Discovered that the DHCP server on a TrendNet router (unknown model) provides a zero-length option 12 (Host Name) in the DHCP ACK message. This has the effect of causing udhcpc to drop the rest of the options, including option 51 (IP Address Lease Time), 3 (Router), and 6 (Domain Name Server), most importantly leaving the OpenWrt device with no default gateway.
The TrendNet behavior violates RFC 2132, which in Section 3.14 declares that option 12 has a miniumum length of 1 octet. It is perhaps not a cosmic coincidence that I found this behavior on Pi Day. This patch allows zero length options without bailing out, by simply skipping them. v2 changelog: * advance the optionptr by two bytes, not one; * add a message to warn about the rfc violation; Signed-off-by: Russell Senior <[email protected]> --- networking/udhcp/common.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/networking/udhcp/common.c b/networking/udhcp/common.c index 4bc719001..a16fd85d0 100644 --- a/networking/udhcp/common.c +++ b/networking/udhcp/common.c @@ -277,8 +277,13 @@ uint8_t* FAST_FUNC udhcp_scan_options(struct dhcp_packet *packet, struct dhcp_sc goto complain; /* complain and return NULL */ len = 2 + scan_state->optionptr[OPT_LEN]; scan_state->rem -= len; - /* So far no valid option with length 0 known. */ - if (scan_state->rem < 0 || scan_state->optionptr[OPT_LEN] == 0) + /* skip any options with zero length */ + if (scan_state->optionptr[OPT_LEN] == 0) { + scan_state->optionptr += 2; + bb_simple_error_msg("warning: zero length DHCP option violates rfc2132, skipping"); + continue; + } + if (scan_state->rem < 0) goto complain; /* complain and return NULL */ if (scan_state->optionptr[OPT_CODE] == DHCP_OPTION_OVERLOAD) { -- 2.30.1 -- Russell Senior, President [email protected] _______________________________________________ busybox mailing list [email protected] http://lists.busybox.net/mailman/listinfo/busybox
