dhcpv4: fix padding of iovec message in dhcpv4_handle_msg()

Fix the FIXME added earlier by calculating the length of the iovec package and
adding padding as necessary to comply with the BOOTP specification (which
defines the minimum length of a message as 300 bytes).

Signed-off-by: David Härdeman <[email protected]>
Link: https://github.com/openwrt/odhcpd/pull/278
Signed-off-by: Álvaro Fernández Rojas <[email protected]>

diff --git a/src/dhcpv4.c b/src/dhcpv4.c
index 8d127e060b0d4abf8de99c3623f013f5d2c59205..30df7abf978112c8636a6c145f7428819e3ec03b 100644 (file)
--- a/src/dhcpv4.c
+++ b/src/dhcpv4.c
@@ -154,6 +154,25 @@ static void dhcpv4_put(struct dhcpv4_message *msg, uint8_t **cursor,
        memcpy(c, data, len);
 }
 
+static void dhcpv4_add_padding(struct iovec *iov, size_t iovlen)
+{
+       // Theoretical max padding = vendor-specific area, RFC951, §3
+       static uint8_t padding[64] = { 0 };
+       size_t len = 0;
+
+       if (!iov || !iovlen)
+               return;
+
+       iov[iovlen - 1].iov_base = padding;
+       iov[iovlen - 1].iov_len = 0;
+
+       for (size_t i = 0; i < iovlen; i++)
+               len += iov[i].iov_len;
+
+       if (len < DHCPV4_MIN_PACKET_SIZE)
+               iov[iovlen - 1].iov_len = DHCPV4_MIN_PACKET_SIZE - len;
+}
+
 static void dhcpv4_fr_send(struct dhcp_assignment *a)
 {
        struct dhcpv4_message fr_msg = {
@@ -644,6 +663,7 @@ enum {
        IOV_DNR,
        IOV_DNR_BODY,
        IOV_END,
+       IOV_PADDING,
        IOV_TOTAL
 };
 
@@ -779,6 +799,7 @@ void dhcpv4_handle_msg(void *src_addr, void *data, size_t len,
                [IOV_DNR]               = { &reply_dnr, 0 },
                [IOV_DNR_BODY]          = { NULL, 0 },
                [IOV_END]               = { &reply_end, sizeof(reply_end) },
+               [IOV_PADDING]           = { NULL, 0 },
        };
 
        /* Misc */
@@ -1153,10 +1174,8 @@ void dhcpv4_handle_msg(void *src_addr, void *data, size_t len,
                reply.yiaddr.s_addr = a->addr;
 
        memcpy(reply.chaddr, req->chaddr, sizeof(reply.chaddr));
-
        dhcpv4_set_dest_addr(iface, reply_msg.data, req, &reply, src_addr, &dest_addr);
-
-       /* FIXME: check for DHCPV4_MIN_PACKET_SIZE */
+       dhcpv4_add_padding(iov, ARRAY_SIZE(iov));
 
        if (send_reply(iov, ARRAY_SIZE(iov), (struct sockaddr *)&dest_addr, sizeof(dest_addr), opaque) < 0)
                error("Failed to send %s to %s - %s: %m",