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dhcpc: cope with buggy DHCP servers which send oversized packets

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(Cristian Ionescu-Idbohrn <cristian.ionescu-idbohrn@axis.com>)
This commit is contained in:
Denis Vlasenko
2007-11-25 03:15:24 +00:00
parent a8875efa85
commit 72e76044cf
3 changed files with 27 additions and 3 deletions
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22
networking/udhcp/Config.in
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@@ -82,3 +82,25 @@ config FEATURE_RFC3397
help help
If selected, both client and server will support passing of domain If selected, both client and server will support passing of domain
search lists via option 119, specified in RFC3397. search lists via option 119, specified in RFC3397.
config UDHCPC_SLACK_FOR_BUGGY_SERVERS
int "DHCP options slack buffer size"
default 80
range 0 924
depends on APP_UDHCPD || APP_UDHCPC
help
Some buggy DHCP servers will send DHCP offer packets with option
field larger than we expect (which might also be considered a
buffer overflow attempt). These packets are normally discarded.
If circumstances beyond your control force you to support such
servers, this may help. The upper limit (924) makes dhcpc accept
even 1500 byte packets (maximum-sized ethernet packets).
This options does not make dhcp[cd] emit non-standard
sized packets.
Known buggy DHCP servers:
3Com OfficeConnect Remote 812 ADSL Router:
seems to confuse maximum allowed UDP packet size with
maximum size of entire IP packet, and sends packets which are
28 bytes too large.

6
networking/udhcp/common.h
View File

@@ -21,6 +21,8 @@ extern const uint8_t MAC_BCAST_ADDR[6]; /* six all-ones */
#include <netinet/udp.h> #include <netinet/udp.h>
#include <netinet/ip.h> #include <netinet/ip.h>
#define DHCP_OPTIONS_BUFSIZE 308
struct dhcpMessage { struct dhcpMessage {
uint8_t op; uint8_t op;
uint8_t htype; uint8_t htype;
@@ -37,7 +39,7 @@ struct dhcpMessage {
uint8_t sname[64]; uint8_t sname[64];
uint8_t file[128]; uint8_t file[128];
uint32_t cookie; uint32_t cookie;
uint8_t options[308]; /* 312 - cookie */ uint8_t options[DHCP_OPTIONS_BUFSIZE + CONFIG_UDHCPC_SLACK_FOR_BUGGY_SERVERS];
} ATTRIBUTE_PACKED; } ATTRIBUTE_PACKED;
struct udp_dhcp_packet { struct udp_dhcp_packet {
@@ -49,7 +51,7 @@ struct udp_dhcp_packet {
/* Let's see whether compiler understood us right */ /* Let's see whether compiler understood us right */
struct BUG_bad_sizeof_struct_udp_dhcp_packet { struct BUG_bad_sizeof_struct_udp_dhcp_packet {
char BUG_bad_sizeof_struct_udp_dhcp_packet char BUG_bad_sizeof_struct_udp_dhcp_packet
[sizeof(struct udp_dhcp_packet) != 576 ? -1 : 1]; [(sizeof(struct udp_dhcp_packet) != 576 + CONFIG_UDHCPC_SLACK_FOR_BUGGY_SERVERS) ? -1 : 1];
}; };
void udhcp_init_header(struct dhcpMessage *packet, char type); void udhcp_init_header(struct dhcpMessage *packet, char type);

2
networking/udhcp/options.c
View File

@@ -145,7 +145,7 @@ int add_option_string(uint8_t *optionptr, uint8_t *string)
int end = end_option(optionptr); int end = end_option(optionptr);
/* end position + string length + option code/length + end option */ /* end position + string length + option code/length + end option */
if (end + string[OPT_LEN] + 2 + 1 >= 308) { if (end + string[OPT_LEN] + 2 + 1 >= DHCP_OPTIONS_BUFSIZE) {
bb_error_msg("option 0x%02x did not fit into the packet", bb_error_msg("option 0x%02x did not fit into the packet",
string[OPT_CODE]); string[OPT_CODE]);
return 0; return 0;