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java: do not try to malloc 0 elements in get_all_event_callbacks

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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.
This commit is contained in:
Pino Toscano
2017-03-03 13:50:46 +01:00
parent 4fc85f27c4
commit c6543875ae
1 changed files with 12 additions and 5 deletions
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17
java/handle.c
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@@ -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) {