Cygwin: resolver: more fixes

Cygwin: resolver: more fixes

[Anton Lavrentiev]

Proposed are two fixes for more little bugs in the resolver.  The first
one fixes the ID field returned in the response to match the ID of the
request (even in the case when the OS-supplied native resolver is used).
The second one is about the standard compliance (when the response is
relayed from the native OS resolver):  the targets in SRV records
should never be compressed.

[PATCH 1/2] Cygwin: resolver: Fix to match response ID with request ID

[Anton Lavrentiev]

In case when the native OS resolver is used (via os_query) the returned
response ID is always 0.  It should actually match the ID passed in to
res_send() in the DNS request header.  This patch fixes that
---
 winsup/cygwin/libc/minires-os-if.c | 6 +++++-
 winsup/cygwin/libc/minires.c       | 7 ++++++-
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/winsup/cygwin/libc/minires-os-if.c b/winsup/cygwin/libc/minires-os-if.c
index c4183db9c..8d3178f70 100644
--- a/winsup/cygwin/libc/minires-os-if.c
+++ b/winsup/cygwin/libc/minires-os-if.c
@@ -189,10 +189,14 @@ static int cygwin_query(res_state statp, const char * DomName, int Class, int Ty
   DWORD section;
   int len, counts[4] = {0, 0, 0, 0}, debug = statp->options & RES_DEBUG;
   unsigned char * dnptrs[256], * ptr;
+  unsigned short Id = 0;
 
   dnptrs[0] = AnsPtr;
   dnptrs[1] = NULL;
 
+  if (AnsLength >= 2)
+    memcpy(&Id, AnsPtr, 2);
+
   memset(AnsPtr, 0, AnsLength);
 
   if (Class != ns_c_in) {
@@ -294,7 +298,7 @@ static int cygwin_query(res_state statp, const char * DomName, int Class, int Ty
 done:
   if (HFIXEDSZ <= AnsLength) {
     ptr = AnsPtr;
-    PUTSHORT(0, ptr); /* Id */
+    PUTSHORT(Id, ptr);
     PUTSHORT((QR << 8) + RA + RD, ptr);
     for (section = 0; section < DIM(counts); section++) {
       PUTSHORT(counts[section], ptr);
diff --git a/winsup/cygwin/libc/minires.c b/winsup/cygwin/libc/minires.c
index fdc6087f5..b540f6a1b 100644
--- a/winsup/cygwin/libc/minires.c
+++ b/winsup/cygwin/libc/minires.c
@@ -450,6 +450,8 @@ int res_nsend( res_state statp, const unsigned char * MsgPtr,
       ptr += len;
       GETSHORT(Type, ptr);
       GETSHORT(Class, ptr);
+      if (AnsLength >= 2)
+          memcpy(AnsPtr, MsgPtr, 2);
       return ((os_query_t *) statp->os_query)(statp, DomName, Class, Type, AnsPtr, AnsLength);
     }
     else {
@@ -709,8 +711,11 @@ int res_nquery( res_state statp, const char * DomName, int Class, int Type,
   statp->res_h_errno = NETDB_SUCCESS;
 
   /* If a hook exists to a native implementation, use it */
-  if (statp->os_query)
+  if (statp->os_query) {
+    if (AnsLength >= 2)
+        memset(AnsPtr, 0/*Id*/, 2);
     return ((os_query_t *) statp->os_query)(statp, DomName, Class, Type, AnsPtr, AnsLength);
+  }
 
   if ((len = res_nmkquery (statp, QUERY, DomName, Class, Type,
 			   0, 0, 0, packet, PACKETSZ)) < 0)
-- 
2.33.0

[PATCH 2/2] Cygwin: resolver: Targets in SRV DNS responses may not be compressed

[Anton Lavrentiev]

RFC2782 clearly says so yet it's a common misconception to perform the
compression in the violation of the standard.  This patch fixes that
---
 winsup/cygwin/libc/minires-os-if.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/winsup/cygwin/libc/minires-os-if.c b/winsup/cygwin/libc/minires-os-if.c
index 8d3178f70..5da1c0c55 100644
--- a/winsup/cygwin/libc/minires-os-if.c
+++ b/winsup/cygwin/libc/minires-os-if.c
@@ -159,6 +159,7 @@ static unsigned char * write_record(unsigned char * ptr, PDNS_RECORD rr,
       PUTSHORT(rr->Data.SRV.wWeight, ptr);
       PUTSHORT(rr->Data.SRV.wPort, ptr);
     }
+    dnptrs = 0;  /* compression not allowed */
     PUTDOMAIN(rr->Data.SRV.pNameTarget, ptr);
     break;
   default:
-- 
2.33.0