diff options
Diffstat (limited to 'support/support_format_dns_packet.c')
| -rw-r--r-- | support/support_format_dns_packet.c | 222 |
1 files changed, 222 insertions, 0 deletions
diff --git a/support/support_format_dns_packet.c b/support/support_format_dns_packet.c new file mode 100644 index 0000000000..2992c57971 --- /dev/null +++ b/support/support_format_dns_packet.c @@ -0,0 +1,222 @@ +/* Convert a DNS packet to a human-readable representation. + Copyright (C) 2016-2017 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + <http://www.gnu.org/licenses/>. */ + +#include <support/format_nss.h> + +#include <arpa/inet.h> +#include <resolv.h> +#include <support/check.h> +#include <support/support.h> +#include <support/xmemstream.h> + +struct in_buffer +{ + const unsigned char *data; + size_t size; +}; + +static inline bool +extract_8 (struct in_buffer *in, unsigned char *value) +{ + if (in->size == 0) + return false; + *value = in->data[0]; + ++in->data; + --in->size; + return true; +} + +static inline bool +extract_16 (struct in_buffer *in, unsigned short *value) +{ + if (in->size < 2) + return false; + *value = (in->data[0] << 8) | in->data[1]; + in->data += 2; + in->size -= 2; + return true; +} + +static inline bool +extract_32 (struct in_buffer *in, unsigned *value) +{ + if (in->size < 4) + return false; + unsigned a = in->data[0]; + unsigned b = in->data[1]; + unsigned c = in->data[2]; + unsigned d = in->data[3]; + *value = (a << 24) | (b << 16) | (c << 8) | d; + in->data += 4; + in->size -= 4; + return true; +} + +static inline bool +extract_bytes (struct in_buffer *in, size_t length, struct in_buffer *value) +{ + if (in->size < length) + return false; + *value = (struct in_buffer) {in->data, length}; + in->data += length; + in->size -= length; + return true; +} + +struct dname +{ + char name[MAXDNAME + 1]; +}; + +static bool +extract_name (struct in_buffer full, struct in_buffer *in, struct dname *value) +{ + const unsigned char *full_end = full.data + full.size; + /* Sanity checks; these indicate buffer misuse. */ + TEST_VERIFY_EXIT + (!(in->data < full.data || in->data > full_end + || in->size > (size_t) (full_end - in->data))); + int ret = dn_expand (full.data, full_end, in->data, + value->name, sizeof (value->name)); + if (ret < 0) + return false; + in->data += ret; + in->size -= ret; + return true; +} + +char * +support_format_dns_packet (const unsigned char *buffer, size_t length) +{ + struct in_buffer full = { buffer, length }; + struct in_buffer in = full; + struct xmemstream mem; + xopen_memstream (&mem); + + unsigned short txnid; + unsigned short flags; + unsigned short qdcount; + unsigned short ancount; + unsigned short nscount; + unsigned short adcount; + if (!(extract_16 (&in, &txnid) + && extract_16 (&in, &flags) + && extract_16 (&in, &qdcount) + && extract_16 (&in, &ancount) + && extract_16 (&in, &nscount) + && extract_16 (&in, &adcount))) + { + fprintf (mem.out, "error: could not parse DNS header\n"); + goto out; + } + if (qdcount != 1) + { + fprintf (mem.out, "error: question count is %d, not 1\n", qdcount); + goto out; + } + struct dname qname; + if (!extract_name (full, &in, &qname)) + { + fprintf (mem.out, "error: malformed QNAME\n"); + goto out; + } + unsigned short qtype; + unsigned short qclass; + if (!(extract_16 (&in, &qtype) + && extract_16 (&in, &qclass))) + { + fprintf (mem.out, "error: malformed question\n"); + goto out; + } + if (qtype != T_A && qtype != T_AAAA && qtype != T_PTR) + { + fprintf (mem.out, "error: unsupported QTYPE %d\n", qtype); + goto out; + } + + fprintf (mem.out, "name: %s\n", qname.name); + + for (int i = 0; i < ancount; ++i) + { + struct dname rname; + if (!extract_name (full, &in, &rname)) + { + fprintf (mem.out, "error: malformed record name\n"); + goto out; + } + unsigned short rtype; + unsigned short rclass; + unsigned ttl; + unsigned short rdlen; + struct in_buffer rdata; + if (!(extract_16 (&in, &rtype) + && extract_16 (&in, &rclass) + && extract_32 (&in, &ttl) + && extract_16 (&in, &rdlen) + && extract_bytes (&in, rdlen, &rdata))) + { + fprintf (mem.out, "error: malformed record header\n"); + goto out; + } + /* Skip non-matching record types. */ + if ((rtype != qtype && rtype != T_CNAME) || rclass != qclass) + continue; + switch (rtype) + { + case T_A: + if (rdlen == 4) + fprintf (mem.out, "address: %d.%d.%d.%d\n", + rdata.data[0], + rdata.data[1], + rdata.data[2], + rdata.data[3]); + else + fprintf (mem.out, "error: A record of size %d: %s\n", + rdlen, rname.name); + break; + case T_AAAA: + { + if (rdlen == 16) + { + char buf[100]; + if (inet_ntop (AF_INET6, rdata.data, buf, sizeof (buf)) == NULL) + fprintf (mem.out, "error: AAAA record decoding failed: %m\n"); + else + fprintf (mem.out, "address: %s\n", buf); + } + else + fprintf (mem.out, "error: AAAA record of size %d: %s\n", + rdlen, rname.name); + } + break; + case T_CNAME: + case T_PTR: + { + struct dname name; + if (extract_name (full, &rdata, &name)) + fprintf (mem.out, "name: %s\n", name.name); + else + fprintf (mem.out, "error: malformed CNAME/PTR record\n"); + } + } + } + + out: + xfclose_memstream (&mem); + return mem.buffer; +} |