/* * Copyright (C) 2008 The Android Open Source Project * All rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * * Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * * Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in * the documentation and/or other materials provided with the * distribution. * * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. */ #include "resolv_cache.h" #include #include #include #include "pthread.h" #include #include "arpa_nameser.h" /* This code implements a small and *simple* DNS resolver cache. * * It is only used to cache DNS answers for a time defined by the smallest TTL * among the answer records in order to reduce DNS traffic. It is not supposed * to be a full DNS cache, since we plan to implement that in the future in a * dedicated process running on the system. * * Note that its design is kept simple very intentionally, i.e.: * * - it takes raw DNS query packet data as input, and returns raw DNS * answer packet data as output * * (this means that two similar queries that encode the DNS name * differently will be treated distinctly). * * the smallest TTL value among the answer records are used as the time * to keep an answer in the cache. * * this is bad, but we absolutely want to avoid parsing the answer packets * (and should be solved by the later full DNS cache process). * * - the implementation is just a (query-data) => (answer-data) hash table * with a trivial least-recently-used expiration policy. * * Doing this keeps the code simple and avoids to deal with a lot of things * that a full DNS cache is expected to do. * * The API is also very simple: * * - the client calls _resolv_cache_get() to obtain a handle to the cache. * this will initialize the cache on first usage. the result can be NULL * if the cache is disabled. * * - the client calls _resolv_cache_lookup() before performing a query * * if the function returns RESOLV_CACHE_FOUND, a copy of the answer data * has been copied into the client-provided answer buffer. * * if the function returns RESOLV_CACHE_NOTFOUND, the client should perform * a request normally, *then* call _resolv_cache_add() to add the received * answer to the cache. * * if the function returns RESOLV_CACHE_UNSUPPORTED, the client should * perform a request normally, and *not* call _resolv_cache_add() * * note that RESOLV_CACHE_UNSUPPORTED is also returned if the answer buffer * is too short to accomodate the cached result. * * - when network settings change, the cache must be flushed since the list * of DNS servers probably changed. this is done by calling * _resolv_cache_reset() * * the parameter to this function must be an ever-increasing generation * number corresponding to the current network settings state. * * This is done because several threads could detect the same network * settings change (but at different times) and will all end up calling the * same function. Comparing with the last used generation number ensures * that the cache is only flushed once per network change. */ /* the name of an environment variable that will be checked the first time * this code is called if its value is "0", then the resolver cache is * disabled. */ #define CONFIG_ENV "BIONIC_DNSCACHE" /* entries older than CONFIG_SECONDS seconds are always discarded. */ #define CONFIG_SECONDS (60*10) /* 10 minutes */ /* maximum number of entries kept in the cache. This value has been * determined by browsing through various sites and counting the number * of corresponding requests. Keep in mind that our framework is currently * performing two requests per name lookup (one for IPv4, the other for IPv6) * * www.google.com 4 * www.ysearch.com 6 * www.amazon.com 8 * www.nytimes.com 22 * www.espn.com 28 * www.msn.com 28 * www.lemonde.fr 35 * * (determined in 2009-2-17 from Paris, France, results may vary depending * on location) * * most high-level websites use lots of media/ad servers with different names * but these are generally reused when browsing through the site. * * As such, a valud of 64 should be relatively conformtable at the moment. */ #define CONFIG_MAX_ENTRIES 64 /****************************************************************************/ /****************************************************************************/ /***** *****/ /***** *****/ /***** *****/ /****************************************************************************/ /****************************************************************************/ /* set to 1 to debug cache operations */ #define DEBUG 0 /* set to 1 to debug query data */ #define DEBUG_DATA 0 #undef XLOG #if DEBUG # include # define XLOG(...) \ __libc_android_log_print(ANDROID_LOG_DEBUG,"libc",__VA_ARGS__) #include #include #include #include "resolv_private.h" /** BOUNDED BUFFER FORMATTING **/ /* technical note: * * the following debugging routines are used to append data to a bounded * buffer they take two parameters that are: * * - p : a pointer to the current cursor position in the buffer * this value is initially set to the buffer's address. * * - end : the address of the buffer's limit, i.e. of the first byte * after the buffer. this address should never be touched. * * IMPORTANT: it is assumed that end > buffer_address, i.e. * that the buffer is at least one byte. * * the _bprint_() functions return the new value of 'p' after the data * has been appended, and also ensure the following: * * - the returned value will never be strictly greater than 'end' * * - a return value equal to 'end' means that truncation occured * (in which case, end[-1] will be set to 0) * * - after returning from a _bprint_() function, the content of the buffer * is always 0-terminated, even in the event of truncation. * * these conventions allow you to call _bprint_ functions multiple times and * only check for truncation at the end of the sequence, as in: * * char buff[1000], *p = buff, *end = p + sizeof(buff); * * p = _bprint_c(p, end, '"'); * p = _bprint_s(p, end, my_string); * p = _bprint_c(p, end, '"'); * * if (p >= end) { * // buffer was too small * } * * printf( "%s", buff ); */ /* add a char to a bounded buffer */ static char* _bprint_c( char* p, char* end, int c ) { if (p < end) { if (p+1 == end) *p++ = 0; else { *p++ = (char) c; *p = 0; } } return p; } /* add a sequence of bytes to a bounded buffer */ static char* _bprint_b( char* p, char* end, const char* buf, int len ) { int avail = end - p; if (avail <= 0 || len <= 0) return p; if (avail > len) avail = len; memcpy( p, buf, avail ); p += avail; if (p < end) p[0] = 0; else end[-1] = 0; return p; } /* add a string to a bounded buffer */ static char* _bprint_s( char* p, char* end, const char* str ) { return _bprint_b(p, end, str, strlen(str)); } /* add a formatted string to a bounded buffer */ static char* _bprint( char* p, char* end, const char* format, ... ) { int avail, n; va_list args; avail = end - p; if (avail <= 0) return p; va_start(args, format); n = vsnprintf( p, avail, format, args); va_end(args); /* certain C libraries return -1 in case of truncation */ if (n < 0 || n > avail) n = avail; p += n; /* certain C libraries do not zero-terminate in case of truncation */ if (p == end) p[-1] = 0; return p; } /* add a hex value to a bounded buffer, up to 8 digits */ static char* _bprint_hex( char* p, char* end, unsigned value, int numDigits ) { char text[sizeof(unsigned)*2]; int nn = 0; while (numDigits-- > 0) { text[nn++] = "0123456789abcdef"[(value >> (numDigits*4)) & 15]; } return _bprint_b(p, end, text, nn); } /* add the hexadecimal dump of some memory area to a bounded buffer */ static char* _bprint_hexdump( char* p, char* end, const uint8_t* data, int datalen ) { int lineSize = 16; while (datalen > 0) { int avail = datalen; int nn; if (avail > lineSize) avail = lineSize; for (nn = 0; nn < avail; nn++) { if (nn > 0) p = _bprint_c(p, end, ' '); p = _bprint_hex(p, end, data[nn], 2); } for ( ; nn < lineSize; nn++ ) { p = _bprint_s(p, end, " "); } p = _bprint_s(p, end, " "); for (nn = 0; nn < avail; nn++) { int c = data[nn]; if (c < 32 || c > 127) c = '.'; p = _bprint_c(p, end, c); } p = _bprint_c(p, end, '\n'); data += avail; datalen -= avail; } return p; } /* dump the content of a query of packet to the log */ static void XLOG_BYTES( const void* base, int len ) { char buff[1024]; char* p = buff, *end = p + sizeof(buff); p = _bprint_hexdump(p, end, base, len); XLOG("%s",buff); } #else /* !DEBUG */ # define XLOG(...) ((void)0) # define XLOG_BYTES(a,b) ((void)0) #endif static time_t _time_now( void ) { struct timeval tv; gettimeofday( &tv, NULL ); return tv.tv_sec; } /* reminder: the general format