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authorNiall <Niall.oReilly@ucd.ie>2019-11-14 19:21:09 +0000
committerDaniel Stenberg <daniel@haxx.se>2019-11-16 16:15:03 +0100
commitb6a53fff6c1d07e8a9cb65ca1066d99490fb8132 (patch)
tree8f8b8ee97d9de60d29c0235953b37f798523769b /lib
parent7627a2dd9d4b7417672fdec3dc6e7f8d3de379de (diff)
doh: improced both encoding and decoding
Improved estimation of expected_len and updated related comments; increased strictness of QNAME-encoding, adding error detection for empty labels and names longer than the overall limit; avoided treating DNAME as unexpected; updated unit test 1655 with more thorough set of proofs and tests Closes #4598
Diffstat (limited to 'lib')
-rw-r--r--lib/doh.c76
-rw-r--r--lib/doh.h6
2 files changed, 56 insertions, 26 deletions
diff --git a/lib/doh.c b/lib/doh.c
index d1795789e..73ccce95e 100644
--- a/lib/doh.c
+++ b/lib/doh.c
@@ -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;
diff --git a/lib/doh.h b/lib/doh.h
index f522d3308..fc053eddf 100644
--- a/lib/doh.h
+++ b/lib/doh.h
@@ -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