Commit d90eeb8e authored by Alice Ryhl's avatar Alice Ryhl Committed by Greg Kroah-Hartman
Browse files

binder: remove "invalid inc weak" check 



There are no scenarios where a weak increment is invalid on binder_node.
The only possible case where it could be invalid is if the kernel
delivers BR_DECREFS to the process that owns the node, and then
increments the weak refcount again, effectively "reviving" a dead node.

However, that is not possible: when the BR_DECREFS command is delivered,
the kernel removes and frees the binder_node. The fact that you were
able to call binder_inc_node_nilocked() implies that the node is not yet
destroyed, which implies that BR_DECREFS has not been delivered to
userspace, so incrementing the weak refcount is valid.

Note that it's currently possible to trigger this condition if the owner
calls BINDER_THREAD_EXIT while node->has_weak_ref is true. This causes
BC_INCREFS on binder_ref instances to fail when they should not.

Cc: stable@vger.kernel.org
Fixes: 457b9a6f ("Staging: android: add binder driver")
Reported-by: default avatarYu-Ting Tseng <yutingtseng@google.com>
Signed-off-by: default avatarAlice Ryhl <aliceryhl@google.com>
Link: https://patch.msgid.link/20251015-binder-weak-inc-v1-1-7914b092c371@google.com


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 2463ae28

drivers/android/binder.c

+1 −10
Original line number Diff line number Diff line
@@ -851,18 +851,9 @@ static int binder_inc_node_nilocked(struct binder_node *node, int strong, 
	} else {

		if (!internal)

			node->local_weak_refs++;

		if (!node->has_weak_ref && list_empty(&node->work.entry)) {

			if (target_list == NULL) {

				pr_err("invalid inc weak node for %d\n",

					node->debug_id);

				return -EINVAL;

			}

			/*

			 * See comment above

			 */

		if (!node->has_weak_ref && target_list && list_empty(&node->work.entry))

			binder_enqueue_work_ilocked(&node->work, target_list);

	}

	}

	return 0;

}