Harden dnsdb against crafted DNS responses. Bug 3033

(cherry picked from commit 8787c8994f07c23c3664d76926e02f07314d699d)

diff --git a/doc/doc-txt/ChangeLog b/doc/doc-txt/ChangeLog
index c36718d7efeab21ea28d542ab21f47790442208e..f7ab3c00591c777392e851934dc92f17ab3f8769 100644 (file)
--- a/doc/doc-txt/ChangeLog
+++ b/doc/doc-txt/ChangeLog
@@ -225,6 +225,9 @@ JH/39 Bug 3023: Fix crash induced by some combinations of zero-length strings
 JH/40 Support list of dkim results in the dkim_status ACL condition, making
       it more usable in the data ACL.
 
 JH/40 Support list of dkim results in the dkim_status ACL condition, making
       it more usable in the data ACL.
 

+JH/43 Bug 3033: Harden dnsdb lookups against crafted DNS responses.
+      CVE-2023-42219
+

 
 Exim version 4.96
 -----------------
 
 Exim version 4.96
 -----------------

diff --git a/src/src/dns.c b/src/src/dns.c
index 7d7ee0c0460584022028723c4f09a381908a597a..8dc3695a118782926b1ec994997f2dfc420a5acb 100644 (file)
--- a/src/src/dns.c
+++ b/src/src/dns.c
@@ -304,7 +304,7 @@ Return: TRUE for a bad result
 static BOOL
 dnss_inc_aptr(const dns_answer * dnsa, dns_scan * dnss, unsigned delta)
 {
 static BOOL
 dnss_inc_aptr(const dns_answer * dnsa, dns_scan * dnss, unsigned delta)
 {

-return (dnss->aptr += delta) >= dnsa->answer + dnsa->answerlen;
+return (dnss->aptr += delta) > dnsa->answer + dnsa->answerlen;

 }
 
 /*************************************************
 }
 
 /*************************************************


@@ -388,7 +388,7 @@ if (reset != RESET_NEXT)
       TRACE trace = "A-hdr";
       if (dnss_inc_aptr(dnsa, dnss, namelen+8)) goto null_return;
       GETSHORT(dnss->srr.size, dnss->aptr); /* size of data portion */
       TRACE trace = "A-hdr";
       if (dnss_inc_aptr(dnsa, dnss, namelen+8)) goto null_return;
       GETSHORT(dnss->srr.size, dnss->aptr); /* size of data portion */

-      /* skip over it */
+      /* skip over it, checking for a bogus size */

       TRACE trace = "A-skip";
       if (dnss_inc_aptr(dnsa, dnss, dnss->srr.size)) goto null_return;
       }
       TRACE trace = "A-skip";
       if (dnss_inc_aptr(dnsa, dnss, dnss->srr.size)) goto null_return;
       }


@@ -428,10 +428,9 @@ GETLONG(dnss->srr.ttl, dnss->aptr);                /* TTL */
 GETSHORT(dnss->srr.size, dnss->aptr);          /* Size of data portion */
 dnss->srr.data = dnss->aptr;                   /* The record's data follows */
 
 GETSHORT(dnss->srr.size, dnss->aptr);          /* Size of data portion */
 dnss->srr.data = dnss->aptr;                   /* The record's data follows */
 

-/* Unchecked increment ok here since no further access on this iteration;
-will be checked on next at "R-name". */
-
-dnss->aptr += dnss->srr.size;                  /* Advance to next RR */
+/* skip over it, checking for a bogus size */
+if (dnss_inc_aptr(dnsa, dnss, dnss->srr.size))
+  goto null_return;

 
 /* Return a pointer to the dns_record structure within the dns_answer. This is
 for convenience so that the scans can use nice-looking for loops. */
 
