[Libguestfs] [PATCH v2 4/4] java: 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. --- java/handle.c | 17 ++++++++++++----- 1 file changed, 12 insertions(+), 5 deletions(-) diff --git a/java/handle.c b/java/handle.c index f225361..0993f33 100644 --- a/java/handle.c +++ b/java/handle.c @@ -85,7 +85,7 @@ Java_com_redhat_et_libguestfs_GuestFS__1close (JNIEnv *env, jobject obj, jlong jg) { guestfs_h *g = (guestfs_h *) (long) jg; - size_t len, i; + size_t len; struct callback_data **data; /* There is a nasty, difficult to solve case here where the @@ -96,11 +96,14 @@ Java_com_redhat_et_libguestfs_GuestFS__1close guestfs_close (g); - for (i = 0; i < len; ++i) { - (*env)->DeleteGlobalRef (env, data[i]->callback); - free (data[i]); + if (len > 0) { + size_t i; + for (i = 0; i < len; ++i) { + (*env)->DeleteGlobalRef (env, data[i]->callback); + free (data[i]); + } + free (data); } - free (data); } /* See EventCallback interface. */ @@ -274,6 +277,10 @@ get_all_event_callbacks (JNIEnv *env, guestfs_h *g, size_t *len_rtn) data = 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 (struct callback_data *) * (*len_rtn)); if (r == NULL) { -- 2.9.3