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+From 6d3b4bb24da9a07c263f3c1acf8df85382ff562c Mon Sep 17 00:00:00 2001
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+From: Denys Vlasenko <vda.linux@googlemail.com>
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+Date: Mon, 17 Dec 2018 18:07:18 +0100
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+Subject: [PATCH] udhcpc: check that 4-byte options are indeed 4-byte, closes
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+ 11506
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+
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+function old new delta
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+udhcp_get_option32 - 27 +27
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+udhcp_get_option 231 248 +17
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+------------------------------------------------------------------------------
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+(add/remove: 1/0 grow/shrink: 1/0 up/down: 44/0) Total: 44 bytes
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+
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+Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
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+
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+Upstream-Status: Backport
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+CVE: CVE-2018-20679
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+
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+Affects < 1.30.0
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+
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+signed-off-by: Armin Kuster <akuster@mvista.com>
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+
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+---
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+ networking/udhcp/common.c | 19 +++++++++++++++++++
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+ networking/udhcp/common.h | 4 ++++
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+ networking/udhcp/dhcpc.c | 6 +++---
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+ networking/udhcp/dhcpd.c | 6 +++---
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+ 4 files changed, 29 insertions(+), 6 deletions(-)
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+
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+Index: busybox-1.29.3/networking/udhcp/common.c
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+===================================================================
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+--- busybox-1.29.3.orig/networking/udhcp/common.c
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++++ busybox-1.29.3/networking/udhcp/common.c
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+@@ -270,6 +270,15 @@ uint8_t* FAST_FUNC udhcp_get_option(stru
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+ goto complain; /* complain and return NULL */
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+
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+ if (optionptr[OPT_CODE] == code) {
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++ if (optionptr[OPT_LEN] == 0) {
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++ /* So far no valid option with length 0 known.
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++ * Having this check means that searching
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++ * for DHCP_MESSAGE_TYPE need not worry
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++ * that returned pointer might be unsafe
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++ * to dereference.
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++ */
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++ goto complain; /* complain and return NULL */
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++ }
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+ log_option("option found", optionptr);
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+ return optionptr + OPT_DATA;
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+ }
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+@@ -287,6 +296,16 @@ uint8_t* FAST_FUNC udhcp_get_option(stru
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+ return NULL;
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+ }
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+
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++uint8_t* FAST_FUNC udhcp_get_option32(struct dhcp_packet *packet, int code)
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++{
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++ uint8_t *r = udhcp_get_option(packet, code);
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++ if (r) {
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++ if (r[-1] != 4)
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++ r = NULL;
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++ }
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++ return r;
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++}
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++
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+ /* Return the position of the 'end' option (no bounds checking) */
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+ int FAST_FUNC udhcp_end_option(uint8_t *optionptr)
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+ {
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+Index: busybox-1.29.3/networking/udhcp/common.h
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+===================================================================
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+--- busybox-1.29.3.orig/networking/udhcp/common.h
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++++ busybox-1.29.3/networking/udhcp/common.h
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+@@ -204,6 +204,10 @@ extern const uint8_t dhcp_option_lengths
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+ unsigned FAST_FUNC udhcp_option_idx(const char *name, const char *option_strings);
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+
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+ uint8_t *udhcp_get_option(struct dhcp_packet *packet, int code) FAST_FUNC;
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++/* Same as above + ensures that option length is 4 bytes
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++ * (returns NULL if size is different)
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++ */
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++uint8_t *udhcp_get_option32(struct dhcp_packet *packet, int code) FAST_FUNC;
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+ int udhcp_end_option(uint8_t *optionptr) FAST_FUNC;
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+ void udhcp_add_binary_option(struct dhcp_packet *packet, uint8_t *addopt) FAST_FUNC;
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+ #if ENABLE_UDHCPC || ENABLE_UDHCPD
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+Index: busybox-1.29.3/networking/udhcp/dhcpc.c
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+===================================================================
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+--- busybox-1.29.3.orig/networking/udhcp/dhcpc.c
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++++ busybox-1.29.3/networking/udhcp/dhcpc.c
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+@@ -1694,7 +1694,7 @@ int udhcpc_main(int argc UNUSED_PARAM, c
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+ * They say ISC DHCP client supports this case.
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+ */
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+ server_addr = 0;
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+- temp = udhcp_get_option(&packet, DHCP_SERVER_ID);
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++ temp = udhcp_get_option32(&packet, DHCP_SERVER_ID);
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+ if (!temp) {
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+ bb_error_msg("no server ID, using 0.0.0.0");
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+ } else {
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+@@ -1721,7 +1721,7 @@ int udhcpc_main(int argc UNUSED_PARAM, c
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+ struct in_addr temp_addr;
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+ uint8_t *temp;
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+
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+- temp = udhcp_get_option(&packet, DHCP_LEASE_TIME);
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++ temp = udhcp_get_option32(&packet, DHCP_LEASE_TIME);
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+ if (!temp) {
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+ bb_error_msg("no lease time with ACK, using 1 hour lease");
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+ lease_seconds = 60 * 60;
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+@@ -1817,7 +1817,7 @@ int udhcpc_main(int argc UNUSED_PARAM, c
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+ uint32_t svid;
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+ uint8_t *temp;
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+
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+- temp = udhcp_get_option(&packet, DHCP_SERVER_ID);
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++ temp = udhcp_get_option32(&packet, DHCP_SERVER_ID);
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+ if (!temp) {
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+ non_matching_svid:
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+ log1("received DHCP NAK with wrong"
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+Index: busybox-1.29.3/networking/udhcp/dhcpd.c
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+===================================================================
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+--- busybox-1.29.3.orig/networking/udhcp/dhcpd.c
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++++ busybox-1.29.3/networking/udhcp/dhcpd.c
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+@@ -640,7 +640,7 @@ static void add_server_options(struct dh
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+ static uint32_t select_lease_time(struct dhcp_packet *packet)
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+ {
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+ uint32_t lease_time_sec = server_config.max_lease_sec;
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+- uint8_t *lease_time_opt = udhcp_get_option(packet, DHCP_LEASE_TIME);
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++ uint8_t *lease_time_opt = udhcp_get_option32(packet, DHCP_LEASE_TIME);
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+ if (lease_time_opt) {
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+ move_from_unaligned32(lease_time_sec, lease_time_opt);
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+ lease_time_sec = ntohl(lease_time_sec);
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+@@ -987,7 +987,7 @@ int udhcpd_main(int argc UNUSED_PARAM, c
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+ }
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+
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+ /* Get SERVER_ID if present */
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+- server_id_opt = udhcp_get_option(&packet, DHCP_SERVER_ID);
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++ server_id_opt = udhcp_get_option32(&packet, DHCP_SERVER_ID);
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+ if (server_id_opt) {
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+ uint32_t server_id_network_order;
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+ move_from_unaligned32(server_id_network_order, server_id_opt);
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+@@ -1011,7 +1011,7 @@ int udhcpd_main(int argc UNUSED_PARAM, c
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+ }
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+
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+ /* Get REQUESTED_IP if present */
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+- requested_ip_opt = udhcp_get_option(&packet, DHCP_REQUESTED_IP);
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++ requested_ip_opt = udhcp_get_option32(&packet, DHCP_REQUESTED_IP);
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+ if (requested_ip_opt) {
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+ move_from_unaligned32(requested_nip, requested_ip_opt);
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+ }
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Armin Kuster