                            const char *linkdev,
+                            enum virDomainNetType nettype,
+                            const unsigned char *macaddr,
+                            const char *filtername,
+                            virNWFilterHashTablePtr filterparams,
+                            virNWFilterDriverStatePtr driver);
+void virNWFilterDHCPSnoopEnd(const char *ifname);
+#endif /* __NWFILTER_DHCPSNOOP_H */
diff --git a/src/nwfilter/nwfilter_driver.c b/src/nwfilter/nwfilter_driver.c
index a735059..b877d9d 100644
--- a/src/nwfilter/nwfilter_driver.c
+++ b/src/nwfilter/nwfilter_driver.c
@@ -39,6 +39,7 @@
 #include "nwfilter_gentech_driver.h"
 #include "configmake.h"
 
+#include "nwfilter_dhcpsnoop.h"
 #include "nwfilter_learnipaddr.h"
 
 #define VIR_FROM_THIS VIR_FROM_NWFILTER
@@ -66,6 +67,8 @@ static int
 nwfilterDriverStartup(int privileged) {
     char *base = NULL;
 
+    if (virNWFilterDHCPSnoopInit() < 0)
+        return -1;
     if (virNWFilterLearnInit() < 0)
         return -1;
 
@@ -127,6 +130,7 @@ alloc_err_exit:
 
 conf_init_err:
     virNWFilterTechDriversShutdown();
+    virNWFilterDHCPSnoopEnd(0);
     virNWFilterLearnShutdown();
 
     return -1;
@@ -149,6 +153,7 @@ nwfilterDriverReload(void) {
     conn = virConnectOpen("qemu:///system");
 
     if (conn) {
+        virNWFilterDHCPSnoopEnd(0);
         /* shut down all threads -- they will be restarted if necessary */
         virNWFilterLearnThreadsTerminate(true);
 
@@ -201,6 +206,7 @@ nwfilterDriverShutdown(void) {
 
     virNWFilterConfLayerShutdown();
     virNWFilterTechDriversShutdown();
+    virNWFilterDHCPSnoopEnd(0);
     virNWFilterLearnShutdown();
 
     nwfilterDriverLock(driverState);
diff --git a/src/nwfilter/nwfilter_gentech_driver.c b/src/nwfilter/nwfilter_gentech_driver.c
index 7891983..2b10f9b 100644
--- a/src/nwfilter/nwfilter_gentech_driver.c
+++ b/src/nwfilter/nwfilter_gentech_driver.c
@@ -33,6 +33,7 @@
 #include "virterror_internal.h"
 #include "nwfilter_gentech_driver.h"
 #include "nwfilter_ebiptables_driver.h"
+#include "nwfilter_dhcpsnoop.h"
 #include "nwfilter_learnipaddr.h"
 
 
@@ -42,6 +43,8 @@
 #define NWFILTER_STD_VAR_MAC "MAC"
 #define NWFILTER_STD_VAR_IP  "IP"
 
+#define NWFILTER_DFLT_LEARN  "any"
+
 static int _virNWFilterTeardownFilter(const char *ifname);
 
 
@@ -638,6 +641,8 @@ virNWFilterInstantiate(virConnectPtr conn,
     void **ptrs = NULL;
     int instantiate = 1;
     char *buf;
+    const char *learning;
+    bool reportIP = false;
 
     virNWFilterHashTablePtr missing_vars = virNWFilterHashTableCreate(0);
     if (!missing_vars) {
@@ -655,22 +660,42 @@ virNWFilterInstantiate(virConnectPtr conn,
     if (rc)
         goto err_exit;
 
+    learning = virHashLookup(vars->hashTable, "ip_learning");
+    if (learning == NULL)
+        learning = NWFILTER_DFLT_LEARN;
+
     if (virHashSize(missing_vars->hashTable) == 1) {
         if (virHashLookup(missing_vars->hashTable,
                           NWFILTER_STD_VAR_IP) != NULL) {
-            if (virNWFilterLookupLearnReq(ifindex) == NULL) {
-                rc = virNWFilterLearnIPAddress(techdriver,
-                                               ifname,
-                                               ifindex,
-                                               linkdev,
-                                               nettype, macaddr,
-                                               filter->name,
-                                               vars, driver,
-                                               DETECT_DHCP|DETECT_STATIC);
+            if (c_strcasecmp(learning, "none") == 0) {        /* no learning */
+                reportIP = true;
+                goto err_unresolvable_vars;
             }
-            goto err_exit;
-        }
-        goto err_unresolvable_vars;
+            if (c_strcasecmp(learning, "dhcp") == 0) {
+                rc = virNWFilterDHCPSnoopReq(techdriver, ifname, ifindex,
+                                             linkdev, nettype, macaddr,
+                                             filter->name, vars, driver);
+                goto err_exit;
+            } else if (c_strcasecmp(learning, "any") == 0) {
+                if (virNWFilterLookupLearnReq(ifindex) == NULL) {
+                    rc = virNWFilterLearnIPAddress(techdriver,
+                                                   ifname,
+                                                   ifindex,
+                                                   linkdev,
+                                                   nettype, macaddr,
+                                                   filter->name,
+                                                   vars, driver,
+                                                   DETECT_DHCP|DETECT_STATIC);
+                }
+                goto err_exit;
+            } else {
+                rc = 1;
+                virNWFilterReportError(VIR_ERR_PARSE_FAILED, _("filter '%s' "
+                                       "learning value '%s' invalid."),
+                                       filter->name, learning);
+            }
+        } else
+             goto err_unresolvable_vars;
     } else if (virHashSize(missing_vars->hashTable) > 1) {
         goto err_unresolvable_vars;
     } else if (!forceWithPendingReq &&
@@ -738,7 +763,7 @@ err_exit:
 
 err_unresolvable_vars:
 
-    buf = virNWFilterPrintVars(missing_vars->hashTable, ", ", false, false);
+    buf = virNWFilterPrintVars(missing_vars->hashTable, ", ", false, reportIP);
     if (buf) {
         virNWFilterReportError(VIR_ERR_INTERNAL_ERROR,
                    _("Cannot instantiate filter due to unresolvable "
@@ -1070,6 +1095,8 @@ _virNWFilterTeardownFilter(const char *ifname)
         return 1;
     }
 
+    virNWFilterDHCPSnoopEnd(ifname);
+
     virNWFilterTerminateLearnReq(ifname);
 
     if (virNWFilterLockIface(ifname))
-- 
1.7.6.4


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