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857c890d9b
The public parser functions around the ns_rr record type produce textual domain names, but usually, this is not what we need while parsing DNS packets within glibc. This commit adds two new helper functions, __ns_rr_cursor_init and __ns_rr_cursor_next, for writing packet parsers, and struct ns_rr_cursor, struct ns_rr_wire as supporting types. In theory, it is possible to avoid copying the owner name into the rname field in __ns_rr_cursor_next, but this would need more functions that work on compressed names. Eventually, __res_context_send could be enhanced to preserve the result of the packet parsing that is necessary for matching the incoming UDP packets, so that this works does not have to be done twice. Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org>
63 lines
1.8 KiB
C
63 lines
1.8 KiB
C
/* Initialize a simple DNS packet parser.
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Copyright (C) 2022 Free Software Foundation, Inc.
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This file is part of the GNU C Library.
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The GNU C Library is free software; you can redistribute it and/or
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modify it under the terms of the GNU Lesser General Public
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License as published by the Free Software Foundation; either
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version 2.1 of the License, or (at your option) any later version.
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The GNU C Library is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public
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License along with the GNU C Library; if not, see
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<https://www.gnu.org/licenses/>. */
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#include <arpa/nameser.h>
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#include <errno.h>
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#include <stdbool.h>
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#include <string.h>
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bool
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__ns_rr_cursor_init (struct ns_rr_cursor *c,
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const unsigned char *buf, size_t len)
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{
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c->begin = buf;
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c->end = buf + len;
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/* Check for header size and 16-bit question count value (it must be 1). */
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if (len < 12 || buf[4] != 0 || buf[5] != 1)
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{
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__set_errno (EMSGSIZE);
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c->current = c->end;
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return false;
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}
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c->current = buf + 12;
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int consumed = __ns_name_length_uncompressed (c->current, c->end);
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if (consumed < 0)
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{
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__set_errno (EMSGSIZE);
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c->current = c->end;
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c->first_rr = NULL;
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return false;
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}
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c->current += consumed;
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/* Ensure there is room for question type and class. */
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if (c->end - c->current < 4)
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{
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__set_errno (EMSGSIZE);
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c->current = c->end;
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c->first_rr = NULL;
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return false;
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}
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c->current += 4;
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c->first_rr = c->current;
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return true;
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}
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