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532 lines
19 KiB
532 lines
19 KiB
commit e7c03f47651bd451ebf2c3c65899491d0bf7167e |
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Author: Florian Weimer <fweimer@redhat.com> |
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Date: Tue Aug 30 10:02:49 2022 +0200 |
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resolv: Add DNS packet parsing helpers geared towards wire format |
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The public parser functions around the ns_rr record type produce |
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textual domain names, but usually, this is not what we need while |
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parsing DNS packets within glibc. This commit adds two new helper |
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functions, __ns_rr_cursor_init and __ns_rr_cursor_next, for writing |
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packet parsers, and struct ns_rr_cursor, struct ns_rr_wire as |
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supporting types. |
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In theory, it is possible to avoid copying the owner name |
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into the rname field in __ns_rr_cursor_next, but this would need |
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more functions that work on compressed names. |
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Eventually, __res_context_send could be enhanced to preserve the |
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result of the packet parsing that is necessary for matching the |
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incoming UDP packets, so that this works does not have to be done |
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twice. |
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Reviewed-by: Siddhesh Poyarekar <siddhesh@sourceware.org> |
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(cherry picked from commit 857c890d9b42c50c8a94b76d47d4a61ab6d2f49c) |
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diff --git a/include/arpa/nameser.h b/include/arpa/nameser.h |
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index 6e4808f00d60caf9..c27e7886b7891997 100644 |
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--- a/include/arpa/nameser.h |
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+++ b/include/arpa/nameser.h |
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@@ -103,5 +103,97 @@ libc_hidden_proto (__libc_ns_samename) |
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must point one past the last byte in the packet. */ |
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int __ns_name_length_uncompressed (const unsigned char *p, |
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const unsigned char *eom) attribute_hidden; |
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+ |
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+/* Iterator over the resource records in a DNS packet. */ |
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+struct ns_rr_cursor |
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+{ |
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+ /* These members are not changed after initialization. */ |
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+ const unsigned char *begin; /* First byte of packet. */ |
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+ const unsigned char *end; /* One past the last byte of the packet. */ |
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+ const unsigned char *first_rr; /* First resource record (or packet end). */ |
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+ |
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+ /* Advanced towards the end while reading the packet. */ |
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+ const unsigned char *current; |
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+}; |
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+ |
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+/* Returns the RCODE field from the DNS header. */ |
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+static inline int |
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+ns_rr_cursor_rcode (const struct ns_rr_cursor *c) |
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+{ |
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+ return c->begin[3] & 0x0f; /* Lower 4 bits at offset 3. */ |
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+} |
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+ |
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+/* Returns the length of the answer section according to the DNS header. */ |
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+static inline int |
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+ns_rr_cursor_ancount (const struct ns_rr_cursor *c) |
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+{ |
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+ return c->begin[6] * 256 + c->begin[7]; /* 16 bits at offset 6. */ |
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+} |
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+ |
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+/* Returns the length of the authority (name server) section according |
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+ to the DNS header. */ |
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+static inline int |
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+ns_rr_cursor_nscount (const struct ns_rr_cursor *c) |
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+{ |
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+ return c->begin[8] * 256 + c->begin[9]; /* 16 bits at offset 8. */ |
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+} |
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+ |
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+/* Returns the length of the additional data section according to the |
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+ DNS header. */ |
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+static inline int |
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+ns_rr_cursor_adcount (const struct ns_rr_cursor *c) |
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+{ |
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+ return c->begin[10] * 256 + c->begin[11]; /* 16 bits at offset 10. */ |
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+} |
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+ |
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+/* Returns a pointer to the uncompressed question name in wire |
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+ format. */ |
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+static inline const unsigned char * |
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+ns_rr_cursor_qname (const struct ns_rr_cursor *c) |
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+{ |
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+ return c->begin + 12; /* QNAME starts right after the header. */ |
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+} |
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+ |
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+/* Returns the question type of the first and only question. */ |
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+static inline const int |
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+ns_rr_cursor_qtype (const struct ns_rr_cursor *c) |
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+{ |
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+ /* 16 bits 4 bytes back from the first RR header start. */ |
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+ return c->first_rr[-4] * 256 + c->first_rr[-3]; |
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+} |
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+ |
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+/* Returns the clss of the first and only question (usally C_IN). */ |
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+static inline const int |
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+ns_rr_cursor_qclass (const struct ns_rr_cursor *c) |
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+{ |
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+ /* 16 bits 2 bytes back from the first RR header start. */ |
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+ return c->first_rr[-2] * 256 + c->first_rr[-1]; |
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+} |
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+ |
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+/* Initializes *C to cover the packet [BUF, BUF+LEN). Returns false |
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+ if LEN is less than sizeof (*HD), if the packet does not contain a |
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+ full (uncompressed) question, or if the question count is not 1. */ |
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+_Bool __ns_rr_cursor_init (struct ns_rr_cursor *c, |
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+ const unsigned char *buf, size_t len) |
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+ attribute_hidden; |
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+ |
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+/* Like ns_rr, but the record owner name is not decoded into text format. */ |
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+struct ns_rr_wire |
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+{ |
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+ unsigned char rname[NS_MAXCDNAME]; /* Owner name of the record. */ |
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+ uint16_t rtype; /* Resource record type (T_*). */ |
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+ uint16_t rclass; /* Resource record class (C_*). */ |
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+ uint32_t ttl; /* Time-to-live field. */ |
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+ const unsigned char *rdata; /* Start of resource record data. */ |
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+ uint16_t rdlength; /* Length of the data at rdata, in bytes. */ |
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+}; |
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+ |
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+/* Attempts to parse the record at C into *RR. On success, return |
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+ true, and C is advanced past the record, and RR->rdata points to |
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+ the record data. On failure, errno is set to EMSGSIZE, and false |
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+ is returned. */ |
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+_Bool __ns_rr_cursor_next (struct ns_rr_cursor *c, struct ns_rr_wire *rr) |
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+ attribute_hidden; |
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+ |
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# endif /* !_ISOMAC */ |
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#endif |
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diff --git a/resolv/Makefile b/resolv/Makefile |
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index 308f18622a04965a..fded244d61068060 100644 |
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--- a/resolv/Makefile |
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+++ b/resolv/Makefile |
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@@ -47,6 +47,8 @@ routines := \ |
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ns_name_skip \ |
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ns_name_uncompress \ |
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ns_name_unpack \ |
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+ ns_rr_cursor_init \ |
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+ ns_rr_cursor_next \ |
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ns_samebinaryname \ |
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ns_samename \ |
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nsap_addr \ |
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@@ -117,6 +119,10 @@ tests-static += tst-ns_samebinaryname |
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tests-internal += tst-ns_name_length_uncompressed |
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tests-static += tst-ns_name_length_uncompressed |
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|
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+# Likewise for struct ns_rr_cursor and its functions. |
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+tests-internal += tst-ns_rr_cursor |
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+tests-static += tst-ns_rr_cursor |
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+ |
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# These tests need libdl. |
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ifeq (yes,$(build-shared)) |
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tests += \ |
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diff --git a/resolv/ns_rr_cursor_init.c b/resolv/ns_rr_cursor_init.c |
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new file mode 100644 |
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index 0000000000000000..6ee80b30e927ecb7 |
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--- /dev/null |
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+++ b/resolv/ns_rr_cursor_init.c |
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@@ -0,0 +1,62 @@ |
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+/* 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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+ |
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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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+ |
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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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+ |
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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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+ |
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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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+ |
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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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+ |
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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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+ |
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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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+ |
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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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+ |
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+ return true; |
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+} |
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diff --git a/resolv/ns_rr_cursor_next.c b/resolv/ns_rr_cursor_next.c |
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new file mode 100644 |
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index 0000000000000000..33652fc5da322d69 |
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--- /dev/null |
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+++ b/resolv/ns_rr_cursor_next.c |
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@@ -0,0 +1,74 @@ |
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+/* Simple DNS record parser without textual name decoding. |
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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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+ |
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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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+ |
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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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+ |
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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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+ |
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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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+ |
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+bool |
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+__ns_rr_cursor_next (struct ns_rr_cursor *c, struct ns_rr_wire *rr) |
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+{ |
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+ rr->rdata = NULL; |
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+ |
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+ /* Extract the record owner name. */ |
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+ int consumed = __ns_name_unpack (c->begin, c->end, c->current, |
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+ rr->rname, sizeof (rr->rname)); |
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+ if (consumed < 0) |
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+ { |
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+ memset (rr, 0, sizeof (*rr)); |
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+ __set_errno (EMSGSIZE); |
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+ return false; |
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+ } |
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+ c->current += consumed; |
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+ |
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+ /* Extract the metadata. */ |
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+ struct |
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+ { |
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+ uint16_t rtype; |
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+ uint16_t rclass; |
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+ uint32_t ttl; |
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+ uint16_t rdlength; |
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+ } __attribute__ ((packed)) metadata; |
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+ _Static_assert (sizeof (metadata) == 10, "sizeof metadata"); |
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+ if (c->end - c->current < sizeof (metadata)) |
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+ { |
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+ memset (rr, 0, sizeof (*rr)); |
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+ __set_errno (EMSGSIZE); |
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+ return false; |
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+ } |
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+ memcpy (&metadata, c->current, sizeof (metadata)); |
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+ c->current += sizeof (metadata); |
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+ /* Endianess conversion. */ |
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+ rr->rtype = ntohs (metadata.rtype); |
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+ rr->rclass = ntohs (metadata.rclass); |
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+ rr->ttl = ntohl (metadata.ttl); |
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+ rr->rdlength = ntohs (metadata.rdlength); |
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+ |
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+ /* Extract record data. */ |
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+ if (c->end - c->current < rr->rdlength) |
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+ { |
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+ memset (rr, 0, sizeof (*rr)); |
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+ __set_errno (EMSGSIZE); |
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+ return false; |
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+ } |
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+ rr->rdata = c->current; |
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+ c->current += rr->rdlength; |
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+ |
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+ return true; |
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+} |
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diff --git a/resolv/tst-ns_rr_cursor.c b/resolv/tst-ns_rr_cursor.c |
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new file mode 100644 |
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index 0000000000000000..c3c09089053d0c40 |
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--- /dev/null |
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+++ b/resolv/tst-ns_rr_cursor.c |
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@@ -0,0 +1,227 @@ |
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+/* Tests for resource record parsing. |
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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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+ |
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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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+ |
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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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+ |
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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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+ |
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+#include <arpa/nameser.h> |
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+#include <string.h> |
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+#include <support/check.h> |
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+#include <support/next_to_fault.h> |
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+ |
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+/* Reference packet for packet parsing. */ |
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+static const unsigned char valid_packet[] = |
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+ { 0x11, 0x12, 0x13, 0x14, |
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+ 0x00, 0x01, /* Question count. */ |
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+ 0x00, 0x02, /* Answer count. */ |
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+ 0x21, 0x22, 0x23, 0x24, /* Other counts (not actually in packet). */ |
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+ 3, 'w', 'w', 'w', 7, 'e', 'x', 'a', 'm', 'p', 'l', 'e', 0, |
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+ 0x00, 0x1c, /* Question type: AAAA. */ |
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+ 0x00, 0x01, /* Question class: IN. */ |
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+ 0xc0, 0x0c, /* Compression reference to QNAME. */ |
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+ 0x00, 0x1c, /* Record type: AAAA. */ |
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+ 0x00, 0x01, /* Record class: IN. */ |
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+ 0x12, 0x34, 0x56, 0x78, /* Record TTL. */ |
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+ 0x00, 0x10, /* Record data length (16 bytes). */ |
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+ 0x90, 0x91, 0x92, 0x93, 0x94, 0x95, 0x96, 0x97, |
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+ 0x98, 0x99, 0x9a, 0x9b, 0x9c, 0x9d, 0x9e, 0x9f, /* IPv6 address. */ |
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+ 0xc0, 0x0c, /* Compression reference to QNAME. */ |
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+ 0x00, 0x1c, /* Record type: AAAA. */ |
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+ 0x00, 0x01, /* Record class: IN. */ |
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+ 0x11, 0x33, 0x55, 0x77, /* Record TTL. */ |
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+ 0x00, 0x10, /* Record data length (16 bytes). */ |
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+ 0xa0, 0xa1, 0xa2, 0xa3, 0xa4, 0xa5, 0xa6, 0xa7, |
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+ 0xa8, 0xa9, 0xaa, 0xab, 0xac, 0xad, 0xae, 0xaf, /* IPv6 address. */ |
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+ }; |
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+ |
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+/* Special offsets in valid_packet. */ |
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+enum |
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+ { |
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+ offset_of_first_record = 29, |
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+ offset_of_second_record = 57, |
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+ }; |
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+ |
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+/* Check that parsing valid_packet succeeds. */ |
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+static void |
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+test_valid (void) |
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+{ |
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+ struct ns_rr_cursor c; |
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+ TEST_VERIFY_EXIT (__ns_rr_cursor_init (&c, valid_packet, |
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+ sizeof (valid_packet))); |
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+ TEST_COMPARE (ns_rr_cursor_rcode (&c), 4); |
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+ TEST_COMPARE (ns_rr_cursor_ancount (&c), 2); |
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+ TEST_COMPARE (ns_rr_cursor_nscount (&c), 0x2122); |
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+ TEST_COMPARE (ns_rr_cursor_adcount (&c), 0x2324); |
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+ TEST_COMPARE_BLOB (ns_rr_cursor_qname (&c), 13, &valid_packet[12], 13); |
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+ TEST_COMPARE (ns_rr_cursor_qtype (&c), T_AAAA); |
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+ TEST_COMPARE (ns_rr_cursor_qclass (&c), C_IN); |
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+ TEST_COMPARE (c.current - valid_packet, offset_of_first_record); |
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+ |
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+ struct ns_rr_wire r; |
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+ TEST_VERIFY_EXIT (__ns_rr_cursor_next (&c, &r)); |
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+ TEST_COMPARE (r.rtype, T_AAAA); |
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+ TEST_COMPARE (r.rclass, C_IN); |
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+ TEST_COMPARE (r.ttl, 0x12345678); |
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+ TEST_COMPARE_BLOB (r.rdata, r.rdlength, |
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+ "\x90\x91\x92\x93\x94\x95\x96\x97" |
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+ "\x98\x99\x9a\x9b\x9c\x9d\x9e\x9f", 16); |
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+ TEST_COMPARE (c.current - valid_packet, offset_of_second_record); |
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+ TEST_VERIFY_EXIT (__ns_rr_cursor_next (&c, &r)); |
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+ TEST_COMPARE (r.rtype, T_AAAA); |
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+ TEST_COMPARE (r.rclass, C_IN); |
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+ TEST_COMPARE (r.ttl, 0x11335577); |
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+ TEST_COMPARE_BLOB (r.rdata, r.rdlength, |
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+ "\xa0\xa1\xa2\xa3\xa4\xa5\xa6\xa7" |
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+ "\xa8\xa9\xaa\xab\xac\xad\xae\xaf", 16); |
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+ TEST_VERIFY (c.current == c.end); |
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+} |
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+ |
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+/* Check that trying to parse a packet with a compressed QNAME fails. */ |
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+static void |
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+test_compressed_qname (void) |
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+{ |
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+ static const unsigned char packet[] = |
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+ { 0x11, 0x12, 0x13, 0x14, |
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+ 0x00, 0x01, /* Question count. */ |
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+ 0x00, 0x00, /* Answer count. */ |
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+ 0x00, 0x00, 0x00, 0x00, /* Other counts. */ |
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+ 3, 'w', 'w', 'w', 7, 'e', 'x', 'a', 'm', 'p', 'l', 'e', 0xc0, 0x04, |
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+ 0x00, 0x01, /* Question type: A. */ |
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+ 0x00, 0x01, /* Question class: IN. */ |
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+ }; |
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+ |
