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authorTom Gundersen <teg@jklm.no>2014-06-16 15:24:28 +0200
committerTom Gundersen <teg@jklm.no>2014-06-17 09:17:07 +0200
commit0bbc2c1f3b8f01eac7826dab1a3e1e073f63da8a (patch)
tree9d9d4b65918390369b38d95f34947c2a20a89842 /src/libsystemd-network
parent735a1a2ea5fb849e797c956bddf445a2a5bdf3d3 (diff)
sd-dhcp: checksum - make endianess-neutral
For efficiency, we group bytes together before adding them up. This is guaranteed to always work (regardless of the byte order) as long as the i-th byte in each group lign up with the i-th byte in each other group. On big-endian machines this broke when handling the trailing few bytes which did not make up a full group of 4 bytes. This patch fixes the problem by explicitly creating a 4 byte zero-padded group out of the trailing bytes. Reported and tested by Thomas Ritter <th.ritter@gmx.at>.
Diffstat (limited to 'src/libsystemd-network')
-rw-r--r--src/libsystemd-network/dhcp-internal.h2
-rw-r--r--src/libsystemd-network/dhcp-packet.c51
-rw-r--r--src/libsystemd-network/test-dhcp-client.c6
3 files changed, 22 insertions, 37 deletions
diff --git a/src/libsystemd-network/dhcp-internal.h b/src/libsystemd-network/dhcp-internal.h
index 76d357a6ed..03cc8243a9 100644
--- a/src/libsystemd-network/dhcp-internal.h
+++ b/src/libsystemd-network/dhcp-internal.h
@@ -48,7 +48,7 @@ int dhcp_option_parse(DHCPMessage *message, size_t len,
int dhcp_message_init(DHCPMessage *message, uint8_t op, uint32_t xid, uint8_t type,
size_t optlen, size_t *optoffset);
-uint16_t dhcp_packet_checksum(void *buf, size_t len);
+uint16_t dhcp_packet_checksum(uint8_t *buf, size_t len);
void dhcp_packet_append_ip_headers(DHCPPacket *packet, be32_t source_addr,
uint16_t source, be32_t destination_addr,
diff --git a/src/libsystemd-network/dhcp-packet.c b/src/libsystemd-network/dhcp-packet.c
index 3e2fb96c27..9f850fdebb 100644
--- a/src/libsystemd-network/dhcp-packet.c
+++ b/src/libsystemd-network/dhcp-packet.c
@@ -60,47 +60,32 @@ int dhcp_message_init(DHCPMessage *message, uint8_t op, uint32_t xid,
return 0;
}
-uint16_t dhcp_packet_checksum(void *buf, size_t len) {
- uint64_t *buf_64 = buf;
- uint64_t *end_64 = (uint64_t*)buf + (len / sizeof(uint64_t));
- uint32_t *buf_32;
- uint16_t *buf_16;
- uint8_t *buf_8;
+uint16_t dhcp_packet_checksum(uint8_t *buf, size_t len) {
+ uint64_t *buf_64 = (uint64_t*)buf;
+ uint64_t *end_64 = buf_64 + (len / sizeof(uint64_t));
uint64_t sum = 0;
+ /* See RFC1071 */
+
while (buf_64 < end_64) {
sum += *buf_64;
if (sum < *buf_64)
+ /* wrap around in one's complement */
sum++;
buf_64 ++;
}
- buf_32 = (uint32_t*)buf_64;
-
- if (len & sizeof(uint32_t)) {
- sum += *buf_32;
- if (sum < *buf_32)
- sum++;
-
- buf_32 ++;
- }
-
- buf_16 = (uint16_t*)buf_32;
-
- if (len & sizeof(uint16_t)) {
- sum += *buf_16;
- if (sum < *buf_16)
