diff options
Diffstat (limited to 'dns.c')
| -rw-r--r-- | dns.c | 269 |
1 files changed, 269 insertions, 0 deletions
@@ -0,0 +1,269 @@ +#include <stdlib.h> +#include <string.h> +#include <stdio.h> + +#include "dns.h" + +flxDnsPacket* flx_dns_packet_new(void) { + flxDnsPacket *p; + p = g_new(flxDnsPacket, 1); + p->size = p->rindex = 2*6; + memset(p->data, 0, p->size); + return p; +} + +void flx_dns_packet_free(flxDnsPacket *p) { + g_assert(p); + g_free(p); +} + +void flx_dns_packet_set_field(flxDnsPacket *p, guint index, guint16 v) { + g_assert(p); + g_assert(index < 2*6); + + ((guint16*) p->data)[index] = g_htons(v); +} + +guint16 flx_dns_packet_get_field(flxDnsPacket *p, guint index) { + g_assert(p); + g_assert(index < 2*6); + + return g_ntohs(((guint16*) p->data)[index]); +} + +guint8* flx_dns_packet_append_name(flxDnsPacket *p, const gchar *name) { + guint8 *d, *f = NULL; + + g_assert(p); + g_assert(name); + + for (;;) { + guint n = strcspn(name, "."); + if (!n || n > 63) + return NULL; + + d = flx_dns_packet_extend(p, n+1); + if (!f) + f = d; + d[0] = n; + memcpy(d+1, name, n); + + name += n; + + /* no trailing dot */ + if (!*name) + break; + + name ++; + + /* trailing dot */ + if (!*name) + break; + } + + d = flx_dns_packet_extend(p, 1); + d[0] = 0; + + return f; +} + +guint8* flx_dns_packet_append_uint16(flxDnsPacket *p, guint16 v) { + guint8 *d; + + g_assert(p); + + d = flx_dns_packet_extend(p, sizeof(guint16)); + *((guint16*) d) = g_htons(v); + + return d; +} + +guint8 *flx_dns_packet_extend(flxDnsPacket *p, guint l) { + guint8 *d; + + g_assert(p); + g_assert(p->size+l <= sizeof(p->data)); + + d = p->data + p->size; + p->size += l; + + return d; +} + +guint8 *flx_dns_packet_append_name_compressed(flxDnsPacket *p, const gchar *name, guint8 *prev) { + guint16 *d; + signed long k; + g_assert(p); + + if (!prev) + return flx_dns_packet_append_name(p, name); + + k = prev - p->data; + if (k < 0 || k >= 0x4000 || (guint) k >= p->size) + return flx_dns_packet_append_name(p, name); + + d = (guint16*) flx_dns_packet_extend(p, sizeof(guint16)); + *d = g_htons((0xC000 | k)); + + return prev; +} + +gint flx_dns_packet_check_valid(flxDnsPacket *p) { + guint16 flags; + g_assert(p); + + if (p->size < 12) + return -1; + + flags = flx_dns_packet_get_field(p, DNS_FIELD_FLAGS); + + if (flags & DNS_FLAG_OPCODE || flags & DNS_FLAG_RCODE) + return -1; + + return 0; +} + +gint flx_dns_packet_check_valid_response(flxDnsPacket *p) { + guint16 flags; + g_assert(p); + + if (flx_dns_packet_check_valid(p) < 0) + return -1; + + flags = flx_dns_packet_get_field(p, DNS_FIELD_FLAGS); + + if (!(flags & DNS_FLAG_QR)) + return -1; + + if (flx_dns_packet_get_field(p, DNS_FIELD_QDCOUNT) > 0) + return -1; + + return 0; +} + +static gint consume_labels(flxDnsPacket *p, guint index, gchar *ret_name, guint l) { + gint ret = 0; + int compressed = 0; + int first_label = 1; + g_assert(p && ret_name && l); + + for (;;) { + guint8 n; + + if (index+1 > p->size) + return -1; + + n = p->data[index]; + + if (!n) { + index++; + if (!compressed) + ret++; + + if (l < 1) + return -1; + *ret_name = 0; + + return ret; + + } else if (n <= 63) { + /* Uncompressed label */ + index++; + if (!compressed) + ret++; + + if (index + n > p->size) + return -1; + + if ((guint) n + 1 > l) + return -1; + + if (!first_label) { + *(ret_name++) = '.'; + l--; + } else + first_label = 0; + + memcpy(ret_name, p->data + index, n); + index += n; + ret_name += n; + l -= n; + + if (!compressed) + ret += n; + } else if ((n & 0xC0) == 0xC0) { + /* Compressed label */ + + if (index+2 > p->size) + return -1; + + index = ((guint) (p->data[index] & ~0xC0)) << 8 | p->data[index+1]; + + if (!compressed) + ret += 2; + + compressed = 1; + } else + return -1; + } +} + +gint flx_dns_packet_consume_name(flxDnsPacket *p, gchar *ret_name, guint l) { + gint r; + + if ((r = consume_labels(p, p->rindex, ret_name, l)) < 0) + return -1; + + p->rindex += r; + return 0; +} + +gint flx_dns_packet_consume_uint16(flxDnsPacket *p, guint16 *ret_v) { + g_assert(p); + g_assert(ret_v); + + if (p->rindex + sizeof(guint16) > p->size) + return -1; + + *ret_v = g_ntohs(*((guint16*) (p->data + p->rindex))); + p->rindex += sizeof(guint16); + + return 0; +} + +gint flx_dns_packet_consume_uint32(flxDnsPacket *p, guint32 *ret_v) { + g_assert(p); + g_assert(ret_v); + + if (p->rindex + sizeof(guint32) > p->size) + return -1; + + *ret_v = g_ntohl(*((guint32*) (p->data + p->rindex))); + p->rindex += sizeof(guint32); + + return 0; +} + +gint flx_dns_packet_consume_bytes(flxDnsPacket *p, gpointer ret_data, guint l) { + g_assert(p); + g_assert(ret_data); + g_assert(l > 0); + + if (p->rindex + l > p->size) + return -1; + + memcpy(ret_data, p->data + p->rindex, l); + p->rindex += l; + + return 0; +} + +gint flx_dns_packet_skip(flxDnsPacket *p, guint length) { + g_assert(p); + + if (p->rindex + length > p->size) + return -1; + + p->rindex += length; + return 0; +} |