WIP dns packet en/decoding

diff --git a/dns-transp-common.c b/dns-transp-common.c
new file mode 100644 (file)
index 0000000..59f739a
--- /dev/null
+++ b/dns-transp-common.c
@@ -0,0 +1,193 @@
+
+static const char out_table[32]="0123456789abcdefghijklmnopqrstuv";
+
+static inline int enoughinput(struct dnsbitenc *be) {
+    return be->npending >= 5;
+}
+static inline void startlabel(struct dnsbitenc *be) {
+    be->labremain=63;
+}
+static inline void outputchar(struct dnsbitenc *be) {
+    /* there must be enough input and enough space */
+    if (!be->labremain) {
+       *--(be->out) = 63;
+       startlabel(be);
+    }
+    *--(be->out) = out_table[be->pending & 0x1f];
+    be->pending >>= 5;
+    be->npending -= 5;
+}
+
+void dnsbitenc_start(struct dnsbitenc *be, uint8_t *buf, int buflen) {
+    assert(buflen>0);
+    be->pending=0;
+    be->npending=0;
+    be->bufstop=buf+1;
+    be->out=buf+buflen;
+    startlabel(be);
+}
+
+void dnsbitenc_addbits(struct dnsbitenc *be, uint32_t val, int nbits) {
+    assert(nbits<=28); /* otherwise pending might overflow */
+    assert(!(val & ~(((uint32_t)1 << nbits)-1)));
+    be->pending |= val << be->npending;
+    be->npending += nbits;
+    while (enoughinput(be)) {
+       assert(be->out > be->bufstop);
+       outputchar(be);
+    }
+}
+
+void dnsbitenc_addu32(struct dnsbitenc *be, uint32_t val) {
+    dnsbitenc_addbits(be, val & 0xffff, 16);
+    dnsbitenc_addbits(be, val >> 16,    16);
+}
+
+int dnsbitenc_restbytes(struct dnsbitenc *be, uint8_t *bytes, int qty) {
+    for (;;) {
+       if (buf==bufstop) {
+           return qty + ((be->npending + 7) / 8);
+       }
+       if (be->npending<5) {
+           if (qty) {
+               be->pending |= (*bytes++) << be->npending;
+               be->npending += 8;
+           } else if (be->npending <= 0) {
+               return 0;
+           }
+       }       
+       outputchar(be);
+    }
+}
+
+uint8_t *dnsbitenc_getresult(struct dnsbitenc *be) {
+    *--(be->out) = 63 - be->labremain; /* finish the last label */
+    return be->out;
+}
+
+
+
+
+#define MAX_DATA_LABELS
+
+struct labelinpacket {
+    const uint8_t *bytes;
+    int len;
+};
+
+struct dnsbitdec {
+    /* private for dnsbitdec_... functions; do not access direcctly */
+    const databuf[MAX_DOMAIN_BYTES];
+    const uint8_t *in;
+};
+
+static void setafter(const uint8_t *domain, const uint8_t **domain_end_r) {
+    if (domain_end_r && !*domain_end_r)
+       *domain_end_r=domain;
+}
+
+int dnsdomaindec_start(struct dnsbitdec *bd, const uint8_t *packet,
+                      const uint8_t *endpacket, const uint8_t *domain,
+                      int mydompathlen, const char *mydompath[],
+                      const uint8_t **domain_end_r) {
+    int maxlabels=mydompath+MAX_DATA_LABELS;
+    const strut labelinpacket labels[maxlabels];
+    int nlabels=0, totallen=0;
+
+    *domain_end_r=0;
+    for (;;) {
+       if (domain==endpacket)
+           return FORMERR;
+       unsigned b=*domain++;
+       if (!b) {
+           totallen++;
+           setafter(domain,domain_end_r);
+           break;
+       }
+       if ((b & 0xc0) == 0xc0) {
+           if (domain==endpacket)
+               return FORMERR;
+           unsigned b2=*domain++;
+           setafter(domain,domain_end_r);
+           unsigned off= ((b & 0x3f)<<8) | b2;
+           if (off >= endpacket - packet)
+               return False;
+           domain=packet+off;
+           b=*domain++;
+           if (!b) return FORMERR
+           /* now fall through to code expecting a literal */
+       }
+       if ((b & 0xc0) != 0x00)
+           return FORMERR;
+       if (nlabels>=maxlabels)
+           return NOTAUTH;
+       totallen+=b+1;
+       if (totallen >= MAX_DOMAIN_BYTES) /* we still need a nul label */
+           return FORMERR;
+       labels[nlabels].bytes=domain;
+       labels[nlabels].len=b;
+       nlabels++;
+       domain += b;
+    }
+    if (nlabels <= mydompathlen)
+       return NOTAUTH;
+    for (i=0; i<mydompathlen; i++) {
+       int l=strlen(mydompath[i]);
+       const struct labelinpacket *got=&labels[nlabels-mydompathlen];
+       if (got->len != l || memcmp(got->bytes,mydompath[i]))
+           return NOTAUTH;
+    }
+    /* OK, it's our domain and it has some data and a good
+     * number of labels.  Wow. */
+    uint8_t *copyto=&bd->databuf;
+    for (i=0; i<nlabels-mydompathlen; i++) {
+       const uint8_t *p=labels[i].bytes;
+       for (j=0; j<labels[i].len; j++) {
+           int val=in_table[*p++];
+           if (val & 0x80)
+               return NXDOMAIN;
+           *copyto++=val;
+       }
+    }
+    assert(copyto <= bd->databuf+sizeof(bd->databuf));
+    bd->in=copyto;
+    return 0;
+}
+
+static uint8_t in_table[256];
+
+static void dnsdomaindec_globalinit(void) {
+    memset(in_table,0xff,sizeof(in_table));
+    for (i=0; i<32; i++) {
+       in_table[out_table[i]]=i;
+       in_table[toupper((unsigned char)out_table[i])]=i;
+    }
+}
+
+static void inputchar(struct dnsbitdec *bd) {
+    /* must be enough input and enough space in pending */
+    int ch=*--(bd->in);
+    bd->pending <<= 8;
+    bd->pending |= ch; /* already decoded */
+}
+uint32_t dnsdomaindec_getbits(struct dnsbitdec *bd, int nbits)
+{
+    /* must be enough */
+    assert(nbits<=28);
+    while (bd->pending < nbits)
+       inputchar();
+    int newnpending = bd->pending - nbits;
+    uint32_t rv = bd->pending >> newnpending;
+    bd->pending &= ((uint32_t)1 << newnpending)-1;
+    bd->npending = newnpending;
+}
+uint32_t dnsdomaindec_getu32(struct dnsbitdec *bd)
+{
+    uint32_t lsw=dnsdomaindec_getbits(bd,16);
+    uint32_t msw=dnsdomaindec_getbits(bd,16);
+    return (msw << 16) | lsw;
+}
+int dnsbitdec_restbytes(struct dnsbitdec *bd, uint8_t outbuf[MAX_DOMAIN_BYTES])
+{
+    for (;;) {
+       

