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, 66 insertions, 38 deletions

diff --git a/resolv/nss_dns/dns-host.c b/resolv/nss_dns/dns-host.c
index 206924de86..9d7ceb1691 100644
--- a/resolv/nss_dns/dns-host.c
+++ b/resolv/nss_dns/dns-host.c
@@ -84,6 +84,7 @@
 
 /* Get implementeation for some internal functions.  */
 #include <resolv/resolv-internal.h>
+#include <resolv/resolv_context.h>
 #include <resolv/mapv4v6addr.h>
 #include <resolv/mapv4v6hostent.h>
 
@@ -121,13 +122,13 @@ static enum nss_status gaih_getanswer (const querybuf *answer1, int anslen1,
 				       int *errnop, int *h_errnop,
 				       int32_t *ttlp);
 
-extern enum nss_status _nss_dns_gethostbyname3_r (const char *name, int af,
-						  struct hostent *result,
-						  char *buffer, size_t buflen,
-						  int *errnop, int *h_errnop,
-						  int32_t *ttlp,
-						  char **canonp);
-hidden_proto (_nss_dns_gethostbyname3_r)
+static enum nss_status gethostbyname3_context (struct resolv_context *ctx,
+					       const char *name, int af,
+					       struct hostent *result,
+					       char *buffer, size_t buflen,
+					       int *errnop, int *h_errnop,
+					       int32_t *ttlp,
+					       char **canonp);
 
 /* Return the expected RDATA length for an address record type (A or
    AAAA).  */
@@ -145,11 +146,31 @@ rrtype_to_rdata_length (int type)
     }
 }
 
+
 enum nss_status
 _nss_dns_gethostbyname3_r (const char *name, int af, struct hostent *result,
 			   char *buffer, size_t buflen, int *errnop,
 			   int *h_errnop, int32_t *ttlp, char **canonp)
 {
+  struct resolv_context *ctx = __resolv_context_get ();
+  if (ctx == NULL)
+    {
+      *errnop = errno;
+      *h_errnop = NETDB_INTERNAL;
+      return NSS_STATUS_UNAVAIL;
+    }
+  enum nss_status status = gethostbyname3_context
+    (ctx, name, af, result, buffer, buflen, errnop, h_errnop, ttlp, canonp);
+  __resolv_context_put (ctx);
+  return status;
+}
+
+static enum nss_status
+gethostbyname3_context (struct resolv_context *ctx,
+			const char *name, int af, struct hostent *result,
+			char *buffer, size_t buflen, int *errnop,
+			int *h_errnop, int32_t *ttlp, char **canonp)
+{
   union
   {
     querybuf *buf;
@@ -163,13 +184,6 @@ _nss_dns_gethostbyname3_r (const char *name, int af, struct hostent *result,
   int olderr = errno;
   enum nss_status status;
 
-  if (__res_maybe_init (&_res, 0) == -1)
-    {
-      *errnop = errno;
-      *h_errnop = NETDB_INTERNAL;
-      return NSS_STATUS_UNAVAIL;
-    }
-
   switch (af) {
   case AF_INET:
     size = INADDRSZ;
@@ -194,13 +208,13 @@ _nss_dns_gethostbyname3_r (const char *name, int af, struct hostent *result,
    * function that looks up host names.
    */
   if (strchr (name, '.') == NULL
-      && (cp = res_hostalias (&_res, name, tmp, sizeof (tmp))) != NULL)
+      && (cp = __res_context_hostalias (ctx, name, tmp, sizeof (tmp))) != NULL)
     name = cp;
 
   host_buffer.buf = orig_host_buffer = (querybuf *) alloca (1024);
 
-  n = __libc_res_nsearch (&_res, name, C_IN, type, host_buffer.buf->buf,
-			  1024, &host_buffer.ptr, NULL, NULL, NULL, NULL);
+  n = __res_context_search (ctx, name, C_IN, type, host_buffer.buf->buf,
+			    1024, &host_buffer.ptr, NULL, NULL, NULL, NULL);
   if (n < 0)
     {
       switch (errno)
@@ -232,10 +246,10 @@ _nss_dns_gethostbyname3_r (const char *name, int af, struct hostent *result,
 	 by having the RES_USE_INET6 bit in _res.options set, we try
 	 another lookup.  */
       if (af == AF_INET6 && res_use_inet6 ())
-	n = __libc_res_nsearch (&_res, name, C_IN, T_A, host_buffer.buf->buf,
-				host_buffer.buf != orig_host_buffer
-				? MAXPACKET : 1024, &host_buffer.ptr,
-				NULL, NULL, NULL, NULL);
+	n = __res_context_search (ctx, name, C_IN, T_A, host_buffer.buf->buf,
+				  host_buffer.buf != orig_host_buffer
+				  ? MAXPACKET : 1024, &host_buffer.ptr,
+				  NULL, NULL, NULL, NULL);
 
       if (n < 0)
 	{
@@ -256,8 +270,6 @@ _nss_dns_gethostbyname3_r (const char *name, int af, struct hostent *result,
     free (host_buffer.buf);
   return status;
 }
-hidden_def (_nss_dns_gethostbyname3_r)
-
 
 enum nss_status
 _nss_dns_gethostbyname2_r (const char *name, int af, struct hostent *result,
@@ -274,15 +286,21 @@ _nss_dns_gethostbyname_r (const char *name, struct hostent *result,
 			  char *buffer, size_t buflen, int *errnop,
 			  int *h_errnop)
 {
+  struct resolv_context *ctx = __resolv_context_get ();
+  if (ctx == NULL)
+    {
+      *errnop = errno;
+      *h_errnop = NETDB_INTERNAL;
+      return NSS_STATUS_UNAVAIL;
+    }
   enum nss_status status = NSS_STATUS_NOTFOUND;
-
   if (res_use_inet6 ())
-    status = _nss_dns_gethostbyname3_r (name, AF_INET6, result, buffer,
-					buflen, errnop, h_errnop, NULL, NULL);
+    status = gethostbyname3_context (ctx, name, AF_INET6, result, buffer,
+				     buflen, errnop, h_errnop, NULL, NULL);
   if (status == NSS_STATUS_NOTFOUND)
-    status = _nss_dns_gethostbyname3_r (name, AF_INET, result, buffer,
-					buflen, errnop, h_errnop, NULL, NULL);
-
+    status = gethostbyname3_context (ctx, name, AF_INET, result, buffer,
+				     buflen, errnop, h_errnop, NULL, NULL);
+  __resolv_context_put (ctx);
   return status;
 }
 
