On Fri, Apr 09, 2010 at 02:57:43PM -0400, Stefan Berger wrote:
> I mistakenly took the op field in the DHCP message as the DHCP_OFFER
> type. Rather than basing the decision to read the VM's IP address on
> that field, process the appended DHCP options where option 53 indicates
> the actual type of the packet. I am also reading the broadcast address
> of the VM, but don't use it so far.
>
> Signed-off-by: Stefan Berger <stefanb@xxxxxxxxxx>
>
> ---
> src/nwfilter/nwfilter_learnipaddr.c | 61 +++++++++++++++++++++++++++++++++---
> 1 file changed, 56 insertions(+), 5 deletions(-)
>
> Index: libvirt-acl/src/nwfilter/nwfilter_learnipaddr.c
> ===================================================================
> --- libvirt-acl.orig/src/nwfilter/nwfilter_learnipaddr.c
> +++ libvirt-acl/src/nwfilter/nwfilter_learnipaddr.c
> @@ -64,6 +64,13 @@ struct f_arphdr {
> } ATTRIBUTE_PACKED;
>
>
> +struct dhcp_option {
> + uint8_t code;
> + uint8_t len;
> + uint8_t value[0]; /* length varies */
> +} ATTRIBUTE_PACKED;
> +
> +
> /* structure representing DHCP message */
> struct dhcp {
> uint8_t op;
> @@ -78,9 +85,12 @@ struct dhcp {
> uint32_t siaddr;
> uint32_t giaddr;
> uint8_t chaddr[16];
> - /* omitted */
> + uint8_t zeroes[192];
> + uint32_t magic;
> + struct dhcp_option options[0];
> } ATTRIBUTE_PACKED;
>
> +#define DHCP_MSGT_DHCPOFFER 2
>
> struct ether_vlan_header
> {
> @@ -212,6 +222,40 @@ virNWFilterGetIpAddrForIfname(const char
>
> #ifdef HAVE_LIBPCAP
>
> +static void
> +procDHCPOpts(struct dhcp *dhcp, int dhcp_opts_len,
> + uint32_t *vmaddr, uint32_t *bcastaddr,
> + enum howDetect *howDetected) {
> + struct dhcp_option *dhcpopt = &dhcp->options[0];
> +
> + while (dhcp_opts_len >= 2) {
> +
> + switch (dhcpopt->code) {
> +
> + case 28: /* Broadcast address */
> + if (dhcp_opts_len >= 6) {
> + uint32_t *tmp = (uint32_t *)&dhcpopt->value;
> + (*bcastaddr) = ntohl(*tmp);
> + }
> + break;
> +
> + case 53: /* Message type */
> + if (dhcp_opts_len >= 3) {
> + uint8_t *val = (uint8_t *)&dhcpopt->value;
> + switch (*val) {
> + case DHCP_MSGT_DHCPOFFER:
> + *vmaddr = dhcp->yiaddr;
> + *howDetected = DETECT_DHCP;
> + break;
> + }
> + }
> + }
> + dhcp_opts_len -= (2 + dhcpopt->len);
> + dhcpopt = (struct dhcp_option*)((char *)dhcpopt + 2 + dhcpopt->len);
> + }
> +}
> +
> +
> /**
> * learnIPAddressThread
> * arg: pointer to virNWFilterIPAddrLearnReq structure
> @@ -236,12 +280,13 @@ learnIPAddressThread(void *arg)
> struct ether_header *ether_hdr;
> struct ether_vlan_header *vlan_hdr;
> virNWFilterIPAddrLearnReqPtr req = arg;
> - uint32_t vmaddr = 0;
> + uint32_t vmaddr = 0, bcastaddr = 0;
> unsigned int ethHdrSize;
> char *listen_if = (strlen(req->linkdev) != 0) ? req->linkdev
> : req->ifname;
> int to_ms = (strlen(req->linkdev) != 0) ? 1000
> : 0;
> + int dhcp_opts_len;
> char macaddr[VIR_MAC_STRING_BUFLEN];
> virBuffer buf = VIR_BUFFER_INITIALIZER;
> char *filter= NULL;
> @@ -382,12 +427,18 @@ learnIPAddressThread(void *arg)
> sizeof(struct dhcp)) {
> struct dhcp *dhcp = (struct dhcp *)
> ((char *)udphdr + sizeof(udphdr));
> - if (dhcp->op == 2 /* DHCP OFFER */ &&
> + if (dhcp->op == 2 /* BOOTREPLY */ &&
> !memcmp(&dhcp->chaddr[0],
> req->macaddr,
> 6)) {
> - vmaddr = dhcp->yiaddr;
> - howDetected = DETECT_DHCP;
> + dhcp_opts_len = header.len -
> + (ethHdrSize + iphdr->ihl * 4 +
> + sizeof(struct udphdr) +
> + sizeof(struct dhcp));
> + procDHCPOpts(dhcp, dhcp_opts_len,
> + &vmaddr,
> + &bcastaddr,
> + &howDetected);
> }
> }
> }
>
>
Okay, it's a bit annoying to have to gather all those protocol
frame format within libvirt, but that's the simpler concerning the
specific usage.
Code looks okay,
ACK
Daniel
--
Daniel Veillard | libxml Gnome XML XSLT toolkit http://xmlsoft.org/
daniel@xxxxxxxxxxxx | Rpmfind RPM search engine http://rpmfind.net/
http://veillard.com/ | virtualization library http://libvirt.org/
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