diff --git a/dns-transp-common.h b/dns-transp-common.h
new file mode 100644 (file)
index 0000000..a715427
--- /dev/null
+++ b/dns-transp-common.h
@@ -0,0 +1,31 @@
+
+struct dnsbitenc {
+    /* private for dnsbitenc_... functions; do not access direcctly */
+    uint32_t pending;
+    int npending; /* never more than 4 unless we're in the middle */
+    uint8_t *out, *bufstop; /* counts backwards */
+    int labremain;
+};
+
+/*
+ * The only legal calling sequence is this:
+ *   start
+ *   (addbits | addu32)*
+ *   restbytes
+ *   getresult
+ */
+
+void dnsbitenc_start(struct dnsbitenc *be, uint8_t *buf, int buflen);
+
+void dnsbitenc_addbits(struct dnsbitenc *be, uint32_t val, int nbits);
+    /* adds the bottom nbits bits of val; must be enough space; nbits<=28 */
+void dnsbitenc_addu32(struct dnsbitenc *be, uint32_t val);
+    /* must be enough space */
+
+int dnsbitenc_restbytes(struct dnsbitenc *be, uint8_t *bytes, int qty);
+    /* returns number of bytes which did not fit */
+
+uint8_t *dnsbitenc_getresult(struct dnsbitenc *be);
+    /* returns pointer into caller-supplied buffer; we have used
+     * bytes from the result to the end (so the caller needs to remember
+     * the buffer len to know what the encoded length is */

diff --git a/dns-transp-server.c b/dns-transp-server.c
index 154c907bbc08a6727860774dbc0ce16d09c0aa0a..fd52b8a2fc6ddcc51d282efdb48d4d0e532ff7fb 100644 (file)
--- a/dns-transp-server.c
+++ b/dns-transp-server.c
@@ -10,25 +10,25 @@
 
 /*
  * Query format: create assoc:
 
 /*
  * Query format: create assoc:

- *    1 bit set    this a create assoc query

  *   32 bits       clientnonce
  *   32 bits       clientnonce

+ *    1 bit set    this is a create assoc query

  *   10 bits       offset of this data fragment in packet
  *    1 bit        is this the last fragment ?
  *    remainder    data packet fragment
  * data packet sequence number is always implicitly zero
  *
  * Query format: submit:
  *   10 bits       offset of this data fragment in packet
  *    1 bit        is this the last fragment ?
  *    remainder    data packet fragment
  * data packet sequence number is always implicitly zero
  *
  * Query format: submit:

- *    1 bit clear  this is not a create assoc query

  *   32 bits       associd
  *   32 bits       associd

+ *    1 bit clear  this is not a create assoc query

  *   16 bits       data packet sequence number
  *   10 bits       offset of this data fragment in packet
  *    1 bit        is this the last fragment
  *    remainder    data packet fragment
  *
  * Query format: fetch:
  *   16 bits       data packet sequence number
  *   10 bits       offset of this data fragment in packet
  *    1 bit        is this the last fragment
  *    remainder    data packet fragment
  *
  * Query format: fetch:

- *    1 bit clear  this is not a create assoc query

  *   32 bits       associd
  *   32 bits       associd

- *   16 bits       client query distinguishper (for defeating dns cache)
+ *    1 bit clear  this is not a create assoc query
+ *   16 bits       client query distinguisher (for defeating dns cache)

  *
  * Response format:
  * [ 32 bits       associd  - only for responses to create assoc ]
  *
  * Response format:
  * [ 32 bits       associd  - only for responses to create assoc ]


@@ -42,6 +42,15 @@
  * Query bitstring, from above, is encoded as follows:
  *   1. 
  *    . append our server's domain
  * Query bitstring, from above, is encoded as follows:
  *   1. 
  *    . append our server's domain

+ * Max DNS domain is 255 bytes.
+ * Max UDP packet is 512 bytes.
+ * If our domain is     .s.chiark.net.     (12 bytes)
+ * then we have 241 bytes of payload left.
+ * We need at least 4 subdomains to avoid blowing the 63-byte limit
+ * So that means we need 3 more dots, so 238 chars.
+ * At 5 bits per char that's 1190 bits.  Minus our submit
+ * header (1+32+16+10+1 = 60 bits) that's 1130 bits or 141.25 bytes.
+ */

 
 struct expires {
     struct expires *next;
 
 struct expires {
     struct expires *next;