50 lines
2.0 KiB
Diff
50 lines
2.0 KiB
Diff
From 7eed119b84b0f7efb7ef351940dd895dc2379eb3 Mon Sep 17 00:00:00 2001
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From: Russell Senior <russell@personaltelco.net>
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Date: Mon, 15 Mar 2021 23:27:58 -0700
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Subject: [PATCH v2] udhcpc: ignore zero-length DHCP options
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Discovered that the DHCP server on a TrendNet router (unknown model)
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provides a zero-length option 12 (Host Name) in the DHCP ACK message. This
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has the effect of causing udhcpc to drop the rest of the options, including
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option 51 (IP Address Lease Time), 3 (Router), and 6 (Domain Name Server),
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most importantly leaving the OpenWrt device with no default gateway.
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The TrendNet behavior violates RFC 2132, which in Section 3.14 declares that
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option 12 has a miniumum length of 1 octet. It is perhaps not a cosmic coincidence
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that I found this behavior on Pi Day.
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This patch allows zero length options without bailing out, by simply skipping them.
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v2 changelog:
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* advance the optionptr by two bytes, not one;
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* add a message to warn about the rfc violation;
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Signed-off-by: Russell Senior <russell@personaltelco.net>
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---
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networking/udhcp/common.c | 9 +++++++--
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1 file changed, 7 insertions(+), 2 deletions(-)
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diff --git a/networking/udhcp/common.c b/networking/udhcp/common.c
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index 4bc719001..a16fd85d0 100644
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--- a/networking/udhcp/common.c
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+++ b/networking/udhcp/common.c
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@@ -277,8 +277,13 @@ uint8_t* FAST_FUNC udhcp_scan_options(struct dhcp_packet *packet, struct dhcp_sc
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goto complain; /* complain and return NULL */
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len = 2 + scan_state->optionptr[OPT_LEN];
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scan_state->rem -= len;
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- /* So far no valid option with length 0 known. */
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- if (scan_state->rem < 0 || scan_state->optionptr[OPT_LEN] == 0)
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+ /* skip any options with zero length */
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+ if (scan_state->optionptr[OPT_LEN] == 0) {
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+ scan_state->optionptr += 2;
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+ bb_simple_error_msg("warning: zero length DHCP option violates rfc2132, skipping");
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+ continue;
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+ }
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+ if (scan_state->rem < 0)
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goto complain; /* complain and return NULL */
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if (scan_state->optionptr[OPT_CODE] == DHCP_OPTION_OVERLOAD) {
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--
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2.30.1
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