[PATCH] nss_files: Use struct scratch_buffer for gethostbyname [BZ #18023]

[fweimer at redhat dot com (Florian Weimer)]

2017-09-04  Florian Weimer  <fweimer@redhat.com>

	[BZ #18023]
	* nss/nss_files/files-hosts.c (gethostbyname3_multi): Use struct
	scratch_buffer.

diff --git a/nss/nss_files/files-hosts.c b/nss/nss_files/files-hosts.c
index 867c10c2ef..c2cd07584c 100644
--- a/nss/nss_files/files-hosts.c
+++ b/nss/nss_files/files-hosts.c
@@ -22,6 +22,7 @@
 #include <arpa/nameser.h>
 #include <netdb.h>
 #include <resolv/resolv-internal.h>
+#include <scratch_buffer.h>
 
 
 /* Get implementation for some internal functions.  */
@@ -121,15 +122,12 @@ gethostbyname3_multi (FILE * stream, const char *name, int af,
 		      int *errnop, int *herrnop, int flags)
 {
   /* We have to get all host entries from the file.  */
-  size_t tmp_buflen = MIN (buflen, 4096);
-  char tmp_buffer_stack[tmp_buflen]
-    __attribute__ ((__aligned__ (__alignof__ (struct hostent_data))));
-  char *tmp_buffer = tmp_buffer_stack;
+  struct scratch_buffer tmp_buffer;
+  scratch_buffer_init (&tmp_buffer);
   struct hostent tmp_result_buf;
   int naddrs = 1;
   int naliases = 0;
   char *bufferend;
-  bool tmp_buffer_malloced = false;
   enum nss_status status;
 
   while (result->h_aliases[naliases] != NULL)
@@ -138,8 +136,8 @@ gethostbyname3_multi (FILE * stream, const char *name, int af,
   bufferend = (char *) &result->h_aliases[naliases + 1];
 
  again:
-  while ((status = internal_getent (stream, &tmp_result_buf, tmp_buffer,
-				    tmp_buflen, errnop, herrnop, af,
+  while ((status = internal_getent (stream, &tmp_result_buf, tmp_buffer.data,
+				    tmp_buffer.length, errnop, herrnop, af,
 				    flags))
 	 == NSS_STATUS_SUCCESS)
     {
@@ -266,52 +264,18 @@ gethostbyname3_multi (FILE * stream, const char *name, int af,
 
   if (status == NSS_STATUS_TRYAGAIN)
     {
-      size_t newsize = 2 * tmp_buflen;
-      if (tmp_buffer_malloced)
+      if (!scratch_buffer_grow (&tmp_buffer))
 	{
-	  char *newp = realloc (tmp_buffer, newsize);
-	  if (newp != NULL)
-	    {
-	      assert ((((uintptr_t) newp)
-		       & (__alignof__ (struct hostent_data) - 1))
-		      == 0);
-	      tmp_buffer = newp;
-	      tmp_buflen = newsize;
-	      goto again;
-	    }
-	}
-      else if (!__libc_use_alloca (buflen + newsize))
-	{
-	  tmp_buffer = malloc (newsize);
-	  if (tmp_buffer != NULL)
-	    {
-	      assert ((((uintptr_t) tmp_buffer)
-		       & (__alignof__ (struct hostent_data) - 1))
-		      == 0);
-	      tmp_buffer_malloced = true;
-	      tmp_buflen = newsize;
-	      goto again;
-	    }
+	  *herrnop = NETDB_INTERNAL;
+	  status = NSS_STATUS_TRYAGAIN;
 	}
       else
-	{
-	  tmp_buffer
-	    = extend_alloca (tmp_buffer, tmp_buflen,
-			     newsize
-			     + __alignof__ (struct hostent_data));
-	  tmp_buffer = (char *) (((uintptr_t) tmp_buffer
-				  + __alignof__ (struct hostent_data)
-				  - 1)
-				 & ~(__alignof__ (struct hostent_data)
-				     - 1));
-	  goto again;
-	}
+	goto again;
     }
   else
     status = NSS_STATUS_SUCCESS;
  out:
-  if (tmp_buffer_malloced)
-    free (tmp_buffer);
+  scratch_buffer_free (&tmp_buffer);
   return status;
 }