diff options
Diffstat (limited to 'resolv/res-noaaaa.c')
| -rw-r--r-- | resolv/res-noaaaa.c | 143 |
1 files changed, 143 insertions, 0 deletions
diff --git a/resolv/res-noaaaa.c b/resolv/res-noaaaa.c new file mode 100644 index 0000000000..4ba197664a --- /dev/null +++ b/resolv/res-noaaaa.c @@ -0,0 +1,143 @@ +/* Implement suppression of AAAA queries. + Copyright (C) 2022 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 + <https://www.gnu.org/licenses/>. */ + +#include <resolv.h> +#include <string.h> +#include <resolv-internal.h> +#include <resolv_context.h> +#include <arpa/nameser.h> + +/* Returns true if the question type at P matches EXPECTED, and the + class is IN. */ +static bool +qtype_matches (const unsigned char *p, int expected) +{ + /* This assumes that T_A/C_IN constants are less than 256, which + they are. */ + return p[0] == 0 && p[1] == expected && p[2] == 0 && p[3] == C_IN; +} + +/* Handle RES_NOAAAA translation of AAAA queries. To produce a Name + Error (NXDOMAIN) repsonse for domain names that do not exist, it is + still necessary to send a query. Using question type A is a + conservative choice. In the returned answer, it is necessary to + switch back the question type to AAAA. */ +bool +__res_handle_no_aaaa (struct resolv_context *ctx, + const unsigned char *buf, int buflen, + unsigned char *ans, int anssiz, int *result) +{ + /* AAAA mode is not active, or the query looks invalid (will not be + able to be parsed). */ + if ((ctx->resp->options & RES_NOAAAA) == 0 + || buflen <= sizeof (HEADER)) + return false; + + /* The replacement A query is produced here. */ + struct + { + HEADER header; + unsigned char question[NS_MAXCDNAME + 4]; + } replacement; + memcpy (&replacement.header, buf, sizeof (replacement.header)); + + if (replacement.header.qr + || replacement.header.opcode != 0 + || replacement.header.rcode != 0 + || ntohs (replacement.header.qdcount) != 1 + || ntohs (replacement.header.ancount) != 0 + || ntohs (replacement.header.nscount) != 0) + /* Not a well-formed question. Let the core resolver code produce + the proper error. */ + return false; + + /* Disable EDNS0. */ + replacement.header.arcount = htons (0); + + /* Extract the QNAME. */ + int ret = __ns_name_unpack (buf, buf + buflen, buf + sizeof (HEADER), + replacement.question, NS_MAXCDNAME); + if (ret < 0) + /* Format error. */ + return false; + + /* Compute the end of the question name. */ + const unsigned char *after_question = buf + sizeof (HEADER) + ret; + + /* Check that we are dealing with an AAAA query. */ + if (buf + buflen - after_question < 4 + || !qtype_matches (after_question, T_AAAA)) + return false; + + /* Find the place to store the type/class data in the replacement + query. */ + after_question = replacement.question; + /* This cannot fail because __ns_name_unpack above produced a valid + domain name. */ + (void) __ns_name_skip (&after_question, &replacement.question[NS_MAXCDNAME]); + unsigned char *start_of_query = (unsigned char *) &replacement; + const unsigned char *end_of_query = after_question + 4; + + /* Produce an A/IN query. */ + { + unsigned char *p = (unsigned char *) after_question; + p[0] = 0; + p[1] = T_A; + p[2] = 0; + p[3] = C_IN; + } + + /* Clear the output buffer, to avoid reading undefined data when + rewriting the result from A to AAAA. */ + memset (ans, 0, anssiz); + + /* Always perform the message translation, independent of the error + code. */ + ret = __res_context_send (ctx, + start_of_query, end_of_query - start_of_query, + NULL, 0, ans, anssiz, + NULL, NULL, NULL, NULL, NULL); + + /* Patch in the AAAA question type if there is room and the A query + type was received. */ + after_question = ans + sizeof (HEADER); + if (__ns_name_skip (&after_question, ans + anssiz) == 0 + && ans + anssiz - after_question >= 4 + && qtype_matches (after_question, T_A)) + { + ((unsigned char *) after_question)[1] = T_AAAA; + + /* Create an aligned copy of the header. Hide all data except + the question from the response. Put back the header. There is + no need to change the response code. The zero answer count turns + a positive response with data into a no-data response. */ + memcpy (&replacement.header, ans, sizeof (replacement.header)); + replacement.header.ancount = htons (0); + replacement.header.nscount = htons (0); + replacement.header.arcount = htons (0); + memcpy (ans, &replacement.header, sizeof (replacement.header)); + + /* Truncate the reply. */ + if (ret <= 0) + *result = ret; + else + *result = after_question - ans + 4; + } + + return true; +} |