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arp-util: shorten BPF code a bit

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- replace `A = k` and `X = A` with `X = k`,
- replace `A ^= X` and `A == 0` with `A == X`.
- use UINT32_MAX when accept a packet
This commit is contained in:
Yu Watanabe 2021-10-19 20:05:11 +09:00
parent 21f2b19cc2
commit e2c7c38b74
2 changed files with 16 additions and 23 deletions
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35
src/libsystemd-network/arp-util.c
View File

@ -14,7 +14,7 @@
#include "unaligned.h" #include "unaligned.h"
#include "util.h" #include "util.h"
int arp_update_filter(int fd, const struct in_addr *a, const struct ether_addr *eth_mac) { int arp_update_filter(int fd, const struct in_addr *a, const struct ether_addr *mac) {
struct sock_filter filter[] = { struct sock_filter filter[] = {
BPF_STMT(BPF_LD + BPF_W + BPF_LEN, 0), /* A <- packet length */ BPF_STMT(BPF_LD + BPF_W + BPF_LEN, 0), /* A <- packet length */
BPF_JUMP(BPF_JMP + BPF_JGE + BPF_K, sizeof(struct ether_arp), 1, 0), /* packet >= arp packet ? */ BPF_JUMP(BPF_JMP + BPF_JGE + BPF_K, sizeof(struct ether_arp), 1, 0), /* packet >= arp packet ? */
@ -36,30 +36,22 @@ int arp_update_filter(int fd, const struct in_addr *a, const struct ether_addr *
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ARPOP_REPLY, 1, 0), /* protocol == reply ? */ BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ARPOP_REPLY, 1, 0), /* protocol == reply ? */
BPF_STMT(BPF_RET + BPF_K, 0), /* ignore */ BPF_STMT(BPF_RET + BPF_K, 0), /* ignore */
/* Sender Hardware Address must be different from our own */ /* Sender Hardware Address must be different from our own */
BPF_STMT(BPF_LD + BPF_IMM, unaligned_read_be32(&eth_mac->ether_addr_octet[0])),/* A <- 4 bytes of client's MAC */ BPF_STMT(BPF_LDX + BPF_IMM, unaligned_read_be32(&mac->ether_addr_octet[0])), /* X <- 4 bytes of client's MAC */
BPF_STMT(BPF_MISC + BPF_TAX, 0), /* X <- A */
BPF_STMT(BPF_LD + BPF_W + BPF_ABS, offsetof(struct ether_arp, arp_sha)), /* A <- 4 bytes of SHA */ BPF_STMT(BPF_LD + BPF_W + BPF_ABS, offsetof(struct ether_arp, arp_sha)), /* A <- 4 bytes of SHA */
BPF_STMT(BPF_ALU + BPF_XOR + BPF_X, 0), /* A xor X */ BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_X, 0, 0, 4), /* A == X ? */
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0, 0, 6), /* A == 0 ? */ BPF_STMT(BPF_LDX + BPF_IMM, unaligned_read_be16(&mac->ether_addr_octet[4])), /* X <- remainder of client's MAC */
BPF_STMT(BPF_LD + BPF_IMM, unaligned_read_be16(&eth_mac->ether_addr_octet[4])),/* A <- remainder of client's MAC */
BPF_STMT(BPF_MISC + BPF_TAX, 0), /* X <- A */
BPF_STMT(BPF_LD + BPF_H + BPF_ABS, offsetof(struct ether_arp, arp_sha) + 4), /* A <- remainder of SHA */ BPF_STMT(BPF_LD + BPF_H + BPF_ABS, offsetof(struct ether_arp, arp_sha) + 4), /* A <- remainder of SHA */
BPF_STMT(BPF_ALU + BPF_XOR + BPF_X, 0), /* A xor X */ BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_X, 0, 0, 1), /* A == X ? */
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0, 0, 1), /* A == 0 ? */
BPF_STMT(BPF_RET + BPF_K, 0), /* ignore */ BPF_STMT(BPF_RET + BPF_K, 0), /* ignore */