of a DNS packet is the following: * * HEADER (12 bytes) * QUESTION (variable) * ANSWER (variable) * AUTHORITY (variable) * ADDITIONNAL (variable) * * the HEADER is made of: * * ID : 16 : 16-bit unique query identification field * * QR : 1 : set to 0 for queries, and 1 for responses * Opcode : 4 : set to 0 for queries * AA : 1 : set to 0 for queries * TC : 1 : truncation flag, will be set to 0 in queries * RD : 1 : recursion desired * * RA : 1 : recursion available (0 in queries) * Z : 3 : three reserved zero bits * RCODE : 4 : response code (always 0=NOERROR in queries) * * QDCount: 16 : question count * ANCount: 16 : Answer count (0 in queries) * NSCount: 16: Authority Record count (0 in queries) * ARCount: 16: Additionnal Record count (0 in queries) * * the QUESTION is made of QDCount Question Record (QRs) * the ANSWER is made of ANCount RRs * the AUTHORITY is made of NSCount RRs * the ADDITIONNAL is made of ARCount RRs * * Each Question Record (QR) is made of: * * QNAME : variable : Query DNS NAME * TYPE : 16 : type of query (A=1, PTR=12, MX=15, AAAA=28, ALL=255) * CLASS : 16 : class of query (IN=1) * * Each Resource Record (RR) is made of: * * NAME : variable : DNS NAME * TYPE : 16 : type of query (A=1, PTR=12, MX=15, AAAA=28, ALL=255) * CLASS : 16 : class of query (IN=1) * TTL : 32 : seconds to cache this RR (0=none) * RDLENGTH: 16 : size of RDDATA in bytes * RDDATA : variable : RR data (depends on TYPE) * * Each QNAME contains a domain name encoded as a sequence of 'labels' * terminated by a zero. Each label has the following format: * * LEN : 8 : lenght of label (MUST be < 64) * NAME : 8*LEN : label length (must exclude dots) * * A value of 0 in the encoding is interpreted as the 'root' domain and * terminates the encoding. So 'www.android.com' will be encoded as: * * <3>www<7>android<3>com<0> * * Where represents the byte with value 'n' * * Each NAME reflects the QNAME of the question, but has a slightly more * complex encoding in order to provide message compression. This is achieved * by using a 2-byte pointer, with format: * * TYPE : 2 : 0b11 to indicate a pointer, 0b01 and 0b10 are reserved * OFFSET : 14 : offset to another part of the DNS packet * * The offset is relative to the start of the DNS packet and must point * A pointer terminates the encoding. * * The NAME can be encoded in one of the following formats: * * - a sequence of simple labels terminated by 0 (like QNAMEs) * - a single pointer * - a sequence of simple labels terminated by a pointer * * A pointer shall always point to either a pointer of a sequence of * labels (which can themselves be terminated by either a 0 or a pointer) * * The expanded length of a given domain name should not exceed 255 bytes. * * NOTE: we don't parse the answer packets, so don't need to deal with NAME * records, only QNAMEs. */ #define DNS_HEADER_SIZE 12 #define DNS_TYPE_A "\00\01" /* big-endian decimal 1 */ #define DNS_TYPE_PTR "\00\014" /* big-endian decimal 12 */ #define DNS_TYPE_MX "\00\017" /* big-endian decimal 15 */ #define DNS_TYPE_AAAA "\00\034" /* big-endian decimal 28 */ #define DNS_TYPE_ALL "\00\0377" /* big-endian decimal 255 */ #define DNS_CLASS_IN "\00\01" /* big-endian decimal 1 */ typedef struct { const uint8_t* base; const uint8_t* end; const uint8_t* cursor; } DnsPacket; static void _dnsPacket_init( DnsPacket* packet, const uint8_t* buff, int bufflen ) { packet->base = buff; packet->end = buff + bufflen; packet->cursor = buff; } static void _dnsPacket_rewind( DnsPacket* packet ) { packet->cursor = packet->base; } static void _dnsPacket_skip( DnsPacket* packet, int count ) { const uint8_t* p = packet->cursor + count; if (p > packet->end) p = packet->end; packet->cursor = p; } static int _dnsPacket_readInt16( DnsPacket* packet ) { const uint8_t* p = packet->cursor; if (p+2 > packet->end) return -1; packet->cursor = p+2; return (p[0]<< 8) | p[1]; } /** QUERY CHECKING **/ /* check bytes in a dns packet. returns 1 on success, 0 on failure. * the cursor is only advanced in the case of success */ static int _dnsPacket_checkBytes( DnsPacket* packet, int numBytes, const void* bytes ) { const uint8_t* p = packet->cursor; if (p + numBytes > packet->end) return 0; if (memcmp(p, bytes, numBytes) != 0) return 0; packet->cursor = p + numBytes; return 1; } /* parse