[svn-r12831] Changed the API for "unpacking" an external link value to take the size of

the linkval buffer, per Elena and Frank's suggestions while revising
the documentation.  Added error checking using this size, as well as a
couple of tests.

Tested on juniper, kagiso, and sol.

1 files changed, 26 insertions, 5 deletions

diff --git a/src/H5Lexternal.c b/src/H5Lexternal.c
index 4ca5c83..ab2d7e6 100644
--- a/src/H5Lexternal.c
+++ b/src/H5Lexternal.c
@@ -292,7 +292,7 @@ done:
 
 
 /*-------------------------------------------------------------------------
- * Function: H5Lunpack_elink_path
+ * Function: H5Lunpack_elink_val
  *
  * Purpose: Given a buffer holding the "link value" from an external link,
  *              gets pointers to the filename and object path within the
@@ -315,7 +315,8 @@ done:
  *-------------------------------------------------------------------------
  */
 herr_t
-H5Lunpack_elink_val(char *ext_linkval, char **filename, char **obj_path)
+H5Lunpack_elink_val(char *ext_linkval, size_t link_size, char **filename,
+                    char **obj_path)
 {
     size_t      len;                /* Length of the filename in the linkval*/
     herr_t      ret_value=SUCCEED;  /* Return value */
@@ -325,15 +326,35 @@ H5Lunpack_elink_val(char *ext_linkval, char **filename, char **obj_path)
 
     if(ext_linkval == NULL )
         HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "not an external link linkval buffer")
+    if(link_size <= 1)
+        HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "not a valid external link buffer")
 
+    /* Try to do some error checking.  If the last character in the linkval
+     * (the last character of obj_path) isn't NULL, then something's wrong.
+     */
+    if(ext_linkval[link_size-1] != '\0')
+        HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "linkval buffer is not NULL-terminated")
+
+    /* We're now guaranteed that HDstrlen won't segfault, since the buffer has
+     * at least one NULL in it.
+     */
+    len = HDstrlen(ext_linkval);
+
+    /* If the first NULL we found was at the very end of the buffer, then
+     * this external link value has no object name and is invalid.
+     */
+    if(len + 1>= link_size)
+        HGOTO_ERROR(H5E_ARGS, H5E_BADVALUE, FAIL, "linkval buffer doesn't contain an object path")
+
+    /* If we got here then the buffer contains (at least) two strings packed
+     * in the correct way.  Assume it's correct and return pointers to the
+     * filename and object path.
+     */
     if(filename != NULL)
         *filename = ext_linkval;
 
     if(obj_path != NULL)
-    {
-        len = HDstrlen(ext_linkval);
         *obj_path = ext_linkval + len + 1;  /* Add one for NULL terminator */
-    }
 
 done:
     FUNC_LEAVE_API(ret_value)