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dhcp: 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 20:28:57 +09:00
parent 155943b259
commit ea51deb188
1 changed files with 6 additions and 10 deletions
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16
src/libsystemd-network/dhcp-network.c
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@ -58,24 +58,20 @@ static int _bind_raw_socket(int ifindex, union sockaddr_union *link,
/* We only support MAC address length to be either 0 or 6 (ETH_ALEN). Optionally
* compare chaddr for ETH_ALEN bytes. */
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETH_ALEN, 0, 12), /* A (the MAC address length) == ETH_ALEN ? */
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_MISC + BPF_TAX, 0), /* X <- A */
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ETH_ALEN, 0, 8), /* A (the MAC address length) == ETH_ALEN ? */
BPF_STMT(BPF_LDX + BPF_IMM, unaligned_read_be32(&eth_mac->ether_addr_octet[0])), /* X <- 4 bytes of client's MAC */
BPF_STMT(BPF_LD + BPF_W + BPF_ABS, offsetof(DHCPPacket, dhcp.chaddr)), /* A <- 4 bytes of MAC from dhcp.chaddr */
BPF_STMT(BPF_ALU + BPF_XOR + BPF_X, 0), /* A xor X */
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0, 1, 0), /* A == 0 ? */
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_X, 0, 1, 0), /* A == X ? */
BPF_STMT(BPF_RET + BPF_K, 0), /* ignore */
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_LDX + BPF_IMM, unaligned_read_be16(&eth_mac->ether_addr_octet[4])), /* X <- remainder of client's MAC */
BPF_STMT(BPF_LD + BPF_H + BPF_ABS, offsetof(DHCPPacket, dhcp.chaddr) + 4), /* A <- remainder of MAC from dhcp.chaddr */
BPF_STMT(BPF_ALU + BPF_XOR + BPF_X, 0), /* A xor X */
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, 0, 1, 0), /* A == 0 ? */
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_X, 0, 1, 0), /* A == X ? */
BPF_STMT(BPF_RET + BPF_K, 0), /* ignore */
BPF_STMT(BPF_LD + BPF_W + BPF_ABS, offsetof(DHCPPacket, dhcp.magic)), /* A <- DHCP magic cookie */
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, DHCP_MAGIC_COOKIE, 1, 0), /* cookie == DHCP magic cookie ? */
BPF_STMT(BPF_RET + BPF_K, 0), /* ignore */
BPF_STMT(BPF_RET + BPF_K, 65535), /* return all */
BPF_STMT(BPF_RET + BPF_K, UINT32_MAX), /* accept */
};
struct sock_fprog fprog = {
.len = ELEMENTSOF(filter),