and skip a given QNAME stored in a query packet, * from the current cursor position. returns 1 on success, * or 0 for malformed data. */ static int _dnsPacket_checkQName( DnsPacket* packet ) { const uint8_t* p = packet->cursor; const uint8_t* end = packet->end; for (;;) { int c; if (p >= end) break; c = *p++; if (c == 0) { packet->cursor = p; return 1; } /* we don't expect label compression in QNAMEs */ if (c >= 64) break; p += c; /* we rely on the bound check at the start * of the loop here */ } /* malformed data */ XLOG("malformed QNAME"); return 0; } /* parse and skip a given QR stored in a packet. * returns 1 on success, and 0 on failure */ static int _dnsPacket_checkQR( DnsPacket* packet ) { int len; if (!_dnsPacket_checkQName(packet)) return 0; /* TYPE must be one of the things we support */ if (!_dnsPacket_checkBytes(packet, 2, DNS_TYPE_A) && !_dnsPacket_checkBytes(packet, 2, DNS_TYPE_PTR) && !_dnsPacket_checkBytes(packet, 2, DNS_TYPE_MX) && !_dnsPacket_checkBytes(packet, 2, DNS_TYPE_AAAA) && !_dnsPacket_checkBytes(packet, 2, DNS_TYPE_ALL)) { XLOG("unsupported TYPE"); return 0; } /* CLASS must be IN */ if (!_dnsPacket_checkBytes(packet, 2, DNS_CLASS_IN)) { XLOG("unsupported CLASS"); return 0; } return 1; } /* check the header of a DNS Query packet, return 1 if it is one * type of query we can cache, or 0 otherwise */ static int _dnsPacket_checkQuery( DnsPacket* packet ) { const uint8_t* p = packet->base; int qdCount, anCount, dnCount, arCount; if (p + DNS_HEADER_SIZE > packet->end) { XLOG("query packet too small"); return 0; } /* QR must be set to 0, opcode must be 0 and AA must be 0 */ /* RA, Z, and RCODE must be 0 */ if ((p[2] & 0xFC) != 0 || p[3] != 0) { XLOG("query packet flags unsupported"); return 0; } /* Note that we ignore the TC and RD bits here for the * following reasons: * * - there is no point for a query packet sent to a server * to have the TC bit set, but the implementation might * set the bit in the query buffer for its own needs * between a _resolv_cache_lookup and a * _resolv_cache_add. We should not freak out if this * is the case. * * - we consider that the result from a RD=0 or a RD=1 * query might be different, hence that the RD bit * should be used to differentiate cached result. * * this implies that RD is checked when hashing or * comparing query packets, but not TC */ /* ANCOUNT, DNCOUNT and ARCOUNT must be 0 */ qdCount = (p[4] << 8) | p[5]; anCount = (p[6] << 8) | p[7]; dnCount = (p[8] << 8) | p[9]; arCount = (p[10]<< 8) | p[11]; if (anCount != 0 || dnCount != 0 || arCount != 0) { XLOG("query packet contains non-query records"); return 0; } if (qdCount == 0) { XLOG("query packet doesn't contain query record"); return 0; } /* Check QDCOUNT QRs */ packet->cursor = p + DNS_HEADER_SIZE; for (;qdCount > 0; qdCount--) if (!_dnsPacket_checkQR(packet)) return 0; return 1; } /** QUERY DEBUGGING **/ #if DEBUG static char* _dnsPacket_bprintQName(DnsPacket* packet, char* bp, char* bend) { const uint8_t* p = packet->cursor; const uint8_t* end = packet->end; int first = 1; for (;;) { int c; if (p >= end) break; c = *p++; if (c == 0) { packet->cursor = p; return bp; } /* we don't expect label compression in QNAMEs */ if (c >= 64) break; if (first) first = 0; else bp = _bprint_c(bp, bend, '.'); bp = _bprint_b(bp, bend, (const char*)p, c); p += c; /* we rely on the bound check at the start * of the loop here */ } /* malformed data */ bp = _bprint_s(bp, bend, ""); return bp; } static char* _dnsPacket_bprintQR(DnsPacket* packet, char* p, char* end) { #define QQ(x) { DNS_TYPE_##x, #x } static const struct { const char* typeBytes; const char* typeString; } qTypes[] = { QQ(A), QQ(PTR), QQ(MX), QQ(AAAA), QQ(ALL), { NULL, NULL } }; int nn; const char* typeString = NULL; /* dump QNAME */ p = _dnsPacket_bprintQName(packet, p, end); /* dump TYPE */ p = _bprint_s(p, end, " ("); for (nn = 0; qTypes[nn].typeBytes != NULL; nn++) { if (_dnsPacket_checkBytes(packet, 2, qTypes[nn].typeBytes)) { typeString = qTypes[nn].typeString; break; } } if (typeString != NULL) p = _bprint_s(p, end, typeString); else { int typeCode = _dnsPacket_readInt16(packet); p = _bprint(p, end, "UNKNOWN-%d", typeCode); } p = _bprint_c(p, end, ')'); /* skip CLASS */ _dnsPacket_skip(packet, 2); return p; } /* this function assumes the packet has