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sd-dhcp-client: use BPF on raw socket

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Filter out everything except UDP packets destined for the DHCP client port,
this should avoid the vast majority of spurious wakeups.

Filter based on [0], with permission.

Possible improvemnts: also check for the DHCP magic cookie to drop invalid
packets. Check for our xid to filter out packets destined for other clients.

[0]: <https://github.com/ambrop72/badvpn/blob/master/dhcpclient/BDHCPClient.c#L57>
This commit is contained in:
Tom Gundersen 2014-03-31 09:54:18 +02:00
parent b6b20d1d36
commit bc29e507e2
1 changed files with 18 additions and 0 deletions
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18
src/libsystemd-network/dhcp-network.c
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@ -25,6 +25,7 @@
#include <net/ethernet.h>
#include <stdio.h>
#include <unistd.h>
#include <linux/filter.h>
#include "socket-util.h"
@ -32,6 +33,19 @@
int dhcp_network_bind_raw_socket(int index, union sockaddr_union *link)
{
struct sock_filter filter[] = {
BPF_STMT(BPF_LD + BPF_B + BPF_ABS, offsetof(DHCPPacket, ip.protocol)), /* A <- IP protocol */
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, IPPROTO_UDP, 1, 0), /* IP protocol = UDP? */
BPF_STMT(BPF_RET + BPF_K, 0), /* ignore */
BPF_STMT(BPF_LD + BPF_H + BPF_ABS, offsetof(DHCPPacket, udp.dest)), /* A <- UDP destination port */
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, DHCP_PORT_CLIENT, 1, 0), /* UDP destination port = DHCP client? */
BPF_STMT(BPF_RET + BPF_K, 0), /* ignore */
BPF_STMT(BPF_RET + BPF_K, 65535), /* return all */
};
struct sock_fprog fprog = {
.len = ELEMENTSOF(filter),
.filter = filter
};
int s, one = 1;
assert(index > 0);
@ -50,6 +64,10 @@ int dhcp_network_bind_raw_socket(int index, union sockaddr_union *link)
if (setsockopt (s, SOL_PACKET, PACKET_AUXDATA, &one, sizeof(one)) < 0)
return -errno;
if (setsockopt(s, SOL_SOCKET, SO_ATTACH_FILTER, &fprog, sizeof(fprog)) < 0) {
return -errno;
}
if (bind(s, &link->sa, sizeof(link->ll)) < 0) {
safe_close(s);
return -errno;