- sum ++;
-
- buf_16 ++;
- }
+ if (len % sizeof(uint64_t)) {
+ /* If the buffer is not aligned to 64-bit, we need
+ to zero-pad the last few bytes and add them in */
+ uint64_t buf_tail = 0;
- buf_8 = (uint8_t*)buf_16;
+ memcpy(&buf_tail, buf_64, len % sizeof(uint64_t));
- if (len & sizeof(uint8_t)) {
- sum += *buf_8;
- if (sum < *buf_8)
+ sum += buf_tail;
+ if (sum < buf_tail)
+ /* wrap around */
sum++;
}
@@ -129,11 +114,11 @@ void dhcp_packet_append_ip_headers(DHCPPacket *packet, be32_t source_addr,
packet->udp.len = htobe16(len - DHCP_IP_SIZE);
packet->ip.check = packet->udp.len;
- packet->udp.check = dhcp_packet_checksum(&packet->ip.ttl, len - 8);
+ packet->udp.check = dhcp_packet_checksum((uint8_t*)&packet->ip.ttl, len - 8);
packet->ip.ttl = IPDEFTTL;
packet->ip.check = 0;
- packet->ip.check = dhcp_packet_checksum(&packet->ip, DHCP_IP_SIZE);
+ packet->ip.check = dhcp_packet_checksum((uint8_t*)&packet->ip, DHCP_IP_SIZE);
}
int dhcp_packet_verify_headers(DHCPPacket *packet, size_t len, bool checksum) {
@@ -193,7 +178,7 @@ int dhcp_packet_verify_headers(DHCPPacket *packet, size_t len, bool checksum) {
if all the other checks have passed
*/
- if (dhcp_packet_checksum(&packet->ip, hdrlen)) {
+ if (dhcp_packet_checksum((uint8_t*)&packet->ip, hdrlen)) {
log_debug("ignoring packet: invalid IP checksum");
return -EINVAL;
}
@@ -202,7 +187,7 @@ int dhcp_packet_verify_headers(DHCPPacket *packet, size_t len, bool checksum) {
packet->ip.check = packet->udp.len;
packet->ip.ttl = 0;
- if (dhcp_packet_checksum(&packet->ip.ttl,
+ if (dhcp_packet_checksum((uint8_t*)&packet->ip.ttl,
be16toh(packet->udp.len) + 12)) {
log_debug("ignoring packet: invalid UDP checksum");
return -EINVAL;
diff --git a/src/libsystemd-network/test-dhcp-client.c b/src/libsystemd-network/test-dhcp-client.c
index 599bda1a5e..450b6d4d3c 100644
--- a/src/libsystemd-network/test-dhcp-client.c
+++ b/src/libsystemd-network/test-dhcp-client.c
@@ -128,7 +128,7 @@ static void test_checksum(void)
if (verbose)
printf("* %s\n", __FUNCTION__);
- assert_se(dhcp_packet_checksum(&buf, 20) == be16toh(0x78ae));
+ assert_se(dhcp_packet_checksum((uint8_t*)&buf, 20) == be16toh(0x78ae));
}
static int check_options(uint8_t code, uint8_t len, const uint8_t *option,
@@ -175,13 +175,13 @@ int dhcp_network_send_raw_socket(int s, const union sockaddr_union *link,
discover->ip.ttl = 0;
discover->ip.check = discover->udp.len;
- udp_check = ~dhcp_packet_checksum(&discover->ip.ttl, len - 8);
+ udp_check = ~dhcp_packet_checksum((uint8_t*)&discover->ip.ttl, len - 8);
assert_se(udp_check == 0xffff);
discover->ip.ttl = IPDEFTTL;
discover->ip.check = ip_check;
- ip_check = ~dhcp_packet_checksum(&discover->ip, sizeof(discover->ip));
+ ip_check = ~dhcp_packet_checksum((uint8_t*)&discover->ip, sizeof(discover->ip));
assert_se(ip_check == 0xffff);
assert_se(discover->dhcp.xid);