already been checked */ static char* _dnsPacket_bprintQuery( DnsPacket* packet, char* p, char* end ) { int qdCount; if (packet->base[2] & 0x1) { p = _bprint_s(p, end, "RECURSIVE "); } _dnsPacket_skip(packet, 4); qdCount = _dnsPacket_readInt16(packet); _dnsPacket_skip(packet, 6); for ( ; qdCount > 0; qdCount-- ) { p = _dnsPacket_bprintQR(packet, p, end); } return p; } #endif /** QUERY HASHING SUPPORT ** ** THE FOLLOWING CODE ASSUMES THAT THE INPUT PACKET HAS ALREADY ** BEEN SUCCESFULLY CHECKED. **/ /* use 32-bit FNV hash function */ #define FNV_MULT 16777619U #define FNV_BASIS 2166136261U static unsigned _dnsPacket_hashBytes( DnsPacket* packet, int numBytes, unsigned hash ) { const uint8_t* p = packet->cursor; const uint8_t* end = packet->end; while (numBytes > 0 && p < end) { hash = hash*FNV_MULT ^ *p++; } packet->cursor = p; return hash; } static unsigned _dnsPacket_hashQName( DnsPacket* packet, unsigned hash ) { const uint8_t* p = packet->cursor; const uint8_t* end = packet->end; for (;;) { int c; if (p >= end) { /* should not happen */ XLOG("%s: INTERNAL_ERROR: read-overflow !!\n", __FUNCTION__); break; } c = *p++; if (c == 0) break; if (c >= 64) { XLOG("%s: INTERNAL_ERROR: malformed domain !!\n", __FUNCTION__); break; } if (p + c >= end) { XLOG("%s: INTERNAL_ERROR: simple label read-overflow !!\n", __FUNCTION__); break; } while (c > 0) { hash = hash*FNV_MULT ^ *p++; c -= 1; } } packet->cursor = p; return hash; } static unsigned _dnsPacket_hashQR( DnsPacket* packet, unsigned hash ) { int len; hash = _dnsPacket_hashQName(packet, hash); hash = _dnsPacket_hashBytes(packet, 4, hash); /* TYPE and CLASS */ return hash; } static unsigned _dnsPacket_hashQuery( DnsPacket* packet ) { unsigned hash = FNV_BASIS; int count; _dnsPacket_rewind(packet); /* we ignore the TC bit for reasons explained in * _dnsPacket_checkQuery(). * * however we hash the RD bit to differentiate * between answers for recursive and non-recursive * queries. */ hash = hash*FNV_MULT ^ (packet->base[2] & 1); /* assume: other flags are 0 */ _dnsPacket_skip(packet, 4); /* read QDCOUNT */ count = _dnsPacket_readInt16(packet); /* assume: ANcount, NScount, ARcount are 0 */ _dnsPacket_skip(packet, 6); /* hash QDCOUNT QRs */ for ( ; count > 0; count-- ) hash = _dnsPacket_hashQR(packet, hash); return hash; } /** QUERY COMPARISON ** ** THE FOLLOWING CODE ASSUMES THAT THE INPUT PACKETS HAVE ALREADY ** BEEN SUCCESFULLY CHECKED. **/ static int _dnsPacket_isEqualDomainName( DnsPacket* pack1, DnsPacket* pack2 ) { const uint8_t* p1 = pack1->cursor; const uint8_t* end1 = pack1->end; const uint8_t* p2 = pack2->cursor; const uint8_t* end2 = pack2->end; for (;;) { int c1, c2; if (p1 >= end1 || p2 >= end2) { XLOG("%s: INTERNAL_ERROR: read-overflow !!\n", __FUNCTION__); break; } c1 = *p1++; c2 = *p2++; if (c1 != c2) break; if (c1 == 0) { pack1->cursor = p1; pack2->cursor = p2; return 1; } if (c1 >= 64) { XLOG("%s: INTERNAL_ERROR: malformed domain !!\n", __FUNCTION__); break; } if ((p1+c1 > end1) || (p2+c1 > end2)) { XLOG("%s: INTERNAL_ERROR: simple label read-overflow !!\n", __FUNCTION__); break; } if (memcmp(p1, p2, c1) != 0) break; p1 += c1; p2 += c1; /* we rely on the bound checks at the start of the loop */ } /* not the same, or one is malformed */ XLOG("different DN"); return 0; } static int _dnsPacket_isEqualBytes( DnsPacket* pack1, DnsPacket* pack2, int numBytes ) { const uint8_t* p1 = pack1->cursor; const uint8_t* p2 = pack2->cursor; if ( p1 + numBytes > pack1->end || p2 + numBytes > pack2->end ) return 0; if ( memcmp(p1, p2, numBytes) != 0 ) return 0; pack1->cursor += numBytes; pack2->cursor += numBytes; return 1; } static int _dnsPacket_isEqualQR( DnsPacket* pack1, DnsPacket* pack2 ) { /* compare domain name encoding + TYPE + CLASS */ if ( !_dnsPacket_isEqualDomainName(pack1, pack2) || !_dnsPacket_isEqualBytes(pack1, pack2, 2+2) ) return 0; return 1; } static int _dnsPacket_isEqualQuery( DnsPacket* pack1, DnsPacket* pack2 ) { int count1, count2; /* compare the headers, ignore most fields */ _dnsPacket_rewind(pack1); _dnsPacket_rewind(pack2); /* compare RD, ignore TC, see comment in _dnsPacket_checkQuery */ if ((pack1->base[2] & 1) != (pack2->base[2] & 1)) { XLOG("different RD"); return 0; } /* assume: other flags are all 0 */ _dnsPacket_skip(pack1, 4); _dnsPacket_skip(pack2, 4); /* compare QDCOUNT */ count1 = _dnsPacket_readInt16(pack1); count2 = _dnsPacket_readInt16(pack2); if (count1 != count2 || count1 < 0) { XLOG("different QDCOUNT"); return 0; } /* assume: ANcount, NScount and ARcount are all 0 */ _dnsPacket_skip(pack1, 6); _dnsPacket_skip(pack2, 6); /* compare the QDCOUNT QRs */ for ( ; count1 > 0; count1-- ) { if (!