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udhcpc: make DHCP packets to have at least 300 DHCP bytes

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Commit b8b72f02 removed all padding from DHCP packets
to fix operation with buggy servers which can't handle
maximum sized packets.  But it introduced a regression
with buggy routers which drop DHCP packets smaller
than 300 bytes (i.e. 342 byte ethernet packets).
Add back some padding to work around.

function                                             old     new   delta
udhcp_send_kernel_packet                             268     292     +24
udhcp_send_raw_packet                                462     473     +11
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 2/0 up/down: 35/0)               Total: 35 bytes

Signed-off-by: Johannes Stezenbach <js@sig21.net>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Johannes Stezenbach 2013-10-28 23:27:37 +01:00 committed by Denys Vlasenko
parent af4f0e48ec
commit 2d576e2a22
1 changed files with 9 additions and 0 deletions
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9
networking/udhcp/packet.c
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@ -143,8 +143,15 @@ int FAST_FUNC udhcp_send_raw_packet(struct dhcp_packet *dhcp_pkt,
*
* In order to work with those buggy servers,
* we truncate packets after end option byte.
*
* However, RFC 1542 says "The IP Total Length and UDP Length
* must be large enough to contain the minimal BOOTP header of 300 octets".
* Thus, we retain enough padding to not go below 300 BOOTP bytes.
* Some devices have filters which drop DHCP packets shorter than that.
*/
padding = DHCP_OPTIONS_BUFSIZE - 1 - udhcp_end_option(packet.data.options);
if (padding > DHCP_SIZE - 300)
padding = DHCP_SIZE - 300;
packet.ip.protocol = IPPROTO_UDP;
packet.ip.saddr = source_nip;
@ -215,6 +222,8 @@ int FAST_FUNC udhcp_send_kernel_packet(struct dhcp_packet *dhcp_pkt,
udhcp_dump_packet(dhcp_pkt);
padding = DHCP_OPTIONS_BUFSIZE - 1 - udhcp_end_option(dhcp_pkt->options);
if (padding > DHCP_SIZE - 300)
padding = DHCP_SIZE - 300;
result = safe_write(fd, dhcp_pkt, DHCP_SIZE - padding);
msg = "write";
ret_close: