1 /* -*- Mode: C; tab-width: 4 -*-
2  *
3  * Copyright (c) 2004-2018 Apple Inc. All rights reserved.
4  *
5  * Redistribution and use in source and binary forms, with or without
6  * modification, are permitted provided that the following conditions are met:
7  *
8  * 1.  Redistributions of source code must retain the above copyright notice,
9  *     this list of conditions and the following disclaimer.
10  * 2.  Redistributions in binary form must reproduce the above copyright notice,
11  *     this list of conditions and the following disclaimer in the documentation
12  *     and/or other materials provided with the distribution.
13  * 3.  Neither the name of Apple Inc. ("Apple") nor the names of its
14  *     contributors may be used to endorse or promote products derived from this
15  *     software without specific prior written permission.
16  *
17  * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
18  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
19  * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
20  * DISCLAIMED. IN NO EVENT SHALL APPLE OR ITS CONTRIBUTORS BE LIABLE FOR ANY
21  * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
22  * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
23  * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
24  * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
25  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
26  * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27  */
28 
29 #include <stdlib.h>
30 #include <string.h>
31 
32 #include "dns_sd.h"
33 
34 #if defined(_WIN32)
35 // disable warning "conversion from <data> to uint16_t"
36 #pragma warning(disable:4244)
37 #define strncasecmp _strnicmp
38 #define strcasecmp _stricmp
39 #endif
40 
41 /*********************************************************************************************
42 *
43 *  Supporting Functions
44 *
45 *********************************************************************************************/
46 
47 #define mDNSIsDigit(X)     ((X) >= '0' && (X) <= '9')
48 
49 // DomainEndsInDot returns 1 if name ends with a dot, 0 otherwise
50 // (DNSServiceConstructFullName depends this returning 1 for true, rather than any non-zero value meaning true)
51 
DomainEndsInDot(const char * dom)52 static int DomainEndsInDot(const char *dom)
53 {
54     while (dom[0] && dom[1])
55     {
56         if (dom[0] == '\\') // advance past escaped byte sequence
57         {
58             if (mDNSIsDigit(dom[1]) && mDNSIsDigit(dom[2]) && mDNSIsDigit(dom[3]))
59                 dom += 4;           // If "\ddd"    then skip four
60             else dom += 2;          // else if "\x" then skip two
61         }
62         else dom++;                 // else goto next character
63     }
64     return (dom[0] == '.');
65 }
66 
InternalTXTRecordSearch(uint16_t txtLen,const void * txtRecord,const char * key,unsigned long * keylen)67 static uint8_t *InternalTXTRecordSearch
68 (
69     uint16_t txtLen,
70     const void       *txtRecord,
71     const char       *key,
72     unsigned long    *keylen
73 )
74 {
75     uint8_t *p = (uint8_t*)txtRecord;
76     uint8_t *e = p + txtLen;
77     *keylen = (unsigned long) strlen(key);
78     while (p<e)
79     {
80         uint8_t *x = p;
81         p += 1 + p[0];
82         if (p <= e && *keylen <= x[0] && !strncasecmp(key, (char*)x+1, *keylen))
83             if (*keylen == x[0] || x[1+*keylen] == '=') return(x);
84     }
85     return(NULL);
86 }
87 
88 /*********************************************************************************************
89 *
90 *  General Utility Functions
91 *
92 *********************************************************************************************/
93 
94 // Note: Need to make sure we don't write more than kDNSServiceMaxDomainName (1009) bytes to fullName
95 // In earlier builds this constant was defined to be 1005, so to avoid buffer overruns on clients
96 // compiled with that constant we'll actually limit the output to 1005 bytes.
97 
DNSServiceConstructFullName(char * const fullName,const char * const service,const char * const regtype,const char * const domain)98 DNSServiceErrorType DNSSD_API DNSServiceConstructFullName
99 (
100     char       *const fullName,
101     const char *const service,      // May be NULL
102     const char *const regtype,
103     const char *const domain
104 )
105 {
106     const size_t len = !regtype ? 0 : strlen(regtype) - DomainEndsInDot(regtype);
107     char       *fn   = fullName;
108     char *const lim  = fullName + 1005;
109     const char *s    = service;
110     const char *r    = regtype;
111     const char *d    = domain;
112 
113     // regtype must be at least "x._udp" or "x._tcp"
114     if (len < 6 || !domain || !domain[0]) return kDNSServiceErr_BadParam;
115     if (strncasecmp((regtype + len - 4), "_tcp", 4) && strncasecmp((regtype + len - 4), "_udp", 4)) return kDNSServiceErr_BadParam;
116 
117     if (service && *service)
118     {
119         while (*s)
120         {
121             unsigned char c = *s++;             // Needs to be unsigned, or values like 0xFF will be interpreted as < 32
122             if (c <= ' ')                       // Escape non-printable characters
123             {
124                 if (fn+4 >= lim) goto fail;
125                 *fn++ = '\\';
126                 *fn++ = '0' + (c / 100);
127                 *fn++ = '0' + (c /  10) % 10;
128                 c     = '0' + (c      ) % 10;
129             }
130             else if (c == '.' || (c == '\\'))   // Escape dot and backslash literals
131             {
132                 if (fn+2 >= lim) goto fail;
133                 *fn++ = '\\';
134             }
135             else
136             if (fn+1 >= lim) goto fail;
137             *fn++ = (char)c;
138         }
139         *fn++ = '.';
140     }
141 
142     while (*r) if (fn+1 >= lim) goto fail;else *fn++ = *r++;
143     if (!DomainEndsInDot(regtype)) { if (fn+1 >= lim) goto fail;else *fn++ = '.';}
144 
145     while (*d) if (fn+1 >= lim) goto fail;else *fn++ = *d++;
146     if (!DomainEndsInDot(domain)) { if (fn+1 >= lim) goto fail;else *fn++ = '.';}
147 
148     *fn = '\0';
149     return kDNSServiceErr_NoError;
150 
151 fail:
152     *fn = '\0';
153     return kDNSServiceErr_BadParam;
154 }
155 
156 /*********************************************************************************************
157 *
158 *   TXT Record Construction Functions
159 *
160 *********************************************************************************************/
161 
162 typedef struct _TXTRecordRefRealType
163 {
164     uint8_t  *buffer;       // Pointer to data
165     uint16_t buflen;        // Length of buffer
166     uint16_t datalen;       // Length currently in use
167     uint16_t malloced;  // Non-zero if buffer was allocated via malloc()
168 } TXTRecordRefRealType;
169 
170 #define txtRec ((TXTRecordRefRealType*)txtRecord)
171 
172 // The opaque storage defined in the public dns_sd.h header is 16 bytes;
173 // make sure we don't exceed that.
174 struct CompileTimeAssertionCheck_dnssd_clientlib
175 {
176     char assert0[(sizeof(TXTRecordRefRealType) <= 16) ? 1 : -1];
177 };
178 
TXTRecordCreate(TXTRecordRef * txtRecord,uint16_t bufferLen,void * buffer)179 void DNSSD_API TXTRecordCreate
180 (
181     TXTRecordRef     *txtRecord,
182     uint16_t bufferLen,
183     void             *buffer
184 )
185 {
186     txtRec->buffer   = buffer;
187     txtRec->buflen   = buffer ? bufferLen : (uint16_t)0;
188     txtRec->datalen  = 0;
189     txtRec->malloced = 0;
190 }
191 
TXTRecordDeallocate(TXTRecordRef * txtRecord)192 void DNSSD_API TXTRecordDeallocate(TXTRecordRef *txtRecord)
193 {
194     if (txtRec->malloced) free(txtRec->buffer);
195 }
196 
TXTRecordSetValue(TXTRecordRef * txtRecord,const char * key,uint8_t valueSize,const void * value)197 DNSServiceErrorType DNSSD_API TXTRecordSetValue
198 (
199     TXTRecordRef     *txtRecord,
200     const char       *key,
201     uint8_t valueSize,
202     const void       *value
203 )
204 {
205     uint8_t *start, *p;
206     const char *k;
207     unsigned long keysize, keyvalsize;
208 
209     for (k = key; *k; k++) if (*k < 0x20 || *k > 0x7E || *k == '=') return(kDNSServiceErr_Invalid);
210     keysize = (unsigned long)(k - key);
211     keyvalsize = 1 + keysize + (value ? (1 + valueSize) : 0);
212     if (keysize < 1 || keyvalsize > 255) return(kDNSServiceErr_Invalid);
213     (void)TXTRecordRemoveValue(txtRecord, key);
214     if (txtRec->datalen + keyvalsize > txtRec->buflen)
215     {
216         unsigned char *newbuf;
217         unsigned long newlen = txtRec->datalen + keyvalsize;
218         if (newlen > 0xFFFF) return(kDNSServiceErr_Invalid);
219         newbuf = malloc((size_t)newlen);
220         if (!newbuf) return(kDNSServiceErr_NoMemory);
221         memcpy(newbuf, txtRec->buffer, txtRec->datalen);
222         if (txtRec->malloced) free(txtRec->buffer);
223         txtRec->buffer = newbuf;
224         txtRec->buflen = (uint16_t)(newlen);
225         txtRec->malloced = 1;
226     }
227     start = txtRec->buffer + txtRec->datalen;
228     p = start + 1;
229     memcpy(p, key, keysize);
230     p += keysize;
231     if (value)
232     {
233         *p++ = '=';
234         memcpy(p, value, valueSize);
235         p += valueSize;
236     }
237     *start = (uint8_t)(p - start - 1);
238     txtRec->datalen += p - start;
239     return(kDNSServiceErr_NoError);
240 }
241 
TXTRecordRemoveValue(TXTRecordRef * txtRecord,const char * key)242 DNSServiceErrorType DNSSD_API TXTRecordRemoveValue
243 (
244     TXTRecordRef     *txtRecord,
245     const char       *key
246 )
247 {
248     unsigned long keylen, itemlen, remainder;
249     uint8_t *item = InternalTXTRecordSearch(txtRec->datalen, txtRec->buffer, key, &keylen);
250     if (!item) return(kDNSServiceErr_NoSuchKey);
251     itemlen   = (unsigned long)(1 + item[0]);
252     remainder = (unsigned long)((txtRec->buffer + txtRec->datalen) - (item + itemlen));
253     // Use memmove because memcpy behaviour is undefined for overlapping regions
254     memmove(item, item + itemlen, remainder);
255     txtRec->datalen -= itemlen;
256     return(kDNSServiceErr_NoError);
257 }
258 
TXTRecordGetLength(const TXTRecordRef * txtRecord)259 uint16_t DNSSD_API TXTRecordGetLength  (const TXTRecordRef *txtRecord) { return(txtRec->datalen); }
TXTRecordGetBytesPtr(const TXTRecordRef * txtRecord)260 const void * DNSSD_API TXTRecordGetBytesPtr(const TXTRecordRef *txtRecord) { return(txtRec->buffer); }
261 
262 /*********************************************************************************************
263 *
264 *   TXT Record Parsing Functions
265 *
266 *********************************************************************************************/
267 
TXTRecordContainsKey(uint16_t txtLen,const void * txtRecord,const char * key)268 int DNSSD_API TXTRecordContainsKey
269 (
270     uint16_t txtLen,
271     const void       *txtRecord,
272     const char       *key
273 )
274 {
275     unsigned long keylen;
276     return (InternalTXTRecordSearch(txtLen, txtRecord, key, &keylen) ? 1 : 0);
277 }
278 
TXTRecordGetValuePtr(uint16_t txtLen,const void * txtRecord,const char * key,uint8_t * valueLen)279 const void * DNSSD_API TXTRecordGetValuePtr
280 (
281     uint16_t txtLen,
282     const void       *txtRecord,
283     const char       *key,
284     uint8_t          *valueLen
285 )
286 {
287     unsigned long keylen;
288     uint8_t *item = InternalTXTRecordSearch(txtLen, txtRecord, key, &keylen);
289     if (!item || item[0] <= keylen) return(NULL);   // If key not found, or found with no value, return NULL
290     *valueLen = (uint8_t)(item[0] - (keylen + 1));
291     return (item + 1 + keylen + 1);
292 }
293 
TXTRecordGetCount(uint16_t txtLen,const void * txtRecord)294 uint16_t DNSSD_API TXTRecordGetCount
295 (
296     uint16_t txtLen,
297     const void       *txtRecord
298 )
299 {
300     uint16_t count = 0;
301     uint8_t *p = (uint8_t*)txtRecord;
302     uint8_t *e = p + txtLen;
303     while (p<e) { p += 1 + p[0]; count++; }
304     return((p>e) ? (uint16_t)0 : count);
305 }
306 
TXTRecordGetItemAtIndex(uint16_t txtLen,const void * txtRecord,uint16_t itemIndex,uint16_t keyBufLen,char * key,uint8_t * valueLen,const void ** value)307 DNSServiceErrorType DNSSD_API TXTRecordGetItemAtIndex
308 (
309     uint16_t txtLen,
310     const void       *txtRecord,
311     uint16_t itemIndex,
312     uint16_t keyBufLen,
313     char             *key,
314     uint8_t          *valueLen,
315     const void       **value
316 )
317 {
318     uint16_t count = 0;
319     uint8_t *p = (uint8_t*)txtRecord;
320     uint8_t *e = p + txtLen;
321     while (p<e && count<itemIndex) { p += 1 + p[0]; count++; }  // Find requested item
322     if (p<e && p + 1 + p[0] <= e)   // If valid
323     {
324         uint8_t *x = p+1;
325         unsigned long len = 0;
326         e = p + 1 + p[0];
327         while (x+len<e && x[len] != '=') len++;
328         if (len >= keyBufLen) return(kDNSServiceErr_NoMemory);
329         memcpy(key, x, len);
330         key[len] = 0;
331         if (x+len<e)        // If we found '='
332         {
333             *value = x + len + 1;
334             *valueLen = (uint8_t)(p[0] - (len + 1));
335         }
336         else
337         {
338             *value = NULL;
339             *valueLen = 0;
340         }
341         return(kDNSServiceErr_NoError);
342     }
343     return(kDNSServiceErr_Invalid);
344 }
345 
346 /*********************************************************************************************
347 *
348 *   SCCS-compatible version string
349 *
350 *********************************************************************************************/
351 
352 // For convenience when using the "strings" command, this is the last thing in the file
353 
354 // Note: The C preprocessor stringify operator ('#') makes a string from its argument, without macro expansion
355 // e.g. If "version" is #define'd to be "4", then STRINGIFY_AWE(version) will return the string "version", not "4"
356 // To expand "version" to its value before making the string, use STRINGIFY(version) instead
357 #define STRINGIFY_ARGUMENT_WITHOUT_EXPANSION(s) # s
358 #define STRINGIFY(s) STRINGIFY_ARGUMENT_WITHOUT_EXPANSION(s)
359 
360 // The "used" variable attribute prevents a non-exported variable from being stripped, even if its visibility is hidden,
361 // e.g., when compiling with -fvisibility=hidden.
362 #if defined(__GNUC__)
363 #define DNSSD_USED __attribute__((used))
364 #else
365 #define DNSSD_USED
366 #endif
367 
368 // NOT static -- otherwise the compiler may optimize it out
369 // The "@(#) " pattern is a special prefix the "what" command looks for
370 #ifndef MDNS_VERSIONSTR_NODTS
371 const char VersionString_SCCS_libdnssd[] DNSSD_USED = "@(#) libdns_sd " STRINGIFY(mDNSResponderVersion) " (" __DATE__ " " __TIME__ ")";
372 #else
373 const char VersionString_SCCS_libdnssd[] = "@(#) libdns_sd " STRINGIFY(mDNSResponderVersion);
374 #endif
375