diff options
Diffstat (limited to 'lib')
| -rw-r--r-- | lib/doh.c | 76 | ||||
| -rw-r--r-- | lib/doh.h | 6 |
2 files changed, 56 insertions, 26 deletions
@@ -86,12 +86,36 @@ UNITTEST DOHcode doh_encode(const char *host, unsigned char *orig = dnsp; const char *hostp = host; - /* The expected output length does not depend on the number of dots within - * the host name. It will always be two more than the length of the host - * name, one for the size and one trailing null. In case there are dots, - * each dot adds one size but removes the need to store the dot, net zero. + /* The expected output length is 16 bytes more than the length of + * the QNAME-encoding of the host name. + * + * A valid DNS name may not contain a zero-length label, except at + * the end. For this reason, a name beginning with a dot, or + * containing a sequence of two or more consecutive dots, is invalid + * and cannot be encoded as a QNAME. + * + * If the host name ends with a trailing dot, the corresponding + * QNAME-encoding is one byte longer than the host name. If (as is + * also valid) the hostname is shortened by the omission of the + * trailing dot, then its QNAME-encoding will be two bytes longer + * than the host name. + * + * Each [ label, dot ] pair is encoded as [ length, label ], + * preserving overall length. A final [ label ] without a dot is + * also encoded as [ length, label ], increasing overall length + * by one. The encoding is completed by appending a zero byte, + * representing the zero-length root label, again increasing + * the overall length by one. */ - const size_t expected_len = 12 + ( 1 + hostlen + 1) + 4; + + size_t expected_len; + DEBUGASSERT(hostlen); + expected_len = 12 + 1 + hostlen + 4; + if(host[hostlen-1]!='.') + expected_len++; + + if(expected_len > (256 + 16)) /* RFCs 1034, 1035 */ + return DOH_DNS_NAME_TOO_LONG; if(len < expected_len) return DOH_TOO_SMALL_BUFFER; @@ -109,31 +133,30 @@ UNITTEST DOHcode doh_encode(const char *host, *dnsp++ = '\0'; *dnsp++ = '\0'; /* ARCOUNT */ - /* store a QNAME */ - do { - char *dot = strchr(hostp, '.'); + /* encode each label and store it in the QNAME */ + while(*hostp) { size_t labellen; - bool found = false; - if(dot) { - found = true; + char *dot = strchr(hostp, '.'); + if(dot) labellen = dot - hostp; - } else labellen = strlen(hostp); - if(labellen > 63) { - /* too long label, error out */ + if((labellen > 63) || (!labellen)) { + /* label is too long or too short, error out */ *olen = 0; return DOH_DNS_BAD_LABEL; } + /* label is non-empty, process it */ *dnsp++ = (unsigned char)labellen; memcpy(dnsp, hostp, labellen); dnsp += labellen; - hostp += labellen + 1; - if(!found) { - *dnsp++ = 0; /* terminating zero */ - break; - } - } while(1); + hostp += labellen; + /* advance past dot, but only if there is one */ + if(dot) + hostp++; + } /* next label */ + + *dnsp++ = 0; /* append zero-length label for root */ /* There are assigned TYPE codes beyond 255: use range [1..65535] */ *dnsp++ = (unsigned char)(255 & (dnstype>>8)); /* upper 8 bit TYPE */ @@ -144,8 +167,8 @@ UNITTEST DOHcode doh_encode(const char *host, *olen = dnsp - orig; - /* verify that our assumption of length is valid, since - * this has lead to buffer overflows in this function */ + /* verify that our estimation of length is valid, since + * this has led to buffer overflows in this function */ DEBUGASSERT(*olen == expected_len); return DOH_OK; } @@ -586,6 +609,9 @@ static DOHcode rdata(unsigned char *doh, if(rc) return rc; break; + case DNS_TYPE_DNAME: + /* explicit for clarity; just skip; rely on synthesized CNAME */ + break; default: /* unsupported type, just skip it */ break; @@ -647,8 +673,10 @@ UNITTEST DOHcode doh_decode(unsigned char *doh, return DOH_DNS_OUT_OF_RANGE; type = get16bit(doh, index); - if((type != DNS_TYPE_CNAME) && (type != dnstype)) - /* Not the same type as was asked for nor CNAME */ + if((type != DNS_TYPE_CNAME) /* may be synthesized from DNAME */ + && (type != DNS_TYPE_DNAME) /* if present, accept and ignore */ + && (type != dnstype)) + /* Not the same type as was asked for nor CNAME nor DNAME */ return DOH_DNS_UNEXPECTED_TYPE; index += 2; @@ -55,14 +55,16 @@ typedef enum { DOH_DNS_UNEXPECTED_TYPE, /* 9 */ DOH_DNS_UNEXPECTED_CLASS, /* 10 */ DOH_NO_CONTENT, /* 11 */ - DOH_DNS_BAD_ID /* 12 */ + DOH_DNS_BAD_ID, /* 12 */ + DOH_DNS_NAME_TOO_LONG /* 13 */ } DOHcode; typedef enum { DNS_TYPE_A = 1, DNS_TYPE_NS = 2, DNS_TYPE_CNAME = 5, - DNS_TYPE_AAAA = 28 + DNS_TYPE_AAAA = 28, + DNS_TYPE_DNAME = 39 /* RFC6672 */ } DNStype; #define DOH_MAX_ADDR 24 |