resolv: Introduce struct resolv_context [BZ #21668]

struct resolv_context objects provide a temporary resolver context
which does not change during a name lookup operation.  Only when the
outmost context is created, the stub resolver configuration is
verified to be current (at present, only against previous res_init
calls).  Subsequent attempts to obtain the context will reuse the
result of the initial verification operation.

struct resolv_context can also be extended in the future to store
data which needs to be deallocated during thread cancellation.

1 files changed, 14 insertions, 5 deletions

diff --git a/resolv/nss_dns/dns-canon.c b/resolv/nss_dns/dns-canon.c
index 4276eb6542..7a5c39dc20 100644
--- a/resolv/nss_dns/dns-canon.c
+++ b/resolv/nss_dns/dns-canon.c
@@ -23,7 +23,8 @@
 #include <stdint.h>
 #include <arpa/nameser.h>
 #include <nsswitch.h>
-
+#include <resolv/resolv_context.h>
+#include <resolv/resolv-internal.h>
 
 #if PACKETSZ > 65536
 # define MAXPACKET	PACKETSZ
@@ -58,11 +59,19 @@ _nss_dns_getcanonname_r (const char *name, char *buffer, size_t buflen,
   } ansp = { .ptr = buf };
   enum nss_status status = NSS_STATUS_UNAVAIL;
 
+  struct resolv_context *ctx = __resolv_context_get ();
+  if (ctx == NULL)
+    {
+      *errnop = errno;
+      *h_errnop = NETDB_INTERNAL;
+      return NSS_STATUS_UNAVAIL;
+    }
+
   for (int i = 0; i < nqtypes; ++i)
     {
-      int r = __libc_res_nquery (&_res, name, ns_c_in, qtypes[i],
-				 buf, sizeof (buf), &ansp.ptr, NULL, NULL,
-				 NULL, NULL);
+      int r = __res_context_query (ctx, name, ns_c_in, qtypes[i],
+				   buf, sizeof (buf), &ansp.ptr, NULL, NULL,
+				   NULL, NULL);
       if (r > 0)
 	{
 	  /* We need to decode the response.  Just one question record.
@@ -168,6 +177,6 @@ _nss_dns_getcanonname_r (const char *name, char *buffer, size_t buflen,
 
   if (ansp.ptr != buf)
     free (ansp.ptr);
-
+  __resolv_context_put (ctx);
   return status;
 }