[Libguestfs] [PATCH v2 3/4] ruby: do not try to malloc 0 elements in get_all_event_callbacks

In case there are no event handlers registered with the handle, get_all_event_callbacks will count 0 elements, trying to malloc a buffer of that size. POSIX says that this can result in either a null pointer, or an unusable pointer. Short-circuit get_all_event_callbacks to allocate nothing when there are no events, making sure to use its results only when there were events. --- ruby/ext/guestfs/handle.c | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-) diff --git a/ruby/ext/guestfs/handle.c b/ruby/ext/guestfs/handle.c index aa10825..b04192d 100644 --- a/ruby/ext/guestfs/handle.c +++ b/ruby/ext/guestfs/handle.c @@ -54,7 +54,7 @@ free_handle (void *gvp) * the callbacks that we are about to invoke, resulting in * a double-free. XXX */ - size_t len, i; + size_t len; VALUE **roots = get_all_event_callbacks (g, &len); /* Close the handle: this could invoke callbacks from the list @@ -64,11 +64,14 @@ free_handle (void *gvp) guestfs_close (g); /* Now unregister the global roots. */ - for (i = 0; i < len; ++i) { - rb_gc_unregister_address (roots[i]); - free (roots[i]); + if (len > 0) { + size_t i; + for (i = 0; i < len; ++i) { + rb_gc_unregister_address (roots[i]); + free (roots[i]); + } + free (roots); } - free (roots); } } @@ -384,6 +387,10 @@ get_all_event_callbacks (guestfs_h *g, size_t *len_rtn) root = guestfs_next_private (g, &key); } + /* No events, so no need to allocate anything. */ + if (*len_rtn == 0) + return NULL; + /* Copy them into the return array. */ r = malloc (sizeof (VALUE *) * (*len_rtn)); if (r == NULL) -- 2.9.3