diff options
| -rw-r--r-- | lib/names-net.c | 153 |
1 files changed, 141 insertions, 12 deletions
diff --git a/lib/names-net.c b/lib/names-net.c index d96cc4d..9de73a7 100644 --- a/lib/names-net.c +++ b/lib/names-net.c @@ -18,6 +18,133 @@ #include <arpa/nameser.h> #include <resolv.h> +/* + * Unfortunately, there are no portable functions for DNS RR parsing, + * so we will do the bit shuffling with our own bare hands. + */ + +#define GET16(x) do { if (p+2 > end) goto err; x = (p[0] << 8) | p[1]; p += 2; } while (0) +#define GET32(x) do { if (p+4 > end) goto err; x = (p[0] << 24) | (p[1] << 16) | (p[2] << 8) | p[3]; p += 4; } while (0) + +enum dns_section { + DNS_SEC_QUESTION, + DNS_SEC_ANSWER, + DNS_SEC_AUTHORITY, + DNS_SEC_ADDITIONAL, + DNS_NUM_SECTIONS +}; + +struct dns_state { + u16 counts[DNS_NUM_SECTIONS]; + u8 *sections[DNS_NUM_SECTIONS+1]; + u8 *sec_ptr, *sec_end; + + /* Result of dns_parse_rr(): */ + u16 rr_type; + u16 rr_class; + u32 rr_ttl; + u16 rr_len; + u8 *rr_data; +}; + +static u8 * +dns_skip_name(u8 *p, u8 *end) +{ + while (p < end) + { + unsigned int x = *p++; + if (!x) + return p; + switch (x & 0xc0) + { + case 0: /* Uncompressed: x = length */ + p += x; + break; + case 0xc0: /* Indirection: 1 byte more for offset */ + p++; + return (p < end) ? p : NULL; + default: /* RFU */ + return NULL; + } + } + return NULL; +} + +static int +dns_parse_packet(struct dns_state *s, u8 *p, unsigned int plen) +{ + u8 *end = p + plen; + unsigned int i, j, x, len; + +#if 0 + /* Dump the packet */ + for (i=0; i<plen; i++) + { + if (!(i%16)) printf("%04x:", i); + printf(" %02x", p[i]); + if ((i%16)==15 || i==plen-1) putchar('\n'); + } +#endif + + GET32(x); /* ID and flags are ignored */ + for (i=0; i<DNS_NUM_SECTIONS; i++) + GET16(s->counts[i]); + for (i=0; i<DNS_NUM_SECTIONS; i++) + { + s->sections[i] = p; + for (j=0; j < s->counts[i]; j++) + { + p = dns_skip_name(p, end); /* Name */ + if (!p) + goto err; + GET32(x); /* Type and class */ + if (i != DNS_SEC_QUESTION) + { + GET32(x); /* TTL */ + GET16(len); /* Length of data */ + p += len; + if (p > end) + goto err; + } + } + } + s->sections[i] = p; + return 0; + +err: + return -1; +} + +static void +dns_init_section(struct dns_state *s, int i) +{ + s->sec_ptr = s->sections[i]; + s->sec_end = s->sections[i+1]; +} + +static int +dns_parse_rr(struct dns_state *s) +{ + byte *p = s->sec_ptr; + byte *end = s->sec_end; + + if (p == end) + return 0; + p = dns_skip_name(p, end); + if (!p) + goto err; + GET16(s->rr_type); + GET16(s->rr_class); + GET32(s->rr_ttl); + GET16(s->rr_len); + s->rr_data = p; + s->sec_ptr = p + s->rr_len; + return 1; + +err: + return -1; +} + char *pci_id_net_lookup(struct pci_access *a, int cat, int id1, int id2, int id3, int id4) { @@ -25,9 +152,8 @@ char char name[256], dnsname[256], txt[256], *domain; byte answer[4096]; const byte *data; - int res, i, j, dlen; - ns_msg m; - ns_rr rr; + int res, j, dlen; + struct dns_state ds; domain = pci_get_param(a, "net.domain"); if (!domain || !domain[0]) @@ -73,25 +199,28 @@ char a->debug("\tfailed, h_errno=%d\n", _res.res_h_errno); return NULL; } - if (ns_initparse(answer, res, &m) < 0) + if (dns_parse_packet(&ds, answer, res) < 0) { - a->debug("\tinitparse failed\n"); + a->debug("\tMalformed DNS packet received\n"); return NULL; } - for (i=0; ns_parserr(&m, ns_s_an, i, &rr) >= 0; i++) + dns_init_section(&ds, DNS_SEC_ANSWER); + while (dns_parse_rr(&ds) > 0) { - a->debug("\tanswer %d (class %d, type %d)\n", i, ns_rr_class(rr), ns_rr_type(rr)); - if (ns_rr_class(rr) != ns_c_in || ns_rr_type(rr) != ns_t_txt) - continue; - data = ns_rr_rdata(rr); - dlen = ns_rr_rdlen(rr); + if (ds.rr_class != ns_c_in || ds.rr_type != ns_t_txt) + { + a->debug("\tUnexpected RR in answer: class %d, type %d\n", ds.rr_class, ds.rr_type); + continue; + } + data = ds.rr_data; + dlen = ds.rr_len; j = 0; while (j < dlen && j+1+data[j] <= dlen) { memcpy(txt, &data[j+1], data[j]); txt[data[j]] = 0; j += 1+data[j]; - a->debug("\t\t%s\n", txt); + a->debug("\t\"%s\"\n", txt); if (txt[0] == 'i' && txt[1] == '=') return strdup(txt+2); } |