 /* Return a pointer to the dns_record structure within the dns_answer. This is
 for convenience so that the scans can use nice-looking for loops. */

diff --git a/src/src/lookups/dnsdb.c b/src/src/lookups/dnsdb.c
index 355be1b5d4414bd7224e3d9963bdcde901df89d7..020dc9a526ad87c68049402dbc9ad70e45ae2a36 100644 (file)
--- a/src/src/lookups/dnsdb.c
+++ b/src/src/lookups/dnsdb.c
@@ -398,43 +398,60 @@ while ((domain = string_nextinlist(&keystring, &sep, NULL, 0)))
 
       if (type == T_TXT || type == T_SPF)
         {
 
       if (type == T_TXT || type == T_SPF)
         {

-        if (outsep2 == NULL)   /* output only the first item of data */
-          yield = string_catn(yield, US (rr->data+1), (rr->data)[0]);
+        if (!outsep2)                  /* output only the first item of data */
+         {
+         uschar n = (rr->data)[0];
+         /* size byte + data bytes must not excced the RRs length */
+         if (n + 1 <= rr->size)
+           yield = string_catn(yield, US (rr->data+1), n);
+         }

         else
           {
           /* output all items */
           int data_offset = 0;
           while (data_offset < rr->size)
             {
         else
           {
           /* output all items */
           int data_offset = 0;
           while (data_offset < rr->size)
             {

-            uschar chunk_len = (rr->data)[data_offset++];
-            if (outsep2[0] != '\0' && data_offset != 1)
+            uschar chunk_len = (rr->data)[data_offset];
+           int remain = rr->size - data_offset;
+
+           /* Apparently there are resolvers that do not check RRs before passing
+           them on, and glibc fails to do so.  So every application must...
+           Check for chunk len exceeding RR */
+
+           if (chunk_len > remain)
+             chunk_len = remain;
+
+            if (*outsep2  && data_offset != 0)

               yield = string_catn(yield, outsep2, 1);
               yield = string_catn(yield, outsep2, 1);

-            yield = string_catn(yield, US ((rr->data)+data_offset), chunk_len);
+            yield = string_catn(yield, US ((rr->data) + ++data_offset), --chunk_len);

             data_offset += chunk_len;
             }
           }
         }
       else if (type == T_TLSA)
             data_offset += chunk_len;
             }
           }
         }
       else if (type == T_TLSA)

-        {
-        uint8_t usage, selector, matching_type;
-        uint16_t payload_length;
-        uschar s[MAX_TLSA_EXPANDED_SIZE];
-       uschar * sp = s;
-        uschar * p = US rr->data;
+       if (rr->size < 3)
+         continue;
+       else
+         {
+         uint8_t usage, selector, matching_type;
+         uint16_t payload_length;
+         uschar s[MAX_TLSA_EXPANDED_SIZE];
+         uschar * sp = s;
+         uschar * p = US rr->data;
+
+         usage = *p++;
+         selector = *p++;
+         matching_type = *p++;
+         /* What's left after removing the first 3 bytes above */
+         payload_length = rr->size - 3;
+         sp += sprintf(CS s, "%d%c%d%c%d%c", usage, *outsep2,
+                 selector, *outsep2, matching_type, *outsep2);
+         /* Now append the cert/identifier, one hex char at a time */
+         while (payload_length-- > 0 && sp-s < (MAX_TLSA_EXPANDED_SIZE - 4))
+           sp += sprintf(CS sp, "%02x", *p++);

 
 

-        usage = *p++;
-        selector = *p++;
-        matching_type = *p++;
-        /* What's left after removing the first 3 bytes above */
-        payload_length = rr->size - 3;
-        sp += sprintf(CS s, "%d%c%d%c%d%c", usage, *outsep2,
-               selector, *outsep2, matching_type, *outsep2);
-        /* Now append the cert/identifier, one hex char at a time */
-       while (payload_length-- > 0 && sp-s < (MAX_TLSA_EXPANDED_SIZE - 4))
-          sp += sprintf(CS sp, "%02x", *p++);
-
-        yield = string_cat(yield, s);
-        }
+         yield = string_cat(yield, s);
+         }

       else   /* T_CNAME, T_CSA, T_MX, T_MXH, T_NS, T_PTR, T_SOA, T_SRV */
         {
         int priority, weight, port;
       else   /* T_CNAME, T_CSA, T_MX, T_MXH, T_NS, T_PTR, T_SOA, T_SRV */
         {
         int priority, weight, port;


