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libsystemd-network: fix endianness in ARP BPF filter (#8255)

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Commit f11cba7479 ("libsystemd-network: fix unaligned loads (issue #7654)")
changed the way in which the MAC address is read to use native endiannes:

 htobe32(*((uint32_t *)x)  ->  unaligned_read_ne32(x)

This is wrong because loads done with BPF_LD + BPF_ABS are big-endian, as it
can be seen for the ethertype and arp-operation loads above in the
filter.  Also, the same commit changed:

 htobe32(*((unsigned int *)x) -> unaligned_read_be32(x)

in _bind_raw_socket(), which is the correct form.

The commit broke IPv4LL in presence of loops, as the sender now considers its
own packets as conflicting.

Fixes: f11cba7479
This commit is contained in:
Beniamino Galvani 2018-02-22 18:09:33 +01:00 committed by Lennart Poettering
parent d156d1d2c9
commit 6afe9046d5
1 changed files with 2 additions and 2 deletions
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4
src/libsystemd-network/arp-util.c
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@ -49,12 +49,12 @@ int arp_network_bind_raw_socket(int ifindex, be32_t address, const struct ether_
BPF_JUMP(BPF_JMP + BPF_JEQ + BPF_K, ARPOP_REPLY, 1, 0), /* protocol == reply ? */
BPF_STMT(BPF_RET + BPF_K, 0), /* ignore */
/* Sender Hardware Address must be different from our own */
BPF_STMT(BPF_LD + BPF_IMM, unaligned_read_ne32(&eth_mac->ether_addr_octet[0])),/* A <- 4 bytes of client's MAC */
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_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_K, 0, 0, 6), /* A == 0 ? */
BPF_STMT(BPF_LD + BPF_IMM, unaligned_read_ne16(&eth_mac->ether_addr_octet[4])),/* A <- 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_ALU + BPF_XOR + BPF_X, 0), /* A xor X */