_nss_nis_initgroups_dyn: Use struct scratch_buffer [BZ #18023]

diff --git a/nis/nss_nis/nis-initgroups.c b/nis/nss_nis/nis-initgroups.c
index a47b4d7ada..ca043d4e5a 100644
--- a/nis/nss_nis/nis-initgroups.c
+++ b/nis/nss_nis/nis-initgroups.c
@@ -16,7 +16,6 @@ 
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 
-#include <alloca.h>
 #include <ctype.h>
 #include <errno.h>
 #include <grp.h>
@@ -27,6 +26,7 @@ 
 #include <rpcsvc/yp.h>
 #include <rpcsvc/ypclnt.h>
 #include <sys/param.h>
+#include <scratch_buffer.h>
 
 #include "nss-nis.h"
 #include <libnsl.h>
@@ -120,27 +120,30 @@  internal_getgrent_r (struct group *grp, char *buffer, size_t buflen,
 static int
 get_uid (const char *user, uid_t *uidp)
 {
-  size_t buflen = sysconf (_SC_GETPW_R_SIZE_MAX);
-  char *buf = (char *) alloca (buflen);
+  struct scratch_buffer tmpbuf;
+  scratch_buffer_init (&tmpbuf);
 
   while (1)
     {
       struct passwd result;
       struct passwd *resp;
 
-      int r = getpwnam_r (user, &result, buf, buflen, &resp);
+      int r = getpwnam_r (user, &result, tmpbuf.data, tmpbuf.length, &resp);
       if (r == 0 && resp != NULL)
 	{
 	  *uidp = resp->pw_uid;
+	  scratch_buffer_free (&tmpbuf);
 	  return 0;
 	}
 
       if (r != ERANGE)
 	break;
 
-      buf = extend_alloca (buf, buflen, 2 * buflen);
+      if (!scratch_buffer_grow (&tmpbuf))
+	return 1;
     }
 
+  scratch_buffer_free (&tmpbuf);
   return 1;
 }
 
@@ -254,8 +257,6 @@  _nss_nis_initgroups_dyn (const char *user, gid_t group, long int *start,
     }
 
   struct group grpbuf, *g;
-  size_t buflen = sysconf (_SC_GETPW_R_SIZE_MAX);
-  char *tmpbuf;
   enum nss_status status;
   intern_t intern = { NULL, NULL, 0 };
   gid_t *groups = *groupsp;
@@ -264,15 +265,20 @@  _nss_nis_initgroups_dyn (const char *user, gid_t group, long int *start,
   if (status != NSS_STATUS_SUCCESS)
     return status;
 
-  tmpbuf = __alloca (buflen);
+  struct scratch_buffer tmpbuf;
+  scratch_buffer_init (&tmpbuf);
 
   while (1)
     {
       while ((status =
-	      internal_getgrent_r (&grpbuf, tmpbuf, buflen, errnop,
+	      internal_getgrent_r (&grpbuf, tmpbuf.data, tmpbuf.length, errnop,
 				   &intern)) == NSS_STATUS_TRYAGAIN
              && *errnop == ERANGE)
-	tmpbuf = extend_alloca (tmpbuf, buflen, 2 * buflen);
+	if (!scratch_buffer_grow (&tmpbuf))
+	  {
+	    status = NSS_STATUS_TRYAGAIN;
+	    goto done;
+	  }
 
       if (status != NSS_STATUS_SUCCESS)
 	{
@@ -331,6 +337,7 @@  done:
       intern.start = intern.start->next;
       free (intern.next);
     }
+  scratch_buffer_free (&tmpbuf);
 
   return status;
 }