--- src/xheader.c.orig	2004-09-06 06:31:14.000000000 -0500
+++ src/xheader.c	2006-02-08 16:59:46.000000000 -0500
@@ -783,6 +783,32 @@ code_num (uintmax_t value, char const *k
   xheader_print (xhdr, keyword, sbuf);
 }
 
+static bool
+decode_num (uintmax_t *num, char const *arg, uintmax_t maxval,
+        char const *keyword)
+{
+  uintmax_t u;
+  char *arg_lim;
+
+  if (! (ISDIGIT (*arg)
+     && (errno = 0, u = strtoumax (arg, &arg_lim, 10), !*arg_lim)))
+    {
+      ERROR ((0, 0, _("Malformed extended header: invalid %s=%s"),
+          keyword, arg));
+      return false;
+    }
+
+  if (! (u <= maxval && errno != ERANGE))
+    {
+      ERROR ((0, 0, _("Extended header %s=%s is out of range"),
+        keyword, arg));
+      return false;
+    }
+
+  *num = u;
+  return true;
+}
+
 static void
 dummy_coder (struct tar_stat_info const *st __attribute__ ((unused)),
 	     char const *keyword __attribute__ ((unused)),
@@ -821,7 +847,7 @@ static void
 gid_decoder (struct tar_stat_info *st, char const *arg)
 {
   uintmax_t u;
-  if (xstrtoumax (arg, NULL, 10, &u, "") == LONGINT_OK)
+  if (decode_num (&u, arg, TYPE_MAXIMUM (gid_t), "gid"))
     st->stat.st_gid = u;
 }
 
@@ -903,7 +929,7 @@ static void
 size_decoder (struct tar_stat_info *st, char const *arg)
 {
   uintmax_t u;
-  if (xstrtoumax (arg, NULL, 10, &u, "") == LONGINT_OK)
+  if (decode_num (&u, arg, TYPE_MAXIMUM (off_t), "size"))
     st->archive_file_size = st->stat.st_size = u;
 }
 
@@ -918,7 +944,7 @@ static void
 uid_decoder (struct tar_stat_info *st, char const *arg)
 {
   uintmax_t u;
-  if (xstrtoumax (arg, NULL, 10, &u, "") == LONGINT_OK)
+  if (decode_num (&u, arg, TYPE_MAXIMUM (uid_t), "uid"))
     st->stat.st_uid = u;
 }
 
@@ -946,7 +972,7 @@ static void
 sparse_size_decoder (struct tar_stat_info *st, char const *arg)
 {
   uintmax_t u;
-  if (xstrtoumax (arg, NULL, 10, &u, "") == LONGINT_OK)
+  if (decode_num (&u, arg, TYPE_MAXIMUM (off_t), "GNU.sparse.size"))
     st->stat.st_size = u;
 }
 
@@ -962,10 +988,10 @@ static void
 sparse_numblocks_decoder (struct tar_stat_info *st, char const *arg)
 {
   uintmax_t u;
-  if (xstrtoumax (arg, NULL, 10, &u, "") == LONGINT_OK)
+  if (decode_num (&u, arg, SIZE_MAX, "GNU.sparse.numblocks"))
     {
       st->sparse_map_size = u;
-      st->sparse_map = calloc(st->sparse_map_size, sizeof(st->sparse_map[0]));
+      st->sparse_map = xcalloc (u, sizeof st->sparse_map[0]);
       st->sparse_map_avail = 0;
     }
 }
@@ -982,8 +1008,14 @@ static void
 sparse_offset_decoder (struct tar_stat_info *st, char const *arg)
 {
   uintmax_t u;
-  if (xstrtoumax (arg, NULL, 10, &u, "") == LONGINT_OK)
+  if (decode_num (&u, arg, TYPE_MAXIMUM (off_t), "GNU.sparse.offset"))
+    {
+      if (st->sparse_map_avail < st->sparse_map_size)
     st->sparse_map[st->sparse_map_avail].offset = u;
+      else
+    ERROR ((0, 0, _("Malformed extended header: excess %s=%s"),
+        "GNU.sparse.offset", arg));
+    }
 }
 
 static void
@@ -998,15 +1030,13 @@ static void
 sparse_numbytes_decoder (struct tar_stat_info *st, char const *arg)
 {
   uintmax_t u;
-  if (xstrtoumax (arg, NULL, 10, &u, "") == LONGINT_OK)
+  if (decode_num (&u, arg, SIZE_MAX, "GNU.sparse.numbytes"))
     {
       if (st->sparse_map_avail == st->sparse_map_size)
-	{
-	  st->sparse_map_size *= 2;
-	  st->sparse_map = xrealloc (st->sparse_map,
-				     st->sparse_map_size
-				     * sizeof st->sparse_map[0]);
-	}
+        st->sparse_map = x2nrealloc (st->sparse_map,
+                                    &st->sparse_map_size,
+                                    sizeof st->sparse_map[0]);
+
       st->sparse_map[st->sparse_map_avail++].numbytes = u;
     }
 }