_dnsPacket_isEqualQR(pack1, pack2)) { XLOG("different QR"); return 0; } } return 1; } /****************************************************************************/ /****************************************************************************/ /***** *****/ /***** *****/ /***** *****/ /****************************************************************************/ /****************************************************************************/ /* cache entry. for simplicity, 'hash' and 'hlink' are inlined in this * structure though they are conceptually part of the hash table. * * similarly, mru_next and mru_prev are part of the global MRU list */ typedef struct Entry { unsigned int hash; /* hash value */ struct Entry* hlink; /* next in collision chain */ struct Entry* mru_prev; struct Entry* mru_next; const uint8_t* query; int querylen; const uint8_t* answer; int answerlen; time_t expires; /* time_t when the entry isn't valid any more */ int id; /* for debugging purpose */ } Entry; /** * Parse the answer records and find the smallest * TTL among the answer records. * * The returned TTL is the number of seconds to * keep the answer in the cache. * * In case of parse error zero (0) is returned which * indicates that the answer shall not be cached. */ static u_long answer_getTTL(const void* answer, int answerlen) { ns_msg handle; int ancount, n; u_long result, ttl; ns_rr rr; result = 0; if (ns_initparse(answer, answerlen, &handle) >= 0) { // get number of answer records ancount = ns_msg_count(handle, ns_s_an); for (n = 0; n < ancount; n++) { if (ns_parserr(&handle, ns_s_an, n, &rr) == 0) { ttl = ns_rr_ttl(rr); if (n == 0 || ttl < result) { result = ttl; } } else { XLOG("ns_parserr failed ancount no = %d. errno = %s\n", n, strerror(errno)); } } } else { XLOG("ns_parserr failed. %s\n", strerror(errno)); } XLOG("TTL = %d\n", result); return result; } static void entry_free( Entry* e ) { /* everything is allocated in a single memory block */ if (e) { free(e); } } static __inline__ void entry_mru_remove( Entry* e ) { e->mru_prev->mru_next = e->mru_next; e->mru_next->mru_prev = e->mru_prev; } static __inline__ void entry_mru_add( Entry* e, Entry* list ) { Entry* first = list->mru_next; e->mru_next = first; e->mru_prev = list; list->mru_next = e; first->mru_prev = e; } /* compute the hash of a given entry, this is a hash of most * data in the query (key) */ static unsigned entry_hash( const Entry* e ) { DnsPacket pack[1]; _dnsPacket_init(pack, e->query, e->querylen); return _dnsPacket_hashQuery(pack); } /* initialize an Entry as a search key, this also checks the input query packet * returns 1 on success, or 0 in case of unsupported/malformed data */ static int entry_init_key( Entry* e, const void* query, int querylen ) { DnsPacket pack[1]; memset(e, 0, sizeof(*e)); e->query = query; e->querylen = querylen; e->hash = entry_hash(e); _dnsPacket_init(pack, query, querylen); return _dnsPacket_checkQuery(pack); } /* allocate a new entry as a cache node */ static Entry* entry_alloc( const Entry* init, const void* answer, int answerlen ) { Entry* e; int size; size = sizeof(*e) + init->querylen + answerlen; e = calloc(size, 1); if (e == NULL) return e; e->hash = init->hash; e->query = (const uint8_t*)(e+1); e->querylen = init->querylen; memcpy( (char*)e->query, init->query, e->querylen ); e->answer = e->query + e->querylen; e->answerlen = answerlen; memcpy( (char*)e->answer, answer, e->answerlen ); return e; } static int entry_equals( const Entry* e1, const Entry* e2 ) { DnsPacket pack1[1], pack2[1]; if (e1->querylen != e2->querylen) { return 0; } _dnsPacket_init(pack1, e1->query, e1->querylen); _dnsPacket_init(pack2, e2->query, e2->querylen); return _dnsPacket_isEqualQuery(pack1, pack2); } /****************************************************************************/ /****************************************************************************/ /***** *****/ /***** *****/ /***** *****/ /****************************************************************************/ /****************************************************************************/ /* We use a simple hash table with external collision lists * for simplicity, the hash-table fields 'hash' and 'hlink' are * inlined in the Entry structure. */ #define MAX_HASH_ENTRIES (2*CONFIG_MAX_ENTRIES) typedef struct resolv_cache { int num_entries; Entry mru_list; pthread_mutex_t lock; unsigned generation; int last_id; Entry* entries[ MAX_HASH_ENTRIES ]; } Cache; #define HTABLE_VALID(x) ((x) != NULL && (x) != HTABLE_DELETED) static void _cache_flush_locked( Cache* cache ) { int nn; time_t now = _time_now(); for (nn = 0; nn < MAX_HASH_ENTRIES; nn++) { Entry** pnode = &cache->entries[nn]; while (*pnode != NULL) { Entry* node = *pnode; *pnode = node->hlink; entry_free(node); } } cache->mru_list.mru_next = cache->mru_list.mru_prev = &cache->mru_list; cache->num_entries = 0; cache->last_id = 0; XLOG("*************************\n" "*** DNS CACHE FLUSHED ***\n" "*************************"); } static struct resolv_cache* _resolv_cache_create( void ) { struct resolv_cache* cache; cache = calloc(sizeof(*cache), 1); if (cache) { cache->generation = ~0U; pthread_mutex_init( &cache->lock, NULL ); cache->mru_list.mru_prev = cache->mru_list.mru_next = &cache->mru_list; XLOG("%s: cache created\n", __FUNCTION__); } return cache; } #if DEBUG static void _dump_query( const uint8_t* query, int querylen ) { char temp[256], *p=temp, *end=p+sizeof(temp); DnsPacket pack[1]; _dnsPacket_init(pack, query, querylen); p = _dnsPacket_bprintQuery(pack, p, end); XLOG("QUERY: %s", temp); } static void _cache_dump_mru( Cache* cache ) { char temp[512], *p=temp, *end=p+sizeof(temp); Entry* e; p = _bprint(temp, end, "MRU LIST (%2d): ", cache->num_entries); for (e = cache->mru_list.mru_next; e != &cache->mru_list; e = e->mru_next) p = _bprint(p, end, " %d", e->id); XLOG("%s", temp); } static void _dump_answer(const void* answer, int answerlen) { res_state statep; FILE* fp; char* buf; int fileLen; fp = fopen("/data/reslog.txt", "w+"); if (fp != NULL) { statep = __res_get_state(); res_pquery(statep, answer, answerlen, fp); //Get file length fseek(fp, 0, SEEK_END); fileLen=ftell(fp); fseek(fp, 0, SEEK_SET); buf = (char *)malloc(fileLen+1); if (buf != NULL) { //Read file contents into buffer fread(buf, fileLen, 1, fp); XLOG("%s\n", buf); free(buf); } fclose(fp); remove("/data/reslog.txt"); } else { XLOG("_dump_answer: can't open file\n"); } } #endif #if DEBUG # define XLOG_QUERY(q,len) _dump_query((q), (len)) # define XLOG_ANSWER(a, len) _dump_answer((a), (len)) #else # define XLOG_QUERY(q,len) ((void)0) # define XLOG_ANSWER(a,len) ((void)0) #endif /* This function tries to find a key within the hash table * In case of success, it will return a *pointer* to the hashed key. * In case of failure, it will return a *pointer* to NULL * * So, the caller must check '*result' to check for success/failure. * * The main idea is that the result can later be used directly in * calls to _resolv_cache_add or _resolv_cache_remove as the 'lookup' * parameter. This makes the code simpler and avoids re-searching * for the key position in the htable. * * The result of a lookup_p is only valid until you alter the hash * table. */ static Entry** _cache_lookup_p( Cache* cache, Entry* key ) { int index = key->hash % MAX_HASH_ENTRIES; Entry** pnode = &cache->entries[ key->hash % MAX_HASH_ENTRIES ]; while (*pnode != NULL) { Entry* node = *pnode; if (node == NULL) break; if (node->hash == key->hash && entry_equals(node, key)) break; pnode = &node->hlink; } return pnode; } /* Add a new entry to the hash table. 