This patch skips zero length DHCP options instead of failing.
v2 changelog: * fix off-by-one * add a warning message * move commit message into patch sent upstream Signed-off-by: Russell Senior <russ...@personaltelco.net> --- ...205-udhcpc_allow_zero_length_options.patch | 49 +++++++++++++++++++ 1 file changed, 49 insertions(+) create mode 100644 package/utils/busybox/patches/205-udhcpc_allow_zero_length_options.patch diff --git a/package/utils/busybox/patches/205-udhcpc_allow_zero_length_options.patch b/package/utils/busybox/patches/205-udhcpc_allow_zero_length_options.patch new file mode 100644 index 0000000000..abe8baf54f --- /dev/null +++ b/package/utils/busybox/patches/205-udhcpc_allow_zero_length_options.patch @@ -0,0 +1,49 @@ +From 7eed119b84b0f7efb7ef351940dd895dc2379eb3 Mon Sep 17 00:00:00 2001 +From: Russell Senior <russ...@personaltelco.net> +Date: Mon, 15 Mar 2021 23:27:58 -0700 +Subject: [PATCH v2] udhcpc: ignore zero-length DHCP options + +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 <russ...@personaltelco.net> +--- + 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 + -- 2.30.1 -- Russell Senior, President russ...@personaltelco.net _______________________________________________ openwrt-devel mailing list openwrt-devel@lists.openwrt.org https://lists.openwrt.org/mailman/listinfo/openwrt-devel