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busybox: udhcpc, allow zero length dhcp options

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This patch skips zero length DHCP options instead of failing.

Signed-off-by: Russell Senior <russell@personaltelco.net>
This commit is contained in:
Russell Senior 2021-03-16 01:24:18 -07:00 committed by Hauke Mehrtens
parent 410fb05b44
commit 1c04365071
1 changed files with 49 additions and 0 deletions
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49
package/utils/busybox/patches/205-udhcpc_allow_zero_length_options.patch Normal file
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@ -0,0 +1,49 @@
From 7eed119b84b0f7efb7ef351940dd895dc2379eb3 Mon Sep 17 00:00:00 2001
From: Russell Senior <russell@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 <russell@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