'lookup' must be the * result of an immediate previous failed _lookup_p() call * (i.e. with *lookup == NULL), and 'e' is the pointer to the * newly created entry */ static void _cache_add_p( Cache* cache, Entry** lookup, Entry* e ) { *lookup = e; e->id = ++cache->last_id; entry_mru_add(e, &cache->mru_list); cache->num_entries += 1; XLOG("%s: entry %d added (count=%d)", __FUNCTION__, e->id, cache->num_entries); } /* Remove an existing entry from the hash table, * 'lookup' must be the result of an immediate previous * and succesful _lookup_p() call. */ static void _cache_remove_p( Cache* cache, Entry** lookup ) { Entry* e = *lookup; XLOG("%s: entry %d removed (count=%d)", __FUNCTION__, e->id, cache->num_entries-1); entry_mru_remove(e); *lookup = e->hlink; entry_free(e); cache->num_entries -= 1; } /* Remove the oldest entry from the hash table. */ static void _cache_remove_oldest( Cache* cache ) { Entry* oldest = cache->mru_list.mru_prev; Entry** lookup = _cache_lookup_p(cache, oldest); if (*lookup == NULL) { /* should not happen */ XLOG("%s: OLDEST NOT IN HTABLE ?", __FUNCTION__); return; } _cache_remove_p(cache, lookup); } ResolvCacheStatus _resolv_cache_lookup( struct resolv_cache* cache, const void* query, int querylen, void* answer, int answersize, int *answerlen ) { DnsPacket pack[1]; Entry key[1]; int index; Entry** lookup; Entry* e; time_t now; ResolvCacheStatus result = RESOLV_CACHE_NOTFOUND; XLOG("%s: lookup", __FUNCTION__); XLOG_QUERY(query, querylen); /* we don't cache malformed queries */ if (!entry_init_key(key, query, querylen)) { XLOG("%s: unsupported query", __FUNCTION__); return RESOLV_CACHE_UNSUPPORTED; } /* lookup cache */ pthread_mutex_lock( &cache->lock ); /* see the description of _lookup_p to understand this. * the function always return a non-NULL pointer. */ lookup = _cache_lookup_p(cache, key); e = *lookup; if (e == NULL) { XLOG( "NOT IN CACHE"); goto Exit; } now = _time_now(); /* remove stale entries here */ if (now >= e->expires) { XLOG( " NOT IN CACHE (STALE ENTRY %p DISCARDED)", *lookup ); _cache_remove_p(cache, lookup); goto Exit; } *answerlen = e->answerlen; if (e->answerlen > answersize) { /* NOTE: we return UNSUPPORTED if the answer buffer is too short */ result = RESOLV_CACHE_UNSUPPORTED; XLOG(" ANSWER TOO LONG"); goto Exit; } memcpy( answer, e->answer, e->answerlen ); /* bump up this entry to the top of the MRU list */ if (e != cache->mru_list.mru_next) { entry_mru_remove( e ); entry_mru_add( e, &cache->mru_list ); } XLOG( "FOUND IN CACHE entry=%p", e ); result = RESOLV_CACHE_FOUND; Exit: pthread_mutex_unlock( &cache->lock ); return result; } void _resolv_cache_add( struct resolv_cache* cache, const void* query, int querylen, const void* answer, int answerlen ) { Entry key[1]; Entry* e; Entry** lookup; u_long ttl; /* don't assume that the query has already been cached */ if (!entry_init_key( key, query, querylen )) { XLOG( "%s: passed invalid query ?", __FUNCTION__); return; } pthread_mutex_lock( &cache->lock ); XLOG( "%s: query:", __FUNCTION__ ); XLOG_QUERY(query,querylen); XLOG_ANSWER(answer, answerlen); #if DEBUG_DATA XLOG( "answer:"); XLOG_BYTES(answer,answerlen); #endif lookup = _cache_lookup_p(cache, key); e = *lookup; if (e != NULL) { /* should not happen */ XLOG("%s: ALREADY IN CACHE (%p) ? IGNORING ADD", __FUNCTION__, e); goto Exit; } if (cache->num_entries >= CONFIG_MAX_ENTRIES) { _cache_remove_oldest(cache); /* need to lookup again */ lookup = _cache_lookup_p(cache, key); e = *lookup; if (e != NULL) { XLOG("%s: ALREADY IN CACHE (%p) ? IGNORING ADD", __FUNCTION__, e); goto Exit; } } ttl = answer_getTTL(answer, answerlen); if (ttl > 0) { e = entry_alloc(key, answer, answerlen); if (e != NULL) { e->expires = ttl + _time_now(); _cache_add_p(cache, lookup, e); } } #if DEBUG _cache_dump_mru(cache); #endif Exit: pthread_mutex_unlock( &cache->lock ); } /****************************************************************************/ /****************************************************************************/ /***** *****/ /***** *****/ /***** *****/ /****************************************************************************/ /****************************************************************************/ static struct resolv_cache* _res_cache; static pthread_once_t _res_cache_once; static void _res_cache_init( void ) { const char* env = getenv(CONFIG_ENV); if (env && atoi(env) == 0) { /* the cache is disabled */ return; } _res_cache = _resolv_cache_create(); } struct resolv_cache* __get_res_cache( void ) { pthread_once( &_res_cache_once, _res_cache_init ); return _res_cache; } void _resolv_cache_reset( unsigned generation ) { XLOG("%s: generation=%d", __FUNCTION__, generation); if (_res_cache == NULL) return; pthread_mutex_lock( &_res_cache->lock ); if (_res_cache->generation != generation) { _cache_flush_locked(_res_cache); _res_cache->generation = generation; } pthread_mutex_unlock( &_res_cache->lock ); }