@@ -292,7 +310,8 @@ _nss_dns_gethostbyname4_r (const char *name, struct gaih_addrtuple **pat,
 			   char *buffer, size_t buflen, int *errnop,
 			   int *herrnop, int32_t *ttlp)
 {
-  if (__res_maybe_init (&_res, 0) == -1)
+  struct resolv_context *ctx = __resolv_context_get ();
+  if (ctx == NULL)
     {
       *errnop = errno;
       *herrnop = NETDB_INTERNAL;
@@ -307,7 +326,7 @@ _nss_dns_gethostbyname4_r (const char *name, struct gaih_addrtuple **pat,
   if (strchr (name, '.') == NULL)
     {
       char *tmp = alloca (NS_MAXDNAME);
-      const char *cp = res_hostalias (&_res, name, tmp, NS_MAXDNAME);
+      const char *cp = __res_context_hostalias (ctx, name, tmp, NS_MAXDNAME);
       if (cp != NULL)
 	name = cp;
     }
@@ -326,9 +345,9 @@ _nss_dns_gethostbyname4_r (const char *name, struct gaih_addrtuple **pat,
 
   int olderr = errno;
   enum nss_status status;
-  int n = __libc_res_nsearch (&_res, name, C_IN, T_QUERY_A_AND_AAAA,
-			      host_buffer.buf->buf, 2048, &host_buffer.ptr,
-			      &ans2p, &nans2p, &resplen2, &ans2p_malloced);
+  int n = __res_context_search (ctx, name, C_IN, T_QUERY_A_AND_AAAA,
+				host_buffer.buf->buf, 2048, &host_buffer.ptr,
+				&ans2p, &nans2p, &resplen2, &ans2p_malloced);
   if (n >= 0)
     {
       status = gaih_getanswer (host_buffer.buf, n, (const querybuf *) ans2p,
@@ -371,6 +390,7 @@ _nss_dns_gethostbyname4_r (const char *name, struct gaih_addrtuple **pat,
   if (host_buffer.buf != orig_host_buffer)
     free (host_buffer.buf);
 
+  __resolv_context_put (ctx);
   return status;
 }
 
@@ -423,7 +443,8 @@ _nss_dns_gethostbyaddr2_r (const void *addr, socklen_t len, int af,
 
  host_data = (struct host_data *) buffer;
 
-  if (__res_maybe_init (&_res, 0) == -1)
+  struct resolv_context *ctx = __resolv_context_get ();
+  if (ctx == NULL)
     {
       *errnop = errno;
       *h_errnop = NETDB_INTERNAL;
@@ -453,12 +474,14 @@ _nss_dns_gethostbyaddr2_r (const void *addr, socklen_t len, int af,
     default:
       *errnop = EAFNOSUPPORT;
       *h_errnop = NETDB_INTERNAL;
+      __resolv_context_put (ctx);
       return NSS_STATUS_UNAVAIL;
     }
   if (size > len)
     {
       *errnop = EAFNOSUPPORT;
       *h_errnop = NETDB_INTERNAL;
+      __resolv_context_put (ctx);
       return NSS_STATUS_UNAVAIL;
     }
 
@@ -487,14 +510,15 @@ _nss_dns_gethostbyaddr2_r (const void *addr, socklen_t len, int af,
       break;
     }
 
-  n = __libc_res_nquery (&_res, qbuf, C_IN, T_PTR, host_buffer.buf->buf,
-			 1024, &host_buffer.ptr, NULL, NULL, NULL, NULL);
+  n = __res_context_query (ctx, qbuf, C_IN, T_PTR, host_buffer.buf->buf,
+			   1024, &host_buffer.ptr, NULL, NULL, NULL, NULL);
   if (n < 0)
     {
       *h_errnop = h_errno;
       __set_errno (olderr);
       if (host_buffer.buf != orig_host_buffer)
 	free (host_buffer.buf);
+      __resolv_context_put (ctx);
       return errno == ECONNREFUSED ? NSS_STATUS_UNAVAIL : NSS_STATUS_NOTFOUND;
     }
 
@@ -503,7 +527,10 @@ _nss_dns_gethostbyaddr2_r (const void *addr, socklen_t len, int af,
   if (host_buffer.buf != orig_host_buffer)
     free (host_buffer.buf);
   if (status != NSS_STATUS_SUCCESS)
-    return status;
+    {
+      __resolv_context_put (ctx);
+      return status;
+    }
 
   result->h_addrtype = af;
   result->h_length = len;
@@ -511,6 +538,7 @@ _nss_dns_gethostbyaddr2_r (const void *addr, socklen_t len, int af,
   host_data->h_addr_ptrs[0] = (char *) host_data->host_addr;
   host_data->h_addr_ptrs[1] = NULL;
   *h_errnop = NETDB_SUCCESS;
+  __resolv_context_put (ctx);
   return NSS_STATUS_SUCCESS;
 }
 hidden_def (_nss_dns_gethostbyaddr2_r)