/* Sender Protocol Address or Target Protocol Address must be equal to the one we care about */ /* Sender Protocol Address or Target Protocol Address must be equal to the one we care about */
BPF_STMT(BPF_LD + BPF_IMM, htobe32(a->s_addr)), /* A <- clients IP */ BPF_STMT(BPF_LDX + BPF_IMM, htobe32(a->s_addr)), /* X <- clients IP */
BPF_STMT(BPF_MISC + BPF_TAX, 0), /* X <- A */
BPF_STMT(BPF_LD + BPF_W + BPF_ABS, offsetof(struct ether_arp, arp_spa)), /* A <- SPA */ BPF_STMT(BPF_LD + BPF_W + BPF_ABS, offsetof(struct ether_arp, arp_spa)), /* A <- SPA */
BPF_STMT(BPF_ALU + BPF_XOR + BPF_X, 0), /* X xor A */ BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_X, 0, 0, 1), /* A == X ? */
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0, 0, 1), /* A == 0 ? */ BPF_STMT(BPF_RET + BPF_K, UINT32_MAX), /* accept */
BPF_STMT(BPF_RET + BPF_K, 65535), /* return all */ BPF_STMT(BPF_LDX + BPF_IMM, htobe32(a->s_addr)), /* A <- clients IP */
BPF_STMT(BPF_LD + BPF_IMM, htobe32(a->s_addr)), /* A <- clients IP */
BPF_STMT(BPF_MISC + BPF_TAX, 0), /* X <- A */
BPF_STMT(BPF_LD + BPF_W + BPF_ABS, offsetof(struct ether_arp, arp_tpa)), /* A <- TPA */ BPF_STMT(BPF_LD + BPF_W + BPF_ABS, offsetof(struct ether_arp, arp_tpa)), /* A <- TPA */
BPF_STMT(BPF_ALU + BPF_XOR + BPF_X, 0), /* X xor A */ BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_X, 0, 0, 1), /* A == 0 ? */
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0, 0, 1), /* A == 0 ? */ BPF_STMT(BPF_RET + BPF_K, UINT32_MAX), /* accept */
BPF_STMT(BPF_RET + BPF_K, 65535), /* return all */
BPF_STMT(BPF_RET + BPF_K, 0), /* ignore */ BPF_STMT(BPF_RET + BPF_K, 0), /* ignore */
}; };
struct sock_fprog fprog = { struct sock_fprog fprog = {
@ -75,7 +67,7 @@ int arp_update_filter(int fd, const struct in_addr *a, const struct ether_addr *
return 0; return 0;
} }
int arp_network_bind_raw_socket(int ifindex, const struct in_addr *a, const struct ether_addr *eth_mac) { int arp_network_bind_raw_socket(int ifindex, const struct in_addr *a, const struct ether_addr *mac) {
union sockaddr_union link = { union sockaddr_union link = {
.ll.sll_family = AF_PACKET, .ll.sll_family = AF_PACKET,
.ll.sll_protocol = htobe16(ETH_P_ARP), .ll.sll_protocol = htobe16(ETH_P_ARP),
@ -87,12 +79,13 @@ int arp_network_bind_raw_socket(int ifindex, const struct in_addr *a, const stru
int r; int r;
assert(ifindex > 0); assert(ifindex > 0);
assert(mac);
s = socket(AF_PACKET, SOCK_DGRAM | SOCK_CLOEXEC | SOCK_NONBLOCK, 0); s = socket(AF_PACKET, SOCK_DGRAM | SOCK_CLOEXEC | SOCK_NONBLOCK, 0);
if (s < 0) if (s < 0)
return -errno; return -errno;
r = arp_update_filter(s, a, eth_mac); r = arp_update_filter(s, a, mac);
if (r < 0) if (r < 0)
return r; return r;

4
src/libsystemd-network/arp-util.h
View File

@ -11,8 +11,8 @@
#include "socket-util.h" #include "socket-util.h"
#include "sparse-endian.h" #include "sparse-endian.h"
int arp_update_filter(int fd, const struct in_addr *a, const struct ether_addr *eth_mac); int arp_update_filter(int fd, const struct in_addr *a, const struct ether_addr *mac);
int arp_network_bind_raw_socket(int ifindex, const struct in_addr *a, const struct ether_addr *eth_mac); int arp_network_bind_raw_socket(int ifindex, const struct in_addr *a, const struct ether_addr *mac);
int arp_send_packet( int arp_send_packet(
int fd, int fd,