@@ -444,17 +461,20 @@ while ((domain = string_nextinlist(&keystring, &sep, NULL, 0)))
        switch (type)
          {
          case T_MXH:
        switch (type)
          {
          case T_MXH:

+           if (rr->size < sizeof(u_int16_t)) continue;

            /* mxh ignores the priority number and includes only the hostnames */
            GETSHORT(priority, p);
            break;
 
          case T_MX:
            /* mxh ignores the priority number and includes only the hostnames */
            GETSHORT(priority, p);
            break;
 
          case T_MX:

+           if (rr->size < sizeof(u_int16_t)) continue;

            GETSHORT(priority, p);
            sprintf(CS s, "%d%c", priority, *outsep2);
            yield = string_cat(yield, s);
            break;
 
          case T_SRV:
            GETSHORT(priority, p);
            sprintf(CS s, "%d%c", priority, *outsep2);
            yield = string_cat(yield, s);
            break;
 
          case T_SRV:

+           if (rr->size < 3*sizeof(u_int16_t)) continue;

            GETSHORT(priority, p);
            GETSHORT(weight, p);
            GETSHORT(port, p);
            GETSHORT(priority, p);
            GETSHORT(weight, p);
            GETSHORT(port, p);


@@ -464,6 +484,7 @@ while ((domain = string_nextinlist(&keystring, &sep, NULL, 0)))
            break;
 
          case T_CSA:
            break;
 
          case T_CSA:

+           if (rr->size < 3*sizeof(u_int16_t)) continue;

            /* See acl_verify_csa() for more comments about CSA. */
            GETSHORT(priority, p);
            GETSHORT(weight, p);
            /* See acl_verify_csa() for more comments about CSA. */
            GETSHORT(priority, p);
            GETSHORT(weight, p);


@@ -514,7 +535,7 @@ while ((domain = string_nextinlist(&keystring, &sep, NULL, 0)))
 
        if (type == T_SOA && outsep2 != NULL)
          {
 
        if (type == T_SOA && outsep2 != NULL)
          {

-         unsigned long serial, refresh, retry, expire, minimum;
+         unsigned long serial = 0, refresh = 0, retry = 0, expire = 0, minimum = 0;

 
          p += rc;
          yield = string_catn(yield, outsep2, 1);
 
          p += rc;
          yield = string_catn(yield, outsep2, 1);


@@ -530,8 +551,11 @@ while ((domain = string_nextinlist(&keystring, &sep, NULL, 0)))
          else yield = string_cat(yield, s);
 
          p += rc;
          else yield = string_cat(yield, s);
 
          p += rc;

-         GETLONG(serial, p); GETLONG(refresh, p);
-         GETLONG(retry,  p); GETLONG(expire,  p); GETLONG(minimum, p);
+         if (rr->size >= p - rr->data - 5*sizeof(u_int32_t))
+           {
+           GETLONG(serial, p); GETLONG(refresh, p);
+           GETLONG(retry,  p); GETLONG(expire,  p); GETLONG(minimum, p);
+           }

          sprintf(CS s, "%c%lu%c%lu%c%lu%c%lu%c%lu",
            *outsep2, serial, *outsep2, refresh,
            *outsep2, retry,  *outsep2, expire,  *outsep2, minimum);
          sprintf(CS s, "%c%lu%c%lu%c%lu%c%lu%c%lu",
            *outsep2, serial, *outsep2, refresh,
            *outsep2, retry,  *outsep2, expire,  *outsep2, minimum);