From 0c6a3c888abd720b5ab28162d1ba4eadffde5272 Mon Sep 17 00:00:00 2001 From: Patrik Flykt Date: Fri, 20 Dec 2013 17:16:15 +0200 Subject: libsystemd-dhcp: Fix checksum computation for buffer with odd size Fix off-by-one error and notice that summing may need more than one round for the result to be in the lower 16 bits. --- src/libsystemd-dhcp/dhcp-client.c | 7 +++++-- src/libsystemd-dhcp/test-dhcp-client.c | 7 +++++-- 2 files changed, 10 insertions(+), 4 deletions(-) (limited to 'src/libsystemd-dhcp') diff --git a/src/libsystemd-dhcp/dhcp-client.c b/src/libsystemd-dhcp/dhcp-client.c index 7dc1546128..68a3b1a1b6 100644 --- a/src/libsystemd-dhcp/dhcp-client.c +++ b/src/libsystemd-dhcp/dhcp-client.c @@ -382,10 +382,13 @@ static uint16_t client_checksum(void *buf, int len) if (len & 0x01) { odd = buf; - sum += odd[len]; + sum += odd[len - 1]; } - return ~((sum & 0xffff) + (sum >> 16)); + while (sum >> 16) + sum = (sum & 0xffff) + (sum >> 16); + + return ~sum; } static void client_append_ip_headers(DHCPPacket *packet, uint16_t len) diff --git a/src/libsystemd-dhcp/test-dhcp-client.c b/src/libsystemd-dhcp/test-dhcp-client.c index d398510745..7400cc6837 100644 --- a/src/libsystemd-dhcp/test-dhcp-client.c +++ b/src/libsystemd-dhcp/test-dhcp-client.c @@ -102,10 +102,13 @@ static uint16_t client_checksum(void *buf, int len) if (len & 0x01) { odd = buf; - sum += odd[len]; + sum += odd[len - 1]; } - return ~((sum & 0xffff) + (sum >> 16)); + while (sum >> 16) + sum = (sum & 0xffff) + (sum >> 16); + + return ~sum; } static void test_checksum(void) -- cgit v1.2.3-54-g00ecf