Re: [PATCH v3] char: tty3270: fix a missing check on list iterator

Jiri Slaby
2022-03-29T06:07:24Z

On 28. 03. 22, 12:27, Xiaomeng Tong wrote:
> On Mon, 28 Mar 2022 12:09:59 +0200, Jiri Slaby wrote:
>> On 28. 03. 22, 11:35, Xiaomeng Tong wrote:
>>> The bug is here:
>>> if (s->len != flen) {
>>>
>>> The list iterator 's' will point to a bogus position containing
>>> HEAD if the list is empty or no element is found.
>>
>> Could you also explain how that can happen?
>>
>
> When list_for_each_entry_* do not early exits (if the list is empty
> or no break/goto/return hit inside the loop), it will set pos ('s' here)
> with a bogus pointer that point to a invalid struct computed based
> on &HEAD using container_of.
>
> #define list_for_each_entry(pos, head, member) \
> for (pos = list_first_entry(head, typeof(*pos), member); \
> !list_entry_is_head(pos, head, member); \
> pos = list_next_entry(pos, member))

No, I didn't mean what happens on that site on the code level. I think
everyone understands that. Instead, I meant: what circumstances lead to
this _situation_ in reality?

thanks,
--
js
suse labs