diff options
| -rw-r--r-- | networking/udhcp/Config.in | 22 | ||||
| -rw-r--r-- | networking/udhcp/common.h | 6 | ||||
| -rw-r--r-- | networking/udhcp/options.c | 2 |
3 files changed, 27 insertions, 3 deletions
diff --git a/networking/udhcp/Config.in b/networking/udhcp/Config.in index 734db65..1aef69b 100644 --- a/networking/udhcp/Config.in +++ b/networking/udhcp/Config.in @@ -82,3 +82,25 @@ config FEATURE_RFC3397 help If selected, both client and server will support passing of domain 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. diff --git a/networking/udhcp/common.h b/networking/udhcp/common.h index 4f2d31c..eecb72c 100644 --- a/networking/udhcp/common.h +++ b/networking/udhcp/common.h @@ -21,6 +21,8 @@ extern const uint8_t MAC_BCAST_ADDR[6]; /* six all-ones */ #include <netinet/udp.h> #include <netinet/ip.h> +#define DHCP_OPTIONS_BUFSIZE 308 + struct dhcpMessage { uint8_t op; uint8_t htype; @@ -37,7 +39,7 @@ struct dhcpMessage { uint8_t sname[64]; uint8_t file[128]; uint32_t cookie; - uint8_t options[308]; /* 312 - cookie */ + uint8_t options[DHCP_OPTIONS_BUFSIZE + CONFIG_UDHCPC_SLACK_FOR_BUGGY_SERVERS]; } ATTRIBUTE_PACKED; struct udp_dhcp_packet { @@ -49,7 +51,7 @@ struct udp_dhcp_packet { /* Let's see whether compiler understood us right */ struct 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); diff --git a/networking/udhcp/options.c b/networking/udhcp/options.c index 2b4f164..6744e2a 100644 --- a/networking/udhcp/options.c +++ b/networking/udhcp/options.c @@ -145,7 +145,7 @@ int add_option_string(uint8_t *optionptr, uint8_t *string) int end = end_option(optionptr); /* 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", string[OPT_CODE]); return 0; |