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+ struct ns_rr_cursor c; |
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+ TEST_VERIFY_EXIT (!__ns_rr_cursor_init (&c, packet, sizeof (packet))); |
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+} |
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+ |
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+/* Check that trying to parse a packet with two questions fails. */ |
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+static void |
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+test_two_questions (void) |
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+{ |
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+ static const unsigned char packet[] = |
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+ { 0x11, 0x12, 0x13, 0x14, |
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+ 0x00, 0x02, /* Question count. */ |
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+ 0x00, 0x00, /* Answer count. */ |
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+ 0x00, 0x00, 0x00, 0x00, /* Other counts. */ |
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+ 3, 'w', 'w', 'w', 7, 'e', 'x', 'a', 'm', 'p', 'l', 'e', 0xc0, 0x04, |
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+ 0x00, 0x01, /* Question type: A. */ |
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+ 0x00, 0x01, /* Question class: IN. */ |
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+ 3, 'w', 'w', 'w', 7, 'e', 'x', 'a', 'm', 'p', 'l', 'e', 0xc0, 0x04, |
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+ 0x00, 0x1c, /* Question type: AAAA. */ |
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+ 0x00, 0x01, /* Question class: IN. */ |
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+ }; |
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+ |
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+ struct ns_rr_cursor c; |
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+ TEST_VERIFY_EXIT (!__ns_rr_cursor_init (&c, packet, sizeof (packet))); |
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+} |
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+ |
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+/* Used to check that parsing truncated packets does not over-read. */ |
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+static struct support_next_to_fault ntf; |
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+ |
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+/* Truncated packet in the second resource record. */ |
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+static void |
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+test_truncated_one_rr (size_t length) |
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+{ |
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+ unsigned char *end = (unsigned char *) ntf.buffer - ntf.length; |
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+ unsigned char *start = end - length; |
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+ |
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+ /* Produce the truncated packet. */ |
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+ memcpy (start, valid_packet, length); |
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+ |
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+ struct ns_rr_cursor c; |
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+ TEST_VERIFY_EXIT (__ns_rr_cursor_init (&c, start, length)); |
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+ TEST_COMPARE (ns_rr_cursor_rcode (&c), 4); |
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+ TEST_COMPARE (ns_rr_cursor_ancount (&c), 2); |
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+ TEST_COMPARE (ns_rr_cursor_nscount (&c), 0x2122); |
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+ TEST_COMPARE (ns_rr_cursor_adcount (&c), 0x2324); |
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+ TEST_COMPARE_BLOB (ns_rr_cursor_qname (&c), 13, &valid_packet[12], 13); |
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+ TEST_COMPARE (ns_rr_cursor_qtype (&c), T_AAAA); |
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+ TEST_COMPARE (ns_rr_cursor_qclass (&c), C_IN); |
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+ TEST_COMPARE (c.current - start, offset_of_first_record); |
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+ |
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+ struct ns_rr_wire r; |
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+ TEST_VERIFY_EXIT (__ns_rr_cursor_next (&c, &r)); |
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+ TEST_COMPARE (r.rtype, T_AAAA); |
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+ TEST_COMPARE (r.rclass, C_IN); |
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+ TEST_COMPARE (r.ttl, 0x12345678); |
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+ TEST_COMPARE_BLOB (r.rdata, r.rdlength, |
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+ "\x90\x91\x92\x93\x94\x95\x96\x97" |
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+ "\x98\x99\x9a\x9b\x9c\x9d\x9e\x9f", 16); |
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+ TEST_COMPARE (c.current - start, offset_of_second_record); |
|
+ TEST_VERIFY (!__ns_rr_cursor_next (&c, &r)); |
|
+} |
|
+ |
|
+/* Truncated packet in the first resource record. */ |
|
+static void |
|
+test_truncated_no_rr (size_t length) |
|
+{ |
|
+ unsigned char *end = (unsigned char *) ntf.buffer - ntf.length; |
|
+ unsigned char *start = end - length; |
|
+ |
|
+ /* Produce the truncated packet. */ |
|
+ memcpy (start, valid_packet, length); |
|
+ |
|
+ struct ns_rr_cursor c; |
|
+ TEST_VERIFY_EXIT (__ns_rr_cursor_init (&c, start, length)); |
|
+ TEST_COMPARE (ns_rr_cursor_rcode (&c), 4); |
|
+ TEST_COMPARE (ns_rr_cursor_ancount (&c), 2); |
|
+ TEST_COMPARE (ns_rr_cursor_nscount (&c), 0x2122); |
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+ TEST_COMPARE (ns_rr_cursor_adcount (&c), 0x2324); |
|
+ TEST_COMPARE_BLOB (ns_rr_cursor_qname (&c), 13, &valid_packet[12], 13); |
|
+ TEST_COMPARE (ns_rr_cursor_qtype (&c), T_AAAA); |
|
+ TEST_COMPARE (ns_rr_cursor_qclass (&c), C_IN); |
|
+ TEST_COMPARE (c.current - start, offset_of_first_record); |
|
+ |
|
+ struct ns_rr_wire r; |
|
+ TEST_VERIFY (!__ns_rr_cursor_next (&c, &r)); |
|
+} |
|
+ |
|
+/* Truncated packet before first resource record. */ |
|
+static void |
|
+test_truncated_before_rr (size_t length) |
|
+{ |
|
+ unsigned char *end = (unsigned char *) ntf.buffer - ntf.length; |
|
+ unsigned char *start = end - length; |
|
+ |
|
+ /* Produce the truncated packet. */ |
|
+ memcpy (start, valid_packet, length); |
|
+ |
|
+ struct ns_rr_cursor c; |
|
+ TEST_VERIFY_EXIT (!__ns_rr_cursor_init (&c, start, length)); |
|
+} |
|
+ |
|
+static int |
|
+do_test (void) |
|
+{ |
|
+ ntf = support_next_to_fault_allocate (sizeof (valid_packet)); |
|
+ |
|
+ test_valid (); |
|
+ test_compressed_qname (); |
|
+ test_two_questions (); |
|
+ |
|
+ for (int length = offset_of_second_record; length < sizeof (valid_packet); |
|
+ ++length) |
|
+ test_truncated_one_rr (length); |
|
+ for (int length = offset_of_first_record; length < offset_of_second_record; |
|
+ ++length) |
|
+ test_truncated_no_rr (length); |
|
+ for (int length = 0; length < offset_of_first_record; ++length) |
|
+ test_truncated_before_rr (length); |
|
+ |
|
+ support_next_to_fault_free (&ntf); |
|
+ return 0; |
|
+} |
|
+ |
|
+#include <support/test-